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Biomedical subjects

H H Hsieh

Publications and source records attributed to H H Hsieh.

At least 19 recordsLinked to original sources
PubMed2006

Spin state transition in LaCoO3 studied using soft x-ray absorption spectroscopy and magnetic circular dichroism.

Using soft x-ray absorption spectroscopy and magnetic circular dichroism at the Co-L(2,3) edge, we reveal that the spin state transition in LaCoO3 can be well described by a low-spin ground state and a triply degenerate high-spin first excited state. From the temperature dependence of the spectral line shapes, we find that LaCoO3 at finite temperatures is an inhomogeneous mixed-spin state system. It is crucial that the magnetic circular dichroism signal in the paramagnetic state carries a large orbital momentum. This directly shows that the currently accepted low- or intermediate-spin picture is at variance. Parameters derived from these spectroscopies fully explain existing magnetic susceptibility, electron spin resonance, and inelastic neutron data.

Journal Article↗
PubMed2006

Transfer of spectral weight and symmetry across the metal-insulator transition in VO(2).

We present a detailed study of the valence and conduction bands of VO2 across the metal-insulator transition using bulk-sensitive photoelectron and O K x-ray absorption spectroscopies. We observe a giant transfer of spectral weight with distinct features that require an explanation which goes beyond the Peierls transition model as well as the standard single-band Hubbard model. Analysis of the symmetry and energies of the bands reveals the decisive role of the V 3d orbital degrees of freedom. Comparison to recent realistic many body calculations shows that much of the k dependence of the self-energy correction can be cast within a dimer model.

Journal Article↗
PubMed2006

Orbitally driven spin-singlet dimerization in S=1 La4Ru2O10.

Using x-ray absorption spectroscopy at the Ru-L2,3 edge we reveal that the Ru4+ ions remain in the S=1 spin state across the rare 4d-orbital ordering transition and spin-gap formation. We find using local spin density approximation + Hubbard U band structure calculations that the crystal fields in the low-temperature phase are not strong enough to stabilize the S=0 state. Instead, we identify a distinct orbital ordering with a significant anisotropy of the antiferromagnetic exchange couplings. We conclude that La4Ru2O10 appears to be a novel material in which the orbital physics drives the formation of spin-singlet dimers in a quasi-two-dimensional S=1 system.

Journal Article↗
PubMed2005

Orbital-assisted metal-insulator transition in VO2.

We found direct experimental evidence for an orbital switching in the V 3d states across the metal-insulator transition in VO2. We have used soft-x-ray absorption spectroscopy at the V L2,3 edges as a sensitive local probe and have determined quantitatively the orbital polarizations. These results strongly suggest that, in going from the metallic to the insulating state, the orbital occupation changes in a manner that charge fluctuations and effective bandwidths are reduced, that the system becomes more one dimensional and more susceptible to a Peierls-like transition, and that the required massive orbital switching can only be made if the system is close to a Mott insulating regime.

Journal Article↗
PubMed2005

Controlling orbital moment and spin orientation in CoO layers by strain.

We have observed that CoO films grown on different substrates show dramatic differences in their magnetic properties. Using polarization dependent x-ray absorption spectroscopy at the Co L2,3 edges, we revealed that the magnitude and orientation of the magnetic moments strongly depend on the strain in the films induced by the substrate. We presented a quantitative model to explain how strain together with the spin-orbit interaction determine the 3d orbital occupation, the magnetic anisotropy, as well as the spin and orbital contributions to the magnetic moments. Control over the sign and direction of the strain may, therefore, open new opportunities for applications in the field of exchange bias in multilayered magnetic films.

Journal Article↗
PubMed2005

Determination of the orbital moment and crystal-field splitting in LaTiO3.

Utilizing a sum rule in a spin-resolved photoelectron spectroscopic experiment with circularly polarized light, we show that the orbital moment in LaTiO3 is strongly reduced from its ionic value, both below and above the Ne el temperature. Using Ti L2,3 x-ray absorption spectroscopy as a local probe, we found that the crystal-field splitting in the t2g subshell is about 0.12-0.30 eV. This large splitting does not facilitate the formation of an orbital liquid.

Journal Article↗
PubMed2004

Different look at the spin state of Co(3+) ions in a CoO(5) pyramidal coordination.

Using soft-x-ray absorption spectroscopy at the Co L(2,3) and O K edges, we demonstrate that the Co3+ ions with the CoO5 pyramidal coordination in the layered Sr2CoO3Cl compound are unambiguously in the high spin state. Our result questions the reliability of the spin state assignments made so far for the recently synthesized layered cobalt perovskites and calls for a reexamination of the modeling for the complex and fascinating properties of these new materials.

Journal Article↗
PubMed2003

Magnetic dichroism and spin structure of antiferromagnetic NiO(001) films.

We find that Ni L2 edge x-ray magnetic linear dichroism is fully reversed for NiO(001) films on materials with reversed lattice mismatch. We relate this phenomenon to a preferential stabilization of magnetic S domains with main spin component either in or out of the plane, via dipolar interactions. This suggests a way to selectively control spin structures in 3d systems with small spin-orbit coupling.

Journal Article↗
PubMed2001

Emphysematous pyelonephritis in a renal allograft: successful treatment with percutaneous drainage and nephrostomy.

Emphysematous pyelonephritis in renal transplant allograft occurs rarely. This is a case report on a 55-year-old man who had renal transplantation in 1983 and developed post-transplant diabetes mellitus in 1984. This patient suffered from fever and right low abdominal pain and was subsequently diagnosed as emphysematous pyelonephritis by computerized tomography. He was successfully treated with percutaneous drainage, percutaneous nephrostomy and parenteral antibiotics. Although the management of emphysematous pyelonephritis has been a subject of controversy, we recommend consideration of renal preservation in patients with few risk factors, especially in those patients presenting with chronic renal insufficiency, solitary kidney and transplant allograft.

Combined Modality Therapy↗
PubMed2000

Retroperitoneoscopic ureterolithotomy for impacted ureteral stones.

BACKGROUND: Despite the fact that extracorporeal shock wave lithotripsy and endourological procedures have greatly diminished the need for open ureterolithotomy, invasive open surgery is still necessary in some cases of obstinate ureteral stones when less invasive methods fail. Since Wickham first performed a retroperitoneoscopic ureterolithotomy in 1979, procedures which are less invasive than open ureterolithotomy have been available in some selected cases. METHODS: In 1997, retroperitoneoscopic ureterolithotomy was performed in 5 patients with ureteral stones, in whom treatment with other minimally invasive procedures had failed. Using Gaur's technique of balloon dissection of the retroperitoneal space, retroperitoneoscopic ureterolithotomy was successfully performed in all cases. RESULTS: All the patients were treated successfully with the retroperitoneoscopic maneuver. The average operating time was 125 (90 to 175) minutes, and the average blood loss was 75 (20 to 200) ml. No patient required an analgesic injection postoperatively. The average postoperative hospital stay was 5.5 (4 to 8) days, and there were no immediate operative complications in any case. Patients were followed an average of 18.5 (13 to 24) months. A ureteral stricture developed in one patient and was resolved by ureteroureterostomy 3 months after the first operation. CONCLUSION: As an impacted ureteral stone is always associated with chronic ureteritis, firmness and adhesion of the periureteral tissue make the retroperitoneoscopic procedure difficult. In one case, a late complication of ureteral stricture may have been due to pre-existing severe chronic inflammation. Based on our limited experience, retroperitoneoscopic ureterolithotomy provides a practical alternative for the management of ureteral stones in selected patients. An expert clinician with experience in this procedure will provide the best results.

Humans↗
PubMed2000

Risk factors for renal allograft survival in patients receiving cyclosporine immunosuppression.

BACKGROUND AND PURPOSE: Although cyclosporine (CsA) has been widely used in renal transplantation for more than 10 years, no large series of renal transplant patients has been studied in southern Taiwan. The purpose of this retrospective cohort study was to investigate the risk factors for graft survival in renal transplant recipients. METHODS: From August 1987 to January 1998, 101 primary cadaveric renal transplantations were performed. The minimum follow-up period was 1 year. CsA and prednisolone were initially used as immunosuppressive agents in all patients. Use of lower doses of CsA to reduce CsA trough level (50-99 ng/mL) in hepatitis B surface antigen (HBsAg)-positive recipients was attempted at 6 months after transplantation. RESULTS: Graft actuarial survival rates at 1, 5, and 10 years posttransplantation were 89%, 75%, and 57%, respectively. Acute rejection and increased recipient age were found to be significant risk factors (p < 0.05) affecting graft survival, with hazard ratios of 5.20 and 1.74, respectively, by multivariate analysis using a Cox proportional hazards model. Hepatitis B and/or hepatitis C infection had no influence on graft survival. CONCLUSIONS: In this series of cadaveric renal allograft patients, the risk factors affecting allograft survival were acute rejection and recipient age.

Adolescent↗
PubMed1997

Unusual imaging presentations in renal transitional cell carcinoma.

PURPOSE: To report on unusual imaging presentations in renal transitional cell carcinoma (TCC). MATERIAL AND METHODS: Imaging studies of 140 cases of pathologically proven renal TCC were retrospectively studied with the focus on unusual presentations. RESULTS: Unusual imaging manifestations were found in 20 cases (14.3%). These findings were classified into 5 categories: perirenal abscesses or perirenal hematomas in 6 cases; parenchymal masses in 5; undue thickening of the hydronephrotic wall in 4; "tuberculoid" pyelograms in 3; and tumors with massive necrosis in 2. CONCLUSION: Deceptive imaging presentations may occur in renal TCC. Recognition of these presentations may help to prevent delay in diagnosis.

Abscess↗
PubMed1995

Vegetable consumption, serum retinol level, and risk of hepatocellular carcinoma.

A cohort of 8436 men in Taiwan was recruited with personal interview and blood sample collection between 1984 and 1986. During the 5-year follow-up period, 50 incident cases of hepatocellular carcinoma (HCC) were identified. Retinol levels were measured for 35 HCC patients whose serum samples were available and 140 matched controls randomly selected from cohort members without HCC. Lower vegetable intake was significantly associated with an increased risk of HCC after adjustment for other HCC risk factors (P = 0.006). The effect of low vegetable intake on HCC risk was limited to hepatitis B virus chronic carriers and cigarette smokers. As compared with subjects who had a weekly vegetable consumption frequency of six or more meals, the multivariate-adjusted relative risk of HCC for subjects who had a frequency of less than six meals was 4.7 (95% confidence interval, 2.0-11.1; P = 0.0004) among chronic hepatitis B virus carriers and 3.8 (95% confidence interval, 1.7-8.5; P = 0.001) among cigarette smokers. There was an inverse dose-response relationship between the prediagnostic serum retinol level and the development of HCC (trend test, P = 0.003). The odds ratio of HCC for men with a retinol level in the lowest tertile was 9.0 (95% confidence interval, 2.1-39.1) compared with those with a level in the highest tertile. The relation remained after multivariate adjustment for cigarette smoking, habitual alcohol drinking, and either the seropositivity of hepatitis B virus surface antigen and/or anti-hepatitis C virus antibody or the past history of liver diseases through conditional logistic regression analysis. The association was more striking for men 55 years or younger and for those who smoked 10 or more cigarettes/day. There was a significant synergistic effect of hepatitis B virus surface antigen carrier status and low serum retinol level on the development of HCC. These data suggest a potential role of retinol in the chemoprevention of HCC.

Adult↗
PubMed1992

Abscess of urachal remnant mimicking urinary bladder neoplasm.

Three cases of urachal abscess with extensive interstitial inflammation and fibrosis are reported. Clinically, all patients had a lower abdominal mass and CT scan and ultrasonic examination revealed a large tumour located anterior or superior to the bladder. They all underwent laparotomy and had either a partial cystectomy or an en bloc resection of the bladder and adjacent organs due to severe adhesions. Microscopic examination of the specimens revealed no evidence of carcinoma and only abscess formation with extensive chronic interstitial inflammation and fibrosis were seen. In one case, residual columnar epithelium suggestive of urachal origin was identified in the abscess cavity. Urachal abscess should be considered when dealing with lower abdominal masses.

Abscess↗