Although humans have been exposed to airborne nanosized particles (NSPs; < 100 nm) throughout their evolutionary stages, such exposure has increased dramatically over the last century due to anthropogenic sources. The rapidly developing field of nanotechnology is likely to become yet another source through inhalation, ingestion, skin uptake, and injection of engineered nanomaterials. Information about safety and potential hazards is urgently needed. Results of older bio-kinetic studies with NSPs and newer epidemiologic and toxicologic studies with airborne ultrafine particles can be viewed as the basis for the expanding field of nanotoxicology, which can be defined as safety evaluation of engineered nanostructures and nanodevices. Collectively, some emerging concepts of nanotoxicology can be identified from the results of these studies. When inhaled, specific sizes of NSPs are efficiently deposited by diffusional mechanisms in all regions of the respiratory tract. The small size facilitates uptake into cells and transcytosis across epithelial and endothelial cells into the blood and lymph circulation to reach potentially sensitive target sites such as bone marrow, lymph nodes, spleen, and heart. Access to the central nervous system and ganglia via translocation along axons and dendrites of neurons has also been observed. NSPs penetrating the skin distribute via uptake into lymphatic channels. Endocytosis and biokinetics are largely dependent on NSP surface chemistry (coating) and in vivo surface modifications. The greater surface area per mass compared with larger-sized particles of the same chemistry renders NSPs more active biologically. This activity includes a potential for inflammatory and pro-oxidant, but also antioxidant, activity, which can explain early findings showing mixed results in terms of toxicity of NSPs to environmentally relevant species. Evidence of mitochondrial distribution and oxidative stress response after NSP endocytosis points to a need for basic research on their interactions with subcellular structures. Additional considerations for assessing safety of engineered NSPs include careful selections of appropriate and relevant doses/concentrations, the likelihood of increased effects in a compromised organism, and also the benefits of possible desirable effects. An interdisciplinary team approach (e.g., toxicology, materials science, medicine, molecular biology, and bioinformatics, to name a few) is mandatory for nanotoxicology research to arrive at an appropriate risk assessment.

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Nanotoxicology: An Emerging Discipline Evolving from Studies of Ultrafine Particles

Summary
The classic, multivariate technique of principal component analysis can be used to find and estimate the directions of lines and planes of best least-squares fit along the demagnetization path of a palaeomagnetic specimen, thereby replacing vector subtraction, remagnetization circles and difference vector paths with one procedure. Eigenvalues from the analysis are the variance of the data along each principal axis, and provide a relative measure of collinearity or coplanarity which may be used to define a general palaeomagnetic precision index. Demagnetization planes found with principal component analysis may be used in place of difference vector paths for locating Hoffman—Day directions, avoiding unnecessary vector subtraction and intensity truncation steps. Two methods are discussed for jointly estimating an average remanence direction from demagnetization lines and planes.

The least-squares line and plane and the analysis of palaeomagnetic data

Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations

/pdf/global-continental-and-ocean-basin-reconstructions-since-200-huopwd2ldv.pdf

Global continental and ocean basin reconstructions since 200 Ma

Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of eastern Tethys

Hysteresis properties of titanomagnetites: Grain-size and compositional dependence

It is demonstrated that the stability against af demagnetization of TRM carried by multidomain magnetite increases with increasing strength of the inducing field. This multidomain field-dependence trend of stability against af demagnetization is opposite to that of single-domain particles. A simple test to distinguish multidomain and single-domain carriers of remanence is designed that makes use of the distinctive af demagnetization characteristics. The test was applied to a variety of igneous rocks. None of these showed truly multidomain characteristics. Thus, although some TRM is undoubtedly multidomain in these rocks, the TRM is dominated by single-domain carriers. These results are consistent with the growing evidence of the importance of very fine grained magnetite as a carrier of NRM in many igneous rocks.

On the alternating field demagnetization characteristics of multidomain thermoremanent magnetization in magnetite

Although immunosuppressant immunophilin ligands promote neurite outgrowth in vitro, their neurotrophic activities are clearly independent of their immunosuppressive activity. In the present report, a novel nonimmunosuppressive immunophilin ligand, GPI-1046 (3-(3-pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarboxylate) is described. In vitro, GPI-1046 bound to FK506 binding protein-12 and elicited neurite outgrowth from sensory neuronal cultures with picomolar potency with maximal effects comparable to nerve growth factor. In vivo, GPI-1046 stimulated the regeneration of lesioned sciatic nerve axons and myelin levels. In the central nervous system, GPI-1046 promoted protection and/or sprouting of serotonin-containing nerve fibers in somatosensory cortex following parachloroamphetamine treatment. GPI-1046 also induced regenerative sprouting from spared nigrostriatal dopaminergic neurons following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity in mice or 6-hydroxydopamine (6-OHDA) toxicity in rats. The rotational abnormality in 6-OHDA treated rats was alleviated by GPI-1046. These neurotrophic actions in multiple models suggest therapeutic utility for GPI-1046 in neurodegenerative diseases.

http://www.pnas.org/content/94/5/2019.full.pdf

Neurotrophic immunophilin ligands stimulate structural and functional recovery in neurodegenerative animal models

Polar wander paths for the North and South China blocks suggest that (1) both were parts of Gondwana in the Palaeozoic, (2) the North China block accreted to Siberia in the late Permian and (3) the South China block accreted to the North China block in the middle Triassic to the early Jurassic. Comparison of the polar wander path for the South China block with that for northern Eurasia suggests that relative motion of over 4,000 km has occurred between them.

Michael D Fuller

Papers

Hysteresis properties of titanomagnetites: Grain-size and compositional dependence

On the alternating field demagnetization characteristics of multidomain thermoremanent magnetization in magnetite

Neurotrophic immunophilin ligands stimulate structural and functional recovery in neurodegenerative animal models

Preliminary Phanerozoic polar wander paths for the North and South China blocks

Geomagnetic reversal paths