Biomedical subjects

C Rücker

Publications and source records attributed to C Rücker.

7 recordsLinked to original sources

PubMed1992

[Long-term observation after percutaneous transluminal angioplasty in the pelvic and leg areas].

In this study 163 patients had long term follow ups after PTA; the value of a test which had previously hardly been used, the "Cox proportional hazards model", for prognostic purposes is stressed. In this test account is taken of the severity of the stenosis before PTA, the extent of re-stenosis following PTA and the distance of the occlusion from the aorta and these are related to the likelihood of success. The use of the Cox proportional hazards model with an accurate description of the clinical material and the use of the Kaplan-Meier method is recommended in order to obtain comparable figures for the results obtained in various centres. In this study patency after six months was 77%, after a year 67%, after three years 46% and after five years 37%.

Angioplasty, Balloon↗

PubMed1991

On using the adjacency matrix power method for perception of symmetry and for isomorphism testing of highly intricate graphs.

A modification of the adjacency matrix power method described recently for the perception of symmetry in graphs is introduced, which expands the limits of the method far beyond the realm of chemically interesting graphs. The procedure finds the automorphism partition even for intricate graphs without performing a tree search. The calculation effort increases with the problem size polynomially for all tested cases, including strongly regular graphs, two-level regular graphs, and graphs corresponding to balanced incomplete block designs (BIBD). An equally powerful computer program for testing isomorphism of graphs based on the adjacency matrix power method is introduced.

Chemical Phenomena↗

PubMed1976

[Ultrasonic diagnostic measures in ambulant internal medical patients (author's transl)].

Ultrasonic investigation with the rapid B picture is a non-invasive method of examination which does not distress the patient and has no contraindications. It provides the examiner with abundant additional information, it is quickly performed without preparation and is therefore particularly to be recommended in ambulant patients. Ultrasonic investigation is no competitor to angiography or scintigraphy, but should be called on as a "forefield" diagnostic method before invasive methods. The various diagnostic possibilities are illustrated with some examples.

Ambulatory Care↗

PubMedDate not supplied

On finding nonisomorphic connected subgraphs and distinct molecular substructures.

The problem of finding all nonisomorphic subgraphs of a given graph (all distinct substructures of a given molecular structure) is discussed. A computer program is introduced that first generates all connected subgraphs and then uses a combination of well-discriminating graph invariants to eliminate duplicates. The program is broadly applicable, in particular for molecular graphs which may or may not contain unsaturation or heteroatoms. The number of distinct substructures (Ns), proposed earlier as a measure of a compound's complexity which takes into account its symmetry, is thus automatically obtained. As was to be expected, due to the nature of the problem the computational effort increases exponentially with problem size, whence in most cases complexity measures other than Ns are to be preferred.

Journal Article↗

PubMedDate not supplied

Using protochirons for three-dimensional coding of certain chemical structures.

For three-dimensional coding (including enantiomerism) of staggered paths and circuits on the diamond lattice, or paths/circuits with angles 90 degrees or 180 degrees on the cubic lattice, use is made of the previously defined paths-3 (paths of length three bonds defining two intersecting planes). The two cases mentioned above are examined and exemplified. In the diamond lattice there are three kinds of diamond-paths-3: one is achiral (Z) and two are chiral and enantiomeric (R and S). In the cubic lattice there are six kinds of orthopaths-3, of which only two are chiral and enantiomeric (R and S) and four are achiral (I, L, U, and Z). The chiral paths-3 are the previously defined protochirons in the respective lattice. Coding ascribes to each bond the letter that would characterize it if it were the central bond of an isolated path-3. To obtain a unique code out of several equally correct ones it is proposed to use the convention of inverse alphabetic priority in the above system of letters.

Journal Article↗

PubMedDate not supplied

On walks in molecular graphs.

Walks in molecular graphs and their counts for a long time have found applications in theoretical chemistry. These are based on the fact that the (i, j)-entry of the kth power of the adjacency matrix is equal to the number of walks starting at vertex i, ending at vertex j, and having length k. In recent papers (refs 13, 18, 19) the numbers of all walks of length k, called molecular walk counts, mwc(k), and their sum from k = 1 to k = n - 1, called total walk count, twc, were proposed as quantities suitable for QSPR studies and capable of measuring the complexity of organic molecules. We now establish a few general properties of mwc's and twc among which are the linear dependence between the mwc's and linear correlations between the mwc's and twc, the spectral decomposition of mwc's, and various connections between the walk counts and the eigenvalues and eigenvectors of the molecular graph. We also characterize the graphs possessing minimal and maximal walk counts.

Journal Article↗

PubMedDate not supplied

Substructure, subgraph, and walk counts as measures of the complexity of graphs and molecules.

In discussions of unsaturated compounds represented by multigraphs it is necessary to distinguish between the notions of substructure and subgraph. Here the difference is explained and exemplified, and a computer program is introduced which for the first time is able to construct and count all substructures and subgraphs for a colored multigraph (a molecular compound which may contain unsaturation and heteroatoms). Construction of all substructures and subgraphs is computationally demanding; therefore, two alternatives are pointed out for the treatment of large sets of compounds: (i) Often it will suffice to consider counts of substructures/subgraphs up to a certain number of edges only, information which is provided by the program much more rapidly. (ii) It is shown that information equivalent to that gained from substructure or subgraph counts is often far more easily available using walk counts. Some problems and their consequences for substructure/subgraph/walk counts are discussed that arise from the models used in organic chemistry for certain compounds such as aromatics and from the necessity to express qualitative features of molecular structures numerically.

Journal Article↗