Kurt Liffman

Aluminum-Magnesium and Oxygen Isotope Study of Relict Ca-Al-rich Inclusions in Chondrules

Relict Ca-Al-rich inclusions (CAIs) in chondrules crystallized before their host chondrules and were subsequently partly melted together with chondrule precursors during chondrule formation. Like most CAIs, relict CAIs are 16O enriched (Δ17O -9‰). Hibonite in a relict CAI from the ungrouped carbonaceous chondrite Adelaide has a large excess of radiogenic 26Mg (26Mg*) from the decay of 26Al, corresponding to an initial 26Al/27Al ratio [(26Al/27Al)I] of (3.7 ± 0.5) × 10-5; in contrast, melilite in this CAI and plagioclase in the host chondrule show no evidence for 26Mg* [(26Al/27Al)I of <5 × 10-6]. Grossite in a relict CAI from the CH carbonaceous chondrite PAT 91546 has little 26Mg*, corresponding to a (26Al/27Al)I of (1.7 ± 1.3) × 10-6. Three other relict CAIs and their host chondrules from the ungrouped carbonaceous chondrite Acfer 094, CH chondrite Acfer 182, and H3.4 ordinary chondrite Sharps do not have detectable 26Mg* [(26Al/27Al)I < 1 × 10-5, <(4-6) × 10-6, and <1.3 × 10-5, respectively]. Isotopic data combined with mineralogical observations suggest that relict CAIs formed in an 16O-rich gaseous reservoir before their host chondrules, which originated in an 16O-poor gas. The Adelaide CAI was incorporated into its host chondrule after 26Al had mostly decayed, at least 2 Myr after the CAI formed, and this event reset 26Al-26Mg systematics.

Development of optimized vascular fractal tree models using level set distance function

Using the concepts of fractal scaling and constrained constructive optimization (CCO), a branching tree model, which has physiologically meaningful geometric properties, can be constructed. A vascular branching tree model created in this way, although statistically correct in representing the vascular physiology, still does not possess a physiological correct arrangement of the major arteries. A distance-function based technique for staged growth of vascular models has been developed in this work to address this issue. Time-dependent constraints based on a signed-distance level set function have been added, so that the tree models will first be grown near the designated surface(s) and, then, gradually allowed to penetrate into the enclosed volume. The proposed technique has been applied to construct a model of the human cerebral vasculature, which is characterized by the above-mentioned distribution of the arteries.

The stellar-disk electric (short) circuit: observational predictions for a YSO jet flow

AbstractnWe discuss the star-disk electric circuit for a young stellar object (YSO) and calculate the expected torques on the star and the disk. We obtain the same disk magnetic field and star-disk torques as given by standard magnetohydrodynamic (MHD) analysis. We show how a short circuit in the star-disk electric circuit may produce a magnetically-driven jet flow from the inner edge of a disk surrounding a young star.nnAn unsteady bipolar jet flow is produced that flows perpendicular to the disk plane. Jet speeds of order hundreds of kilometers per second are possible, while the outflow mass loss rate is proportional to the mass accretion rate and is a function of the disk inner radius relative to the disk co-rotation radius.n

Transport by pulsatile flow in a branching network of cerebral vasculature

The supply of oxygen and glucose by blood flow is vital to the normal function of the brain and the deficit of either of these metabolism elements can cause severe degradation of the brain functionality. The transport of materials in the complex multi-branching structure of the cerebral vasculature is investigated to predict brain oxygenation under normal conditions. A mathematical model of material transport due to pulsatile flow in a complex dichotomous branching tree network was developed which incorporated material-geometry interaction and diffusion across the blood vessel wall. Unlike previous work, this modelling work includes the full network structure and incorporates time-dependent flow. The predicted results indicate some effect of the flow transients on the propagation of the material introduced at the root segment in the vascular network. The effect was more pronounced in the case of constant blood viscosity. The transport model addressed the issue of oxygen transport in the cerebral vascular branching network with the inclusion of red blood cell (RBC) separation at bifurcation points. The predicted results indicate the significance of the vascular network geometry and RBC-bifurcation point interaction in defining the homogeneity of flow and oxygenation by the fractal vasculature. The simulations are found to be able to provide insights into the transport of materials by the blood circulation in the cerebral vasculature and the various factors which