Direct determination of three-phase contact line properties on nearly molecular scale.

Wetting phenomena in multi-phase systems govern the shape of the contact line which separates the different phases. For liquids in contact with solid surfaces wetting is typically described in terms of contact angle. While in macroscopic systems the contact angle can be determined experimentally, on the molecular scale contact angles are hardly accessible. Here we report the first direct experimental determination of contact angles as well as contact line curvature on a scale of the order of 1nm. For water nucleating heterogeneously on Ag nanoparticles we find contact angles around 15 degrees compared to 90 degrees for the corresponding macroscopically measured equilibrium angle. The obtained microscopic contact angles can be attributed to negative line tension in the order of -10(-10) J/m that becomes increasingly dominant with increasing curvature of the contact line. These results enable a consistent theoretical description of heterogeneous nucleation and provide firm insight to the wetting of nanosized objects.

Episodic Dynamics of Tar Spot of Annual Lespedeza Within and Among Years.

The temporal and spatial dynamics of six tar spot epidemics were examined at two sites in mid-Missouri during 1990 to 1992. The sites, 48 km apart, differed in topography (flat versus slope), soil texture (silt loam versus silty-clay loam), and cropping history (orchard versus row crops). Temporal dynamics of disease incidence differed more among years than between sites. During 1990, temporal dynamics of the two epidemics followed a classic monotonic increase, whereas disease increase was episodic for the four epidemics observed during 1991 and 1992. Disease increase was associated with shading of the plant canopy or with the presence of dodder. Disease increase was related inversely to intercepted photosynthetically active radiation. Taken together, these observations suggest that factors that increase shading in the lespedeza canopy also increase tar spot incidence. For only two of the six epidemics was there a significant relationship between disease incidence (proportion of leaflets diseased) and disease severity (proportion of leaflet area diseased), with disease severity rarely exceeding 10%. These observations suggest that relatively low tar spot incidence may result in significant leaf losses, which would reduce lespedeza hay quality and yield. Further, this study demonstrates the importance of experimental repetition in both space and time to fully appreciate the range of disease dynamics for a single pathosystem.

Osteoporosis, sedentary lifestyle, and increasing hip fractures: pathogenic relationship or differential survival bias.

Osteoporosis, although a disorder of antiquity, has become more prevalent in developed countries and is a major risk factor for skeletal fracture. Accordingly, the increasing incidence of hip fracture among the elderly within developed nations has been attributed to an increased prevalence of osteoporosis. An increasingly sedentary lifestyle has been suggested as a significant contributing factor for the increased prevalence of osteoporosis. However, differential survival, reflecting changing competing mortality risks, will alter the gene pool of a surviving population cohort. Thus, the gene pool (and hence, disease susceptibilities) of 70-year-old individuals in 1990, for example, should not implicitly be assumed to be the same as 70-year-old individuals in 1950. Consequently, differences in the prevalence of osteoporosis or incidence of hip fracture between current and past elderly cohorts do not necessarily imply differences in environmental risk factors such as levels of physical activity. Instead, variation in competing mortality risks over time may produce differential survival with selection bias and "naturally" lead to increases in the incidence and prevalence of some aging-related disorders such as osteoporosis.

Suicide in the United States, 1951-1988: constant age-period-cohort rates in 40- to 44-year-old men.

Age-specific suicide rates in the United States between 1951 and 1988 were shown in cohort, cross-sectional, and age group formats. Despite considerable variation among women and younger and older men, suicide rates among 40- to 44-year-old men have remained stable. Since suicide is strongly influenced by psychosocial stressors, the constant suicide rates in middle-aged men suggest a consistency in the stress experienced by this population subgroup.