Lifetime of anode polymer in magnetically insulated ion diodes for high-intensity pulsed ion beam generation.

Generation of high-intensity pulsed ion beam (HIPIB) has been studied experimentally using polyethylene as the anode polymer in magnetically insulated ion diodes (MIDs) with an external magnetic field. The HIPIB is extracted from the anode plasma produced during the surface discharging process on polyethylene under the electrical and magnetic fields in MIDs, i.e., high-voltage surface breakdown (flashover) with bombardments by electrons. The surface morphology and the microstructure of the anode polymer are characterized using scanning electron microscopy and differential scanning calorimetry, respectively. The surface roughening of the anode polymer results from the explosive release of trapped gases or newly formed gases under the high-voltage discharging, leaving fractured surfaces with bubble formation. The polyethylene in the surface layer degrades into low-molecular-weight polymers such as polyethylene wax and paraffin under the discharging process. Both the surface roughness and the fraction of low molecular polymers apparently increase as the discharging times are prolonged for multipulse HIPIB generation. The changes in the surface morphology and the composition of anode polymer lead to a noticeable decrease in the output of ion beam intensity, i.e., ion current density and diode voltage, accompanied with an increase in instability of the parameters with the prolonged discharge times. The diode voltage (or surface breakdown voltage of polymer) mainly depends on the surface morphology (or roughness) of anode polymers, and the ion current density on the composition of anode polymers, which account for the two stages of anode polymer degradation observed experimentally, i.e., stage I which has a steady decrease of the two parameters and stage II which shows a slow decrease, but with an enhanced fluctuation of the two parameters with increasing pulses of HIPIB generation.

[Study on the construction of standard D1S549 allelic ladder via molecular cloning and its genetic polymorphism in Chinese three populations].

OBJECTIVE: To resolve the problem of the accuracy and standardization of STR-PCR typing in forensic practice, we have designed a new method to produce standard D1S549 allelic ladder. METHODS: Eight different PCR amplified D1S549 allelic fragments were isolated from the gel, eluted into the distilled water and re-amplified by PCR. The purified allelic fragments were then blunt-end subcloned individually into the pUC plasmid vectors and transfected into competent E. coli DH5 alpha cells. RESULTS: The sequencing results confirmed that the size and the construe of the inserts were correct. The recombinant plasmids DNA with 8 inserts were then used as templates for re-amplification to generate D1S549 standard ladder, with which the genetic polymorphisms of D1S549 locus in Chinese Han population in chengdu, Hui population in Gansu and Wei population in Xinjiang were studied. CONCLUSION: The results showed that the standard ladder made via this method is excellent, and D1S549 locus is robust for genetic research and forensic application.

[Short tandem repeat loci examination after repair of coracoclavicular ligament injury by tissue engineered tendon].

OBJECTIVE: To evaluate the result of clinical application in the repair of coracoclavicular ligament injury by tissue engineered tendon using the technique of short tandem repeat loci examination. METHODS: In september 1999, human embryonic tendon cells and artificial materials were co-cultured in vitro to construct tissue engineered tendon, which repaired coracoclavicular ligament injury. After 6 months of operation, micro-tissue were sampled during the operation of removal of internal fixation, and morphological characteristics were examined by HE staining, DNA of tissues were extracted to examine D3S1754 and Cyar04 gene loci. RESULTS: The shoulder function of the patient was recovered well after operation, and no local or systemic immunological rejection were occurred. The electrophoresis typing showed 13/14 at D3S1754 and 8/9 at Cyar04 in the tissue of tissue engineered tendon, while the autogenous ligament were 13/13 and 8/8 at D3S1754 and Cyar04 loci respectively, which suggested that the tissue engineered tendon was survived in vivo. CONCLUSION: The examination of short tandem repeat loci is a better index to evaluate the survival situation of tissue engineered tissue after transplantation in clinical application.

[Allele and genotype frequency distribution of D19S400 locus in several populations].

Using polymerase chain reaction and PAG electrophoresis, D19S400 Locus was investigated in the populations of Chinese, Germany, Slovakian, and American Black Population. 620 samples collected from the four populations were tested and a total of 11 alleles (*7 to *17) and 47 genotypes were found. The heterozygosity was observed between 0.78 and 0.88, and the discriminating power was between 0.9385 and 0.9664. The distributions of genotypes in the four populations were in accordance with Hardy-Weinberg equilibrium. Significant differences were observed in the distribution of allele frequencies among the three major racial populations (Mongoloid, Caucasian, Negroid). According to the results obtained in this study, D19S400 locus is a robust STR for forensic and genetic purposes.