Evaluation of Radiation Resistance of Polystyrene Using Molecular Dynamics Simulation.

The scission rates of polystyrene and fluorinated polystyrene irradiated in an irradiation facility with Co-60 γ-rays were determined using molecular dynamics simulation and gel permeation chromatography (GPC) molecular weight distributions. The prediction was based on the assumption that γ-ray energy is transferred to the initial velocity of the primary knock-on atom. We employed a molecular dynamics simulation procedure to compute the changes in bond length between the connections for selected values of the absorbed dose and compared the calculated values with measurements made on the irradiated samples. The samples were exposed to four different absorbed doses of 25, 50, 75, and 100 kGy. The scission process and scission ratio were simulated with LAMMPS with ReaxFF potential for each bond, and we compared the simulation results with the experimental data especially measuring average molecular weight to evaluate the effect of fluorination on radiation enhancement.

Preliminary Study on the Simulation of a Radiation Damage Analysis of Biodegradable Polymers.

In this study, biodegradable poly(L-lactide-co-ε-caprolactone) (PLCL) and poly(L-co-d,l lactide) (PLDLA) were evaluated using Geant4 (G4EmStandardPhysics_option4) for damage simulation, in order to predict the safety of these biodegradable polymers against gamma ray sterilization. In the PLCL damage model, both chain scission and crosslinking reactions appear to occur at a radiation dose in the range 0-200 kGy, but the chain cleavage reaction is expected to be relatively dominant at high irradiation doses above 500 kGy. On the other hand, the PLDLA damage model predicted that the chain cleavage reaction would prevail at the total irradiation dose (25-500 kGy). To verify the simulation results, the physicochemical changes in the irradiated PLCL and PLDLA films were characterized by GPC (gel permeation chromatography), ATR-FTIR (attenuated total reflection Fourier transform infrared), and DSC (difference scanning calorimetry) analyses. The Geant4 simulation curve for the radiation-induced damage to the molecular weight was consistent with the experimentally obtained results. These results imply that the pre-simulation study can be useful for predicting the optimal irradiation dose and ensuring material safety, particularly for implanted biodegradable materials in radiation processing.

Kikuchi-Fujimoto disease with prolonged fever in children.

We reviewed 12 patients who had Kikuchi-Fujimoto disease (KFD) and presented with prolonged fever and lymphadenopathy. The clinical and laboratory aspects of the patients confirmed by excisional lymph node biopsy were analyzed. The mean age of the children was 11.0 +/- 3.0 years (range: 6-15 years). The male-to-female ratio was 1.4:1. The median duration of fever before admission and the total duration of fever was 13 days (range: 7-65 days) and 19.5 days (range: 9-75 days), respectively. One patient had supraclavicular lymphadenopathy, 10 had cervical involvement, and 1 had axillary lymphadenopathy. All of the histologic findings of the lymph node biopsies showed the characteristic findings consistent with KFD, such as paracortical necrosis with karyorrhexis and an increase in the number of phagocytic histiocytes and atypical lymphocytes. As for the laboratory findings, leukopenia (3600 +/- 900 per mm3), anemia (hemoglobin 11.4 +/- 1.2 g/dL), an elevated erythrocyte sedimentation rate (44 +/- 18 mm/hour), and a relatively low C-reactive protein level (1.3 +/- 1.1 mg/dL) were noted. Eight patients received conservative therapy with antipyretics, and 3 patients were treated with prednisolone. KFD is a rare disease yet should be considered in the differential diagnosis for older children with prolonged fever and lymphadenopathy.