The science of ART

The methods of gamete manipulation used in assisted reproductive technology (ART) are rapidly proliferating and in some instances outpacing the underlying science. In this review, we discuss two major advances in the ART laboratory-intracytoplasmic sperm injection and extended embryo culture before embryo transfer. We outline the rationale for these approaches, discuss results of experiments obtained from animal model systems and human preimplantation embryos that provide the scientific basis for these procedures, and point out potential concerns that have arisen from these studies.     

Spontaneous ordering of oxide nanostructures

We report the spontaneous formation of uniformly distributed arrays of "tips" (tall conical hillocks) upon oxidation of palladium (Pd) thin films. The formation of the palladium oxide tips depended on the thickness and granularity of the Pd film and on annealing and oxidation conditions. As the Pd film thickness increased from 40 to 200 nanometers, the average height of the tips increased from 0.5 to 1.2 micrometers, their height distribution became broader, and their density decreased from 55 x 10(6) to 12 x 10(6) per square centimeter. Enhanced photoelectron emission from locations corresponding to the tips suggests their possible use in field emission applications.     

Convergent and alternative designs in the digital adhesive pads of scincid lizards

Prasinohaema virens, an arboreal scincid lizard, differs from its closest relatives in that it exhibits subdigital adhesive setae resembling those of anoles in shape and those of geckos in some aspects of size. The other scincid species in this genus as well as those in a presumed ancestral genus exhibit pad scales with surface folds and ruffles but no setae; at least one of these species uses an adhesive grip similar to that of anoles and geckos. Thus, there appear to be two strikingly different epidermal specializations for adhesive grip within this small radiation.     

A positive test of East Antarctica-Laurentia juxtaposition within the Rodinia supercontinent

The positions of Laurentia and other landmasses in the Precambrian supercontinent of Rodinia are controversial. Although geological and isotopic data support an East Antarctic fit with western Laurentia, alternative reconstructions favor the juxtaposition of Australia, Siberia, or South China. New geologic, age, and isotopic data provide a positive test of the juxtaposition with East Antarctica: Neodymium isotopes of Neoproterozoic rift-margin strata are similar; hafnium isotopes of approximately 1.4-billion-year-old Antarctic-margin detrital zircons match those in Laurentian granites of similar age; and a glacial clast of A-type granite has a uraniun-lead zircon age of approximately 1440 million years, an epsilon-hafnium initial value of +7, and an epsilon-neodymium initial value of +4. These tracers indicate the presence of granites in East Antarctica having the same age, geochemical properties, and isotopic signatures as the distinctive granites in Laurentia.     

Seasonal Oxygen Isotopic Variations in Living Planktonic Foraminifera off Bermuda

Seasonal variations in the oxygen-18/oxygen-16 ratio of calcite shells of living planktonic foraminifera in the Sargasso Sea off Bermuda are a direct function of surface water temperature. Seasonal occurrence as well as depth habitat are determining factors in the oxygen isotopic composition of planktonic foraminifera. These relationships may be used to determine the seasonal temperature contrast of oceans in the past.