Ward Processes Research Articles

Light-controlled morphological development of self-organizing bioinspired nanocomposites.

Nature's intricate biominerals inspire fundamental questions on self-organization and guide innovations towards functional materials. While advances in synthetic self-organization have enabled many levels of control, generating complex shapes remains difficult. Specifically, controlling morphologies during formation at the single micro/nanostructure level is the key challenge. Here, we steer the self-organization of barium carbonate nanocrystals and amorphous silica into complex nanocomposite morphologies by photogeneration of carbon dioxide (CO2) under ultraviolet (UV) light. Using modulations in the UV light intensity, we select the growth mode of the self-organization process inwards or outwards to form helical and coral-like morphologies respectively. The spatiotemporal control over CO2 photogeneration allows formation of different morphologies on pre-assigned locations, switching between different growth modes-to form for instance a coral on top of a helix or vice versa, and subtle sculpting and patterning of the nanocomposites during formation. These findings advance the understanding of these versatile self-organization processes and offer new prospects for tailored designs of functional materials using photochemically driven self-organization.

Progress of artificial carious lesions in enamel.

Progress of lesions with time is important from a practical point of view, but especially because it provides information on the mechanism of the caries process. Firstly, a theoretical description of lesion progress with time is derived. It is based on the assumption that (1) steady-state diffusion during the caries process takes place through very tiny holes in the enamel surface, (2) inhibitors make the enamel surface insoluble and diffuse during the process inwards (the inhibitors, e.g. diphosphonates or fluorides may be coming from an external solution or may orginate from the enamel itself), and (3) the inhibitor blocks enamel dissolution effectively if the inhibitor concentration XL exceeds the fraction of surface phosphate sites XL*. The theory shows that lesion depth (r1) is about proportional to the third root of demineralization time (t), and can be written as r13 = αt + q, α and q being constants. Second, a comparison is made with experimental lesion depth data from various authors in artifical lesion systems. The results show that lesion progress in human and bovine enamel at pH 4, 4.5 and 5 is very well described by the above formula. This result indicates strongly that inhibitor action and inhibitor penetration are important during the caries process. From the experimentally determined slope a the apparent diffusion coefficient Dapp of the process is determined as ≈ 10––5 cm2s––1. This value is comparable to D of Ca++ and phosphate ions in aqueous solutions and indicates that ion transport during the process takes place in water-filled channels.

THE MARINE DIATOM THALASSIOSIRA OESTRUPII: STRUCTURE, TAXONOMY AND DISTRIBUTION

Thalassiosira oestrupii (Ostenfeld) Hasle was studied from the southern Indian Ocean, Wed‐dell Sea, and northern Atlantic Ocean. It has the longer extension of the strutted process inwards, with three small columnar supports. A single strutted process near the central areola is 2‐3 areolae away from the single labiate process; both are usually visible in the light microscope. Two bands are septate: the valvocopula (intercalary band next to the mantle) is ribbed with a complex pattern of pores, while the other intercalary band (copula) present has but a single ring of large pores. T. oestrupii var. venrickae is described from warmer water with similar bands but with differences in areolae array and spacing of marginal strutted processes. It was found in the Gulf of Mexico, eastern and western Atlantic Ocean, Indian Ocean, and western Indian Ocean. The two varieties appear to differ in their ecology and distribution, with T. oestrupii var. oestrupii apparently a cosmopolitan oceanic taxon and T. oestrupii var. venrickae a tropical and subtropical continental shelf taxon.

The Marine Diatom Thalassiosira Oestrupii: Structure, Taxonomy and Distribution

Thalassiosira oestrupii (Ostenfeld) Hasle was studied from the southern Indian Ocean, Wed-dell Sea, and northern Atlantic Ocean. It has the longer extension of the strutted process inwards, with three small columnar supports. A single strutted process near the central areola is 2-3 areolae away from the single labiate process; both are usually visible in the light microscope. Two bands are septate: the valvocopula (intercalary band next to the mantle) is ribbed with a complex pattern of pores, while the other intercalary band (copula) present has but a single ring of large pores. T. oestrupii var. venrickae is described from warmer water with similar bands but with differences in areolae array and spacing of marginal strutted processes. It was found in the Gulf of Mexico, eastern and western Atlantic Ocean, Indian Ocean, and western Indian Ocean. The two varieties appear to differ in their ecology and distribution, with T. oestrupii var. oestrupii apparently a cosmopolitan oceanic taxon and T. oestrupii var. venrickae a tropical and subtropical continental shelf taxon.