Biomedical subjects

J Tromp

Publications and source records attributed to J Tromp.

3 recordsLinked to original sources

PubMed1999

Normal-mode and free-Air gravity constraints on lateral variations in velocity and density of Earth's mantle

With the use of a large collection of free-oscillation data and additional constraints imposed by the free-air gravity anomaly, lateral variations in shear velocity, compressional velocity, and density within the mantle; dynamic topography on the free surface; and topography on the 660-km discontinuity and the core-mantle boundary were determined. The velocity models are consistent with existing models based on travel-time and waveform inversions. In the lowermost mantle, near the core-mantle boundary, denser than average material is found beneath regions of upwellings centered on the Pacific Ocean and Africa that are characterized by slow shear velocities. These anomalies suggest the existence of compositional heterogeneity near the core-mantle boundary.

Journal Article↗

PubMed1996

On the nearest neighbour interchange distance between evolutionary trees.

We present some new results on a well-known distance measure between evolutionary trees. The trees we consider are free 3-trees having n leaves labeled 0,...,n - 1 (representing species), and n - 2 internal nodes of degree 3. The distance between two trees is the minimum number of nearest neighbour interchange (NNI) operations required to transform one into the other. First, we improve an upper bound on the nni-distance between two arbitrary n-node trees from 4n log n (Culik & Wood, 1982, Inf. Pro. Letts. 15, 39-42) to n log n. Second, we present a counterexample disproving several theorems in (Waterman & Smith, 1978, J. theor. Biol. 73, 789-800). Roughly speaking, finding an equal partition between two trees does not imply decomposability of the distance finding problem. Third, we present a polynomial-time approximation algorithm that, given two trees, finds a transformation between them of length O(log n) times their distance. We also present some results of computations we performed on small size trees.

Algorithms↗

PubMed1979

Reduction of ferricytochrome c, methemoglobin and metmyoglobin by hydroxyl and alcohol radicals.

We have studied the reaction of ferricytochrome c, methemoglobin and metmyoglobin with OH and alcohol radicals (methanol, ethanol, ethylene glycol and glycerol). These radicals can be divided into three groups: 1. The OH radicals which reduce the ferricytochrome c with a yield of (30 +/- 10)% and methemoglobin with a yield of (40 +/- 10)%. They do not reduce metmyoglobin. The reduction is not a normal bimolecular reaction but is most probably an intramolecular electron transfer of a protein radical. 2. Methanol and ethanol radicals which reduce all three hemoproteins with a yield of (100 +/- 5)%. This reduction is a normal bimolecular reaction. 3. Glycerol radicals which do not reduce the ferrihemoproteins under our experimental conditions. Ethylene glycol radicals do not reduce ferricytochrome c and metmyoglobin but they do reduce methemoglobin with a yield of (30 +/- 10)%.

Alcohols↗