Biomedical subjects

Chun-Chung Chen

Publications and source records attributed to Chun-Chung Chen.

4 recordsLinked to original sources

PubMed2002

Cohesion-induced deepening transition of avalanches.

A directed avalanche model with a control parameter is introduced to describe the transition between cohesive and noncohesive granular material. The underlying dynamics of the process can be mapped to interface growth model. In that representation, a continuous phase transition separates the rough phase and the flat phase. In the avalanche formulation, this corresponds to a transition from deep to shallow avalanches. The scaling exponents of the avalanches indeed follow those of the underlying interface growth in both phases and at the transition point. However, the mass hyperscaling relation is broken at the transition point due to the fractal nature of the avalanche and a hierarchy of critical directed percolation processes.

Journal Article↗

PubMed2002

Directed avalanche processes with underlying interface dynamics.

We describe a directed avalanche model; a slowly unloading sandbox driven by lowering a retaining wall. The directness of the dynamics allows us to interpret the stable sand surfaces as world sheets of fluctuating interfaces in one lower dimension. In our specific case, the interface growth dynamics belongs to the Kardar-Parisi-Zhang (KPZ) universality class. We formulate relations between the critical exponents of the various avalanche distributions and those of the roughness of the growing interface. The nonlinear nature of the underlying KPZ dynamics provides a nontrivial test of such generic exponent relations. The numerical values of the avalanche exponents are close to the conventional KPZ values, but differ sufficiently to warrant a detailed study of whether avalanche-correlated Monte Carlo sampling changes the scaling exponents of KPZ interfaces. We demonstrate that the exponents remain unchanged, but that the traces left on the surface by previous avalanches give rise to unusually strong finite-size corrections to scaling. This type of slow convergence seems intrinsic to avalanche dynamics.

Journal Article↗

PubMed2002

Interface view of directed sandpile dynamics.

We present a directed unloading sand-box-type avalanche model, driven by slowly lowering the retaining wall at the bottom of the slope. The avalanche propagation in the two-dimensional surface is related to the space-time configurations in one-dimensional Kardar-Parisi-Zhang (KPZ) interface growth. We relate the scaling exponents of the avalanche cluster distribution to those for the growing surface. The numerical results are close but deviate significantly from the exact KPZ values. This might reflect stronger than usual corrections to scaling or be more fundamental, due to correlations between subsequent space-time interface configurations.

Journal Article↗

PubMed2002

Spinal epidural lipomatosis.

Epidural lipomatosis is an uncommon disorder defined as a pathologic overgrowth of normal epidural fat. It is most often associated with administration of exogenous steroids of variable duration and dose. However, it can occur in the absence of exposure to steroids. We report two cases of spinal epidural lipomatosis following more than 20 years of steroid use due to asthma. Pathologic compression fracture due to osteoporosis and acute cord compression syndrome were found in these 2 cases. After emergent decompressive laminectomy and fusion surgery, neurological function recovered. From a review of literature, most patients received decompressive laminectomy surgery. But in our additional cases, we performed decompressive laminectomy and fusion surgery which might prevent further spinal deformity and improve the spinal stability, then patients' symptoms subsided completely. Therefore, decompression surgery and fusion surgery may be necessary in patients with symptomatic spinal epidural lipomatosis with compression fracture.

Adrenal Cortex Hormones↗