For decades, developmental research has involved the study of sex differences in language acquisition. Many studies of these differences have found a slight advantage in competence for females early in life that seems to wane with age. However, because most of these studies have focused on sex differences in mean values, they have mostly neglected sex differences in variance with males being more variable. In the current study, we examined sex differences in language competence in terms of mean values and variance in large samples (N > 10,000) of German children aged 3-6 years. We administered several tests to assess the children's vocabulary, grammar, speech comprehension, pronunciation, and the processing of sentences and nonce words. Girls performed better than boys in all domains, most often to a statistically significant degree, although the effect sizes were small. Differences decreased with age. Boys varied significantly more than girls in their language competence. In response, we discuss explanations for these findings, as well as recommend directions for future research.

Starting about 1920 it becomes easier to track the growth of bearing materials technology. Until 1955, with few exceptions, comparatively little progress was made in this area. AISI 52100 and some carburising grades (AISI 4320, AISI 9310) were adequate for most applications. The catalyst to quantum advances in high-performance rolling-element bearing steels was the advent of the aircraft gas turbine engine. With improved bearing manufacturing and steel processing together with lubrication technology, the potential improvements in bearing life can as much as 80 times that attainable in the late 1950s or as much as 400 times that attainable in 1940. This paper summarises the chemical, metallurgical and physical aspects of bearing steels and their effect on rolling bearing life and reliability: the single most important variable that has significantly increased bearing life and reliability is vacuum processing of bearing steel. Differences between through hardened, case carburised and corrosion resistant steels are discussed. The interrelation of alloy elements and carbides and their effect on bearing life are presented. An equation relating bearing life, steel hardness and temperature is given. Life factors for various steels are suggested and discussed. A relation between compressive residual stress and bearing life is presented. The effects of retained austenite and grain size are discussed.

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Nearly five decades have passed since G. Lundberg and A. Palmgren published their life theory in 1947 and 1952 and it was adopted as an ANSIIABMA and ISO standard in 1950 and 1953. Subsequently, many variations and deviations from their life theory have been proposed, the most recent being that of E. Ioannides and T.A. Harris in 1985. This paper presents a critical analysis comparing the results of different life theories and discussing their implications in the design and analysis of rolling-element bearings. Variations in the stresslife relation and in the critical stress related to bearing life are discussed using stress fields obtained from three-dimensional, finite-element analysis of a ball in a nonconforming race under varying load. The results showed that for a ninth power stress-life exponent the Lundberg-Palmgren theory best predicts life as exhibited by most air-melted bearing steels. For a 12th power relation reflected by modem bearing steels, a Zaretsky-modified Weibull equation is superior. The assumption of a fatigue-limiting stress distorts the stress-life exponent and overpredicts life. in-plane shear stress, Pa (psi)