Tunneling and Percolation Behavior in Granular Metals

The nature of the percolation process in granular metals is examined for the first time by a computer simulation of a system of metallic grains embedded in an insulating matrix. Assuming that the intergrain conduction is due to quantum mechanical tunneling it is found that a percolation-like critical behavior of the conductivity is obtained, but that a percolation universal behavior will be found only in a very special case. In contrast, the behavior of the electrical noise does not deviate substantially from the universal one. Comparison of these results with recent experimental observations suggests that in the metallic range, both transport properties are controlled by the continuous metallic network rather than by intergrain tunnelin.. We propose that the metallic network resembles the previously studied system of ‘inverted random voids’.

Effect of deviation from the mid-sagittal plane on the measurement of fetal nuchal translucency

OBJECTIVE

Screening for trisomy 21 by fetal nuchal translucency (NT) thickness at 11 to 13 + 6 weeks' gestation requires an appropriate examination of the NT. Errors in the assessment of NT may lead to an under- or overestimation of the NT and to incorrect patient-specific risks. In this study we aimed to examine the importance of the mid-sagittal section and whether the acquired plane of the head and face influences the measurement of the fetal NT thickness.

METHODS

Sixty three-dimensional volumes of the fetal head and face in a mid-sagittal plane were acquired. NT thickness was firstly measured in the mid-sagittal plane according to the guidelines of The Fetal Medicine Foundation. The head was then rotated by steps of 5 degrees up to 25 degrees around the mid-point of the biparietal diameter and occipitofrontal diameter and NT was measured again. All six NT measurements were taken by the same operator, Operator A, who on completion of the assessment of the 60 volumes repeated all the measurements. The whole process was then repeated by Operator B. Both operators were blinded to each others' measurements.

RESULTS

In the true mid-sagittal plane, the mean NT was 1.9 mm and it was above the expected median in 72.5% of the measurements. At a deviation of 15 degrees , mean NT was 1.5 mm, and 36.3% of the measurements were above the expected median. At a deviation of 25 degrees , mean NT was reduced to 1.3 mm and 17.9% of the measurements were above the expected median.

CONCLUSION

Fetal NT thickness is greatest in the mid-sagittal plane. Increasing deviation away from the mid-sagittal plane results in progressive underestimation of the fetal NT thickness and so to a corresponding underestimation of the patient-specific risk.

Prenatal diagnosis and management of a fetal intra-abdominal teratoma: a case report and review of the literature

We report on a case of a large intra-abdominal teratoma diagnosed antenatally and managed successfully after birth. Intra-abdominal teratomas are rare in prenatal life. Ultrasound examination shows a heterogenic tumor with cystic and solid components. After postpartum surgical removal, the prognosis is generally good.