Temperature dependent giant resistance anomaly in LaAlO3/SrTiO3 nanostructures.

The resistance of the electron gas (2DEG) at the interface between the two band insulators LaAlO3 (LAO) and SrTiO3 (STO) typically drops monotonically with temperature and R/T curves during cooling and warm-up look identical for large area structures. Here we show that if the LAO/STO is laterally restricted by nanopatterning the resistance exhibits a temperature anomaly. Warming up nanostructures from low temperatures leads to one or two pronounced resistance peaks between 50 and 100 K not observed for larger dimensions. During cool-down current filaments emerge at the domain walls that form during a structural phase transition of the STO substrate. During warm-up the reverse phase transition can interrupt filaments before the sheet conductivity which dominates at higher temperature is reestablished. Due to the limited number of filaments in a nanostructure this process can result in a complete loss of conductance. As a consequence of these findings the transport physics extracted from experiments in small and large area LAO/STO structures may need to be reconsidered.

Development of a simple chromatographic method for the determination of piracetam in human plasma and its pharmacokinetic evaluation.

OBJECTIVE: The objective of study was to develop an accurate and reproducible HPLC method for determination of piracetam in human plasma and to evaluate pharmacokinetic parameters of 800 mg piracetam. METHODS: A simple, rapid, accurate, precise and sensitive high pressure liquid chromatography method has been developed and subsequently validated for determination of piracetam. This study represents the results of a randomized, single-dose and single-period in 18 healthy male volunteers to assess pharmacokinetic parameters of 800 mg piracetam tablets. Various pharmacokinetic parameters were determined from plasma for piracetam and found to be in good agreement with previous reported values. The data was analyzed by using Kinetica® version 4.4 according to non-compartment model of pharmacokinetic analysis and after comparison with previous studies, no significant differences were found in present study of tested product. RESULTS: The major pharmacokinetic parameters for piracetam were as follows: t1/2 was (4.40 ± 0.179) h; Tmax value was (2.33 ± 0.105) h; Cmax was (14.53 ± 0.282) µg/mL; the AUC(0-∞) was (59.19 ± 4.402) µg · h/mL. AUMC(0-∞) was (367.23 ± 38.96) µg. (h)(2)/mL; Ke was (0.16 ± 0.006) h; MRT was (5.80 ± 0.227) h; Vd was (96.36 ± 8.917 L). CONCLUSIONS: A rapid, accurate and precise high pressure liquid chromatography method was developed and validated before the study. It is concluded that this method is very useful for the analysis of pharmacokinetic parameters, in human plasma and assured the safety and efficacy of piracetam, can be effectively used in medical practice.

Frequency, presentation and postintervention prognosis of chondroblastoma.

OBJECTIVE: To evaluate the frequency of clinico-radiological presentation and the prognosis after treatment of chondroblastoma. DESIGN: A descriptive, observational study. PLACE AND DURATION OF STUDY: The study was carried out at the Department of Orthopaedic Surgery, JPMC, Karachi over the period of 16 years, January 1986 to June 2002. METHODOLOGY: Patients in teenage, presenting with signs and symptoms of a primary bone tumours, were included by retrospectively reviewing the tumour registry record. Detailed scrutiny of clinical record was carried out to analyze the clinico-radiological presentation and posttreatment prognosis criteria of healing was symptom-free centripetal and homogeneous ossification. RESULTS: Seven (1.24%) out of 563 primary bone tumour cases were chondroblastoma. The clinico-radiological presentation in the 2 out of 7 (28.57%) cases was classical, 2 simulated osteomyelitis and other 3 as chondromyxoid fibroma, aneurysmal bone cyst and giant cell tumour. Lesions were treated with curettage and bone grafting. One patient (14.28%) developed recurrence within 2 years after curettage and healed after re-curettage and bone grafting. Five out of 7 (71.42%) tumours showed good response and 2 out of 7 (28.57%) showed satisfactory response. CONCLUSION: Chondroblastoma is very rare benign primary bone tumour with high local recurrence rate. The lesions confined to epiphysis of weight-bearing bone present early with symptoms of mild arthritis. Lesions in non-weight-bearing bones often present late and simulates epiphysio-metaphyseal tumours. Lesions heals with centripetal healing and need more than 2 years follow-up to achieve recurrence-free healing.

Renal artery stenosis in renal transplantation presentation and management.

A review of the angioplasty records between 1990 and 1995 at the King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia revealed ten cases of transplant renal artery stenosis (RAS). The diagnosis in these cases was confirmed by renal angiography and all were treated by angioplasty. All study patients presented with uncontrolled hypertension in spite of multiple medications; eight had renal functional impairment and two patients had recurrent unexplained pulmonary edema in addition. Six patients had undergone end-to-end anastomosis, while four had end-to-side anastomosis of the artery during transplantation. Four had cadaveric renal transplants and six had living donor renal transplants. Eight of these patients responded well to angioplasty with marked improvement in their renal function and reduction in the number of anti-hypertensive medications. In one patient, it was not possible to pass the catheter through the stenosis and the patient underwent surgical reconstruction, while in another patient there were multiple stenotic lesions involving the external iliac and the transplant renal arteries suggesting atherosclerotic changes. We conclude that renal artery stenosis should be suspected in patients after renal transplant if they have uncontrolled or worsening hypertension, unexplained renal impairment or presentation with unexplained recurrent pulmonary edema. Renal angiography should be considered as part of the investigation of hypertension in renal transplant patients, and if the RAS is confirmed, angioplasty should be the procedure of choice.