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Biomedical subjects

W T Lu

Publications and source records attributed to W T Lu.

At least 19 recordsLinked to original sources
PubMed2006

Duality between quantum and classical dynamics for integrable billiards.

We establish a duality between the quantum wave vector spectrum and the eigenmodes of the classical Liouvillian dynamics for integrable billiards. Signatures of the classical eigenmodes appear as peaks in the correlation function of the quantum wave vector spectrum. A semiclassical derivation and numerical calculations are presented in support of the results. These classical eigenmodes can be observed in physical experiments through the autocorrelation of the transmission coefficient of waves in quantum billiards. Exact classical trace formulas of the resolvent are derived for the rectangle, equilateral triangle, and circle billiards. We also establish a correspondence between the classical periodic orbit length spectrum and the quantum spectrum for integrable polygonal billiards.

Journal Article↗
PubMed2005

Soluble kagome Ising model in a magnetic field.

An Ising model on the kagome lattice with super-exchange interactions is solved exactly under the presence of a nonzero external magnetic field. The model generalizes the super-exchange model introduced by Fisher in 1960 and is analyzed in light of a free-fermion model. We deduce the critical condition and present detailed analyses of its thermodynamic and magnetic properties. The system is found to exhibit a second-order transition with logarithmic singularities at criticality.

Journal Article↗
PubMed2004

Negative refraction and left-handed electromagnetism in microwave photonic crystals.

We demonstrate the negative refraction of microwaves in a metallic photonic crystal prism. The spectral response of the photonic crystal prism, which manifests both positive and negative refraction, is in complete agreement with band-structure calculations and numerical simulations. The validity of Snell's law with a negative refractive index is confirmed experimentally and theoretically. The negative refraction observed corresponds to left-handed electromagnetism that arises due to the dispersion characteristics of waves in a periodic medium. This mechanism for negative refraction is different from that in metamaterials.

Journal Article↗
PubMed2003

Fractal Weyl laws for chaotic open systems.

We present a conjecture relating the density of quantum resonances for an open chaotic system to the fractal dimension of the associated classical repeller. Mathematical arguments justifying this conjecture are discussed. Numerical evidence based on computation of resonances of systems of n disks on a plane are presented supporting this conjecture. The result generalizes the Weyl law for the density of states of a closed system to chaotic open systems.

Journal Article↗
PubMed2001

Ising model on nonorientable surfaces: exact solution for the Möbius strip and the Klein bottle.

Closed-form expressions are obtained for the partition function of the Ising model on an MxN simple-quartic lattice embedded on a Möbius strip and a Klein bottle. The solutions all lead to the same bulk free energy, but for finite M and N the expressions are different depending on whether the strip width M is odd or even. Finite-size corrections at criticality are analyzed and compared with those under cylindrical and toroidal boundary conditions. Our results are consistent with the conformal field prediction of a central charge c=1/2, provided that the twisted Möbius boundary condition is regarded as a free or fixed boundary.

Journal Article↗
PubMed2001

Reduction in primary nonfunction of syngeneic islet transplants with nordihydroguaiaretic acid, a lipoxygenase inhibitor.

To study the effectiveness of a lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA), in the reduction of primary nonfunction, an insufficient number of syngeneic islets were transplanted underneath the renal capsule with NDGA administered daily for 4 weeks. After transplantation of the 150 islets, the decrement of blood glucose levels was significantly faster in the mice that had received NDGA than in the mice that had received no drug at all or dimethyl sulfoxide (DMSO) (p < 0.005, p < 0.05). The mean duration of temporary posttransplant hyperglycemia was 22.3 +/- 3.2 (n = 10), 35.9 +/- 2.3 (n = 14), and 33.7 +/- 4.1 (n = 6) days for the respective groups. The diabetic mice that received 300 islets had their blood glucose levels decrease faster than those that received 150 islets (19.7 +/- 1.6 vs. 35.9 +/- 2.3 days, n = 14. p < 0.0001). There was no significant difference in the blood glucose reducing effect between the mice that received 150 islets with NDGA and the mice that received 300 islets [22.3 +/- 3.2 (n = 10) vs. 19.7 +/- 1.6 (n = 14) days, p > 0.05]. The insulin content of the graft from the mice treated with 150 islets and NDGA (3.02 +/- 0.24 microg, n = 4) was higher than that from the mice that received 150 islets but no treatment (1.10 +/- 0.26 microg, n = 15, p < 0.005) or that had been treated with DMSO (1.21 +/- 0.30 microg, n = 4, p <0.05). The insulin content of the pancreas remnant had no significant differences among the three groups. The net glucose-stimulated insulin secretion was 0.82 +/- 0.14 vs. 0.20 +/- 0.10 microIU/islet x 60 min (n = 8, p < 0.005) and 0.59 +/- 0.08 vs. 0.04 +/- 0.02 microIU/islet x 60 min (n = 8, p < 0.0001) for islets cultured without NDGA vs. with NDGA at 1 and 2 weeks, respectively. However, the insulin content of the cultured islets was similar between the two groups for up to 2 weeks of incubation (at 1 week: 0.71 +/- 0.01 vs. 0.67 +/- 0.04 ng/islet, n = 8, p > 0.05; at 2 weeks: 0.71 +/- 0.02 vs. 0.80 +/- 0.07 ng/islet, n = 8, p > 0.05). Serum leukotriene B4 (LTB4) concentrations before and between the fifth and seventh days after transplantation were determined. For diabetic mice that received 150 islets, serum LTB4 levels were 25,835 +/- 3,335 and 27,631 +/- 3,136 pg/ml (n = 4, p > 0.05). For diabetic mice that received 150 islets and NDGA, the corresponding figures were 22,401 +/- 2,706 pg/ml and 27,530 +/- 2,190 pg/ml (n = 8, p > 0.05). The graft histology revealed viable islet cells and networks of close vascular structures around the islets and did not reveal microscopic differences among the samples of all four groups. In conclusion, our data revealed that daily administration of NDGA for 4 weeks enhanced isoislet engraftment and preserved three times more mass of the islet beta cells in the isografts. This result indicates that NDGA reduces primary nonfunction of islet syngeneic grafts in diabetic mice.

Animals↗
PubMed1999

Identification of familial hypercholesterolemia in Taiwan: report of eleven cases.

BACKGROUND: Familial hypercholesterolemia is associated with a very high risk of premature coronary heart disease. In order to identify cases of familial hypercholesterolemia in Taiwan, we screened the hyperlipidemic patients in our metabolic clinics. METHODS: Hyperlipidemic patients were screened in the metabolic outpatient department and the cases which fulfilled the clinical criteria of definitive or possible familial hypercholesterolemia were further analyzed. Their clinical characteristics, including age, gender, physical findings, past history of coronary heart disease or cerebrovascular accident (CVA), family history, and lipid profiles before and after medical treatment, were reviewed. RESULTS: Eight women and 3 men fulfilled the diagnostic criteria. The mean age at diagnosis was 51.1 +/- 11.9 years old. Tendon xanthomas were found in 5 patients with definitive familial hypercholesterolemia. Coronary heart disease was confirmed in one patient and old CVA was noted in another 2 patients. The mean total cholesterol level was 390.3 +/- 88.9 mg/dl and the mean low density lipoprotein-cholesterol (LDL-cholesterol) level was 309.6 +/- 89.9 mg/dl before treatment. After a mean treatment duration of 45.2 months, the mean total cholesterol level and LDL-cholesterol level were 326.8 +/- 87.8 mg/dl and 249.1 +/- 91.1 mg/dl, respectively. CONCLUSION: Clinically diagnosed familial hypercholesterolemia indeed exists in Taiwan. As compared to other reports, the mean age at diagnosis in our series was older and the majority of patients were women. Most patients were not vigorously treated and the family members were not thoroughly screened. Adequate treatment of patients with familial hypercholesterolemia in clinical practice and screening their family members are crucial in preventing new or recurrent coronary heart disease.

Adult↗
PubMed1998

Relative value of thallium-201 and iodine-131 scans in the detection of recurrence or distant metastasis of well differentiated thyroid carcinoma.

Radioactive iodine (131I) has been found to be more sensitive and more specific than thallium-201 for the detection of distant metastases and thyroid remnants in the neck in cases of well-differentiated thyroid carcinoma. 201Tl has been deemed particularly useful in localizing metastases or recurrence in patients with a negative 131I scan and abnormal levels of serum thyroglobulin (Tg). This study aimed to: (1) determine the value of 201Tl imaging in localizing metastases or recurrence in patients with well-differentiated thyroid carcinoma, and (2) evaluate the false-positive and false-negative results of 131I and 201Tl scintigraphy. Sixty-two thyroid remnant ablated patients who underwent simultaneous postoperative 201Tl and 131I scans and and serum Tg determinations were evaluated. Fifty patients had papillary thyroid carcinomas and 12 had follicular thyroid carcinomas. 201Tl imaging was performed before the 131I studies. Of the 62 patients who underwent 201Tl imaging studies, 24 were found to have positive results, with local recurrence or distant metastases. Patients with positive results in the 201Tl imaging studies tended to be older, were mor often male, had higher Tg levels and had a higher recurrence rate. Of these 24 patients, ten had negative diagnostic or therapeutic 131I scans. Concurrently, serum Tg levels were less than 5 ng/ml in five of these ten patients. Three patients were deemed false positive by 201Tl scans; one had a parotid tumour, one a periodontal abscess and one lung metastasis. Among the 38 patients with negative 201Tl scans, 11 had positive findings on 131I scans. Three had distant metastases: two with lung metastases and one with bone metastases. Patients with false-positive results on 131I scans included those with biliary tract stones, ovarian cysts, and breast secretion. Of the 27 patients with negative 201Tl and 131I scans, 15 had elevated serum Tg levels. Among these, local recurrence followed by lung metastases was manifested in a 49-year-old male with papillary thyroid carcinoma. In conclusion, both 131I and 201Tl scans are useful in the detection of recurrence or distant metastasis of well differentiated thyroid cancers. 201Tl scan could in particular be used in patients with a negative 131I scan in conjunction with an elevated Tg level.

Adult↗
PubMed1998

Anorectal function and endopelvic dissection in patients with repaired imperforate anus.

Fifty-eight patients with anorectal malformations were closely followed up for postoperative anorectal function. Constipation was noted shortly after anorectoplasty in 10 of 28 low anomalies (35.7%) treated with limited sagittal anorectoplasty (LSARP), in 18 of 25 high or intermediate anomalies (72.0%) treated with posterior sagittal anorectoplasty (PSARP), but in none of 5 high or intermediate anomalies treated with Rehbein's mucosa-stripping endorectal pull-through and anterior sagittal perineal anorectoplasty (R-ASAP). The constipation resolved mostly within 1-2 years after repair under conservative management, but persisted beyond 2 years after repair in 3/25 children with LSARP and 10/25 with PSARP. Anal soiling was noted in 1/23 (4.3%) LSARP and 6/22 (27.3%) PSARP patients, but normal anorectal function was attained in 20/23 LSARP (86.9%) and 11/12 PSARP patients (50.0%) by the time of toilet training. Manometric studies disclosed that the resting rectal pressure (RRP) was lower and the anorectal pressure gradient (ARPG) higher in the constipated than the non-constipated children, while the RRP was higher and the ARPG lower in the soiled than the non-soiled patients. The ARPG after R-ASPA was close to that of non-constipated and in between that of the constipated and soiled patients. The rectoanal sphincter inhibitory reflex was not related to defecation status or surgical procedures, but showed a tendency toward positive conversion with time or after exclusion of esctatic terminal bowel in the severely constipated. It is concluded that anorectal function in patients with repaired imperforate anus seems to be more affected by the extent of endopelvic dissection than by preservation of the terminal bowel or sphincter muscles.

Anal Canal↗
PubMed1998

Does surgery improve the survival of patients with advanced anaplastic thyroid carcinoma?

Anaplastic thyroid carcinoma is one of the most lethal neoplasms, with poor prognosis being reported by most authors. The benefits of surgery for most cases of advanced disease remain controversial. In this study we asked the following question: Does surgical intervention alter outcomes for patients with advanced anaplastic thyroid carcinoma? Forty-six patients with advanced anaplastic thyroid carcinoma were analyzed. There were 20 patients with advanced localized disease (group 1), 15 of whom received surgery. Of the other 26 patients with evidence of distant metastases (group 2), 13 received surgery. For group 1 patients, the mean survival was 12.8 months versus 8.6 months in the surgical and nonsurgical subgroups (p = 0.46). For group 2 patients, the mean survival was 3.5 months versus 2.8 months in the surgical and nonsurgical subgroups (p = 0.72). These data suggest that surgery does not improve survival for patients with advanced anaplastic thyroid carcinoma. In conclusion, the mean survival showed no significant differences between surgical and nonsurgical patients (p = 0.43). This study suggests that surgical resection does not improve the survival of patients with advanced anaplastic thyroid carcinoma.

Age Factors↗
PubMed1998

Factors affecting postoperative fecal soiling in Hirschsprung's disease.

We retrospectively assessed the factors that may contribute to fecal soiling after surgery for Hirschsprung's disease. Fifty-eight patients underwent surgery for Hirschsprung's disease and returned for follow up. The patients were divided into two groups based on the presence or absence of fecal soiling. The postoperative period, level of bowel pulled through, stool frequency, stool character, presence or absence of anorectal surgical complications, and manometric findings of the two groups were compared. Forty-three patients (40 boys, 3 girls, mean age 9.5 yr) had soiling and 15 (10 boys, 5 girls, mean age 10.2 yr) did not. Patients with soiling had significantly higher rates of anorectal surgical complications (60% vs 7%), abnormal stool character (75% vs 7%), stool frequency greater than three times per day (63% vs 20%), absence of rectoanal inhibitory reflex (33% vs 2%), and narrow anorectal pressure gradient (60% vs 13%) than those without. The results of manometric study suggested that a damaged internal sphincter or irritable neorectum might have contributed to fecal soiling. In conclusion, although anorectal surgical complications might result in both irritable neorectum and damaged internal sphincter, their effect on the neorectum (significantly increased rate of high resting rectal pressure) seemed to outweigh that on the internal sphincter. A competent anal sphincter and a less irritable neorectum after operation may therefore lower the likelihood of fecal soiling.

Adolescent↗
PubMed1997

Ketoacidosis with hyperglycemia in heavy drinkers: a report of 12 cases.

BACKGROUND: Heavy alcohol intake (> 45 g daily) might be a cause of diabetes. The short-term risks of heavy alcohol intake include ketoacidosis, glucose intolerance and pancreatitis. Alcoholic ketoacidosis (AKA) in combination with hyperglycemia mimics diabetic ketoacidosis (DKA). We described the characteristics of heavy drinkers with ketoacidosis and hyperglycemia but without a prior history of diabetes. METHODS: Twelve habitually heavy drinkers who had not been previously diagnosed as diabetes were identified by reviewing the records of diabetic patients admitted to Chang Gung Memorial Hospital from 1989 to 1992. All of them met DKA criteria. RESULTS: Elevated glycohemoglobulin (HbAlc) level is an indicator for the diagnosis of diabetes. Among these 12 patients, 10 had elevated levels of HbAlc and 2 had normal HbAlc levels. Of these 2 patients, 1 had an elevated level of HbAlc 6 months later; the other who was a female who after observation, had normal levels of HbAlc and glucose for the follow-up of two years. CONCLUSION: We found that most heavy drinkers with both ketoacidosis and hyperglycemia also had diabetes as indicated by high levels of HbAlc. The only female patient had normal HbAlc and was diagnosed as AKA rather than DKA.

Adult↗
PubMed1996

Mediastinal lymphangioma in an infant.

Lymphangioma confined exclusively to the mediastinum occurs rarely in patients under 2 years of age. A 17-month-old girl presented with recurrent respiratory symptoms and signs. Chest radiographs taken at 9 and 17 months of age showed a large mediastinal mass, which had increased in size during the interval. Sonography revealed the mass to be cystic and multiloculated. Magnetic resonance imaging demonstrated a heterogeneous mass lying in the anterior and superior mediastinum and enveloping the great vessels. The child underwent a left thoracotomy and the tumor was almost completely removed. The pathologic diagnosis was cavernous lymphangioma. The postoperative course was uneventful. Lymphangioma, though rare, should be considered in the differential list of mediastinal tumors and cysts in infants.

Female↗
PubMed1995

T-tube drainage for the treatment of high jejunal atresia.

Since 1976, the authors have used T-tube drainage for the treatment of diaphragmatic type, high jejunal atresia. Twelve cases were operated on. All cases survived the operation. On the fourteenth to thirtieth postoperative day, T-tubes were removed when the dilated proximal intestine returned to normal size.

Drainage↗