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E H Hwang

Publications and source records attributed to E H Hwang.

At least 19 recordsLinked to original sources
PubMed2005

Quasi-two-dimensional diluted magnetic semiconductor systems.

We develop a theory for two-dimensional diluted magnetic semiconductor systems (e.g., Ga(1-x)Mn(x)As layers) where the itinerant carriers mediating the ferromagnetic interaction between the impurity local moments, as well as the local moments themselves, are confined in a two-dimensional layer. The theory includes exact spatial disorder effects associated with the random local moment positions within a disordered RKKY lattice field theory description. We predict the ferromagnetic transition temperature (T(c)) as well as the nature of the spontaneous magnetization. The theory includes disorder and finite carrier mean-free path effects as well as the important correction arising from the finite temperature RKKY interaction, finding a strong density dependence of T(c) in contrast to the simple virtual crystal approximation.

Journal Article↗
PubMed2005

Temperature dependent weak field Hall resistance in two-dimensional carrier systems.

Using the Drude-Boltzmann semiclassical transport theory, we calculate the weak-field Hall resistance of a two-dimensional system at low densities and temperatures, assuming carrier scattering by screened random charged impurity centers. The temperature-dependent 2D Hall coefficient shows striking nonmonotonicity in strongly screened systems, and, in particular, we qualitatively explain the recent puzzling experimental observation of a decreasing Hall resistance with increasing temperature in a dilute 2D hole system. We predict that the impurity scattering limited Hall coefficient will eventually increase with temperature at higher temperatures.

Journal Article↗
PubMed2005

Two-dimensional metal-insulator transition as a percolation transition in a high-mobility electron system.

By carefully analyzing the low temperature density dependence of 2D conductivity in undoped high-mobility n-GaAs heterostructures, we conclude that the 2D metal-insulator transition in this 2D electron system is a density inhomogeneity driven percolation transition due to the breakdown of screening in the random charged impurity disorder background. In particular, our measured conductivity exponent of approximately 1.4 approaches the 2D percolation exponent value of 4/3 at low temperatures and our experimental data are inconsistent with there being a zero-temperature quantum critical point in our system.

Journal Article↗
PubMed2004

Disordered RKKY lattice mean field theory for ferromagnetism in diluted magnetic semiconductors.

We develop a lattice mean field theory for ferromagnetic ordering in diluted magnetic semiconductors by taking into account the spatial fluctuations associated with random disorder in the magnetic impurity locations and the finite mean free path associated with low carrier mobilities. Assuming a carrier-mediated indirect RKKY exchange interaction among the magnetic impurities, we find substantial deviation from the extensively used continuum Zener model Weiss mean field predictions. Our theory allows accurate analytic predictions for Tc and provides simple explanations for a number of observed anomalies, including the non-Brillouin function magnetization curves, the suppressed low-temperature magnetization saturation, and the dependence of Tc on conductivity.

Journal Article↗
PubMed2003

Frictional drag in dilute bilayer 2D hole systems.

We develop a theory for frictional drag between two 2D hole layers in a dilute bilayer GaAs hole system, including effects of hole-hole and hole-phonon interactions. Our calculations suggest significant enhancement of hole drag transresistivity over the corresponding electron drag results. This enhancement originates from the exchange induced renormalization of the single-layer compressibility and the strong dependence of single-layer conductivity on density. We also address the effect of hole-phonon interaction on the drag temperature dependence. Our calculated results are in reasonable quantitative agreement with recent experimental observations.

Journal Article↗
PubMed2003

Resistivity of dilute 2D electrons in an undoped GaAs heterostructure.

We report resistivity measurements from 0.03 to 10 K in a dilute high mobility 2D electron system. Using an undoped GaAs/AlGaAs heterojunction in a gated field-effect transistor geometry, a wide range of densities, 0.16 x 10(10) to 7.5 x 10(10) cm(-2), are explored. For high densities, the results are quantitatively shown to be due to scattering by acoustic phonons and impurities. In an intermediate range of densities, a peak in the resistivity is observed for temperatures below 1 K. This nonmonotonic resistivity can be understood by considering the known scattering mechanisms of phonons, bulk, and interface ionized impurities. Still lower densities appear insulating to the lowest temperature measured.

Journal Article↗
PubMed2002

Inflammatory orbital pseudotumor with infratemporal fossa extension mimicking temporomandibular joint dysfunction.

Inflammatory orbital pseudotumor is a benign space-occupying lesion of unknown origin that involves all or part of the fatty tissue within the orbit. Occasionally the disease may extend into the middle cranial, the pterygopalatine, and the infratemporal fossa through the various foramina of the orbit, although extension into the infratemporal fossa is very rare. We present a case which extends into the infratemporal fossa through the inferior orbital fissure, resulting in presenting symptoms mimicking temporomandibular joint dysfunction.

Adult↗
PubMed2001

Multiple cemento-ossifying fibroma: report of an 18-year follow-up.

Multiple cemento-ossifying fibroma is a very rare jaw lesion. A unique case is reported involving a 43-year-old Korean woman with rapidly growing, multiple cemento-ossifying fibromas in all four quadrants over an 18-year period which resulted in severe facial deformity and orbital compression.

Adult↗
PubMed2001

Fistula-in-ano in infants: is nonoperative management effective?

PURPOSE: Recently, a number of studies have reported positive results from the nonoperative management of fistula-in-ano in infancy, although it has not been of use in all patients. The purpose of this study was to discern the effective treatment methods of fistula-in-ano in infants. METHODS: A retrospective review was done of 310 children who required operative management for fistula-in-ano or perianal abscess between January 1991 and July 2000. Eighteen patients displayed an onset of symptoms at less than 1 year of age and a duration of symptoms longer than 12 months. The authors analyzed these patients' medical records. RESULTS: All patients were boys. The mean duration of the symptoms was 26.6 +/- 27.5 months. Fourteen patients had shown an onset of symptoms at less than 6 months of age. The longest duration was 10 years. The patients showed conservative periods of over 12 months because their parents did not want them to undergo surgery. The disease in these patients followed 2 patterns. One (6 patients) was an onset of symptoms followed by a silent fistula-in-ano state. The other (12 patients) was an onset of symptoms followed by an intermittent relapse of inflammation. All patients underwent fistulotomy, and none of them had recurrent fistula during the follow-up period. CONCLUSIONS: Although the advantages of a nonoperative management of fistula-in-ano in infants include the avoidance of general anesthesia and surgical intervention, the lesions cannot be cured by a period of conservation. Surgical management is more effective in respect to the time factor.

Child↗
PubMed2001

Biliary atresia associated with meconium peritonitis caused by perforation of small bowel atresia.

BACKGROUND/PURPOSE: This report describes our experiences with 5 cases of biliary atresia associated with meconium peritonitis caused by perforation of small bowel atresia. METHODS: A review of medical records was undertaken in an effort to recognize cases of biliary atresia associated with meconium peritonitis. RESULTS: Five patients of 171 with biliary atresia (2.9%) were detected to have meconium peritonitis caused by perforation of small bowel atresia. The biliary atresia was not suspected during the initial operation for meconium peritonitis. Total parenteral nutrition (TPN) made it difficult to make an early differential diagnosis of biliary atresia because of the presence of TPN-associated cholestatic jaundice, and the Roux-en-Y limb used for hepatic portoenterostomy could not be made long enough to prevent cholangitis caused by preexisting short bowel. The main complications were severe, intractable cholangitis, short bowel syndrome with malnutrition; TPN-associated liver injury; and wound problems. Two patients died of ascending cholangitis, 1 patient of liver failure that was exacerbated by TPN-associated liver injury, and 1 patient is awaiting a liver transplant. Only 1 patient is in good health, being anicteric and showing normal growth and development. CONCLUSIONS: Biliary atresia is evidently closely associated with meconium peritonitis caused by perforation of small bowel atresia. The management of these patients is more difficult than that of patients with the usual form of biliary atresia, because of the necessity for a long period of TPN and the combined short bowel syndrome. The ideal management of these conditions has yet to be determined.

Biliary Atresia↗
PubMed2001

The development of fetal surgery.

The history of fetal surgery features an absolute dependency upon the possibility of diagnosis before birth. Powerful new imaging methods, the techniques of sampling amniotic fluid and fetal tissue, and modern molecular genetics for the prenatal diagnosis of various congenital diseases have removed the veil of secrecy from the fetus. Even though most prenatally detected congenital malformations can be managed after maternal transport, a few simple anatomic defects require fetal surgery, albeit with predictably poor results. The understanding of intrauterine physiology and pathophysiology in several congenital malformations has been worked out in animal model study, and the natural history of congenital defects revealed by prenatal observations on human fetuses. Selection criteria for intrauterine intervention have been developed. Over the last two decades, surgical techniques for open and endoscopic fetal surgery have been defined and anesthesia and tocolysis for fetal surgery improved. As we enter the 21st century, this field of surgery will surely expand.

Animals↗
PubMed2000

Peripheral sympathetic dysfunction in patients with Parkinson's disease without autonomic failure is heart selective and disease specific. taki@med.kanazawa-u.ac.jp.

UNLABELLED: The study was undertaken to investigate by means of iodine-123-labelled metaiodobenzylguanidine (MIBG) scintigraphy the peripheral sympathetic function in patients with Parkinson's disease (PD) without autonomic failure and in patients with related neurodegenerative diseases with parkinsonism. Seventy patients (33 men and 37 women, mean age 63+/-9.7 years) with parkinsonism and ten control subjects underwent MIBG scintigraphy. Of these 70 patients, 41 were diagnosed as having idiopathic PD, 9 multiple system atrophy (MSA), 6 progressive supranuclear palsy (PSP) and 2 corticobasal degeneration (CBD); the remaining 12 were diagnosed as having neurodegenerative disease with parkinsonism (P-nism) that did not meet the diagnostic criteria of any specific disease. Cardiac planar and tomographic imaging studies and subsequent whole-body imaging were performed 20 min and 3 h after the injection of 111 MBq MIBG. The early MIBG heart to mediastinum (H/M) ratio in PD (1.61+/-0.29) was significantly lower than that in the control group (2.24+/-0.14, P<0.01), P-nism (2.15+/-0.31, P<0.01), MSA (2.08+/-0.31, P<0.05) and PSP (2.30+/-0.24, P<0.01). The delayed H/M ratio in PD (1.47+/-0.34) was also significantly lower than that in the control group (2.37+/-0.14, P<0.01), P-nism (2.13+/-0.38, P<0.01), PSP (2.36+/-0.36, P<0.01) and MSA (2.17+/-0.36, P<0.01). In patients with PD, early and delayed H/M ratios were significantly decreased in disease stages I, II and III (established using the Hoehn and Yahr criteria) as compared with control subjects, and there were no significant differences among the stages. Only PD showed a significantly higher washout rate (WR) than that in the control subjects (27%+/-8.0% vs. 11%+/-4.2%, P<0.01). Early and delayed uptake ratios of the lung, parotid gland, thyroid gland, liver and femoral muscles in each of the patient groups were not significantly different from those in control subjects. Only the early and delayed uptake ratios of the lower leg muscles in MSA were significantly lower than those in the control group (P<0.05). IN CONCLUSION: In patients with PD without autonomic failure, only cardiac MIBG uptake was severely reduced in the earliest phase of the disease (stage I). Parkinsonian syndromes other than PD did not demonstrate significant reduction in MIBG uptake in any organs except for the lower legs in MSA. In patients with PD without autonomic failure, reduction in MIBG uptake occurs selectively in the heart; this is considered to be a specific finding for PD and useful for the differential diagnosis of the parkinsonian syndromes.

3-Iodobenzylguanidine↗
PubMed2000

Tailgut cyst in a neonate.

Tailgut cyst is a rare lesion of developmental origin located in the retrorectal space, which usually presents as a multilocular cystic mass. It is usually found in adults, and neonatal cases are extremely rare. The authors report a tailgut cyst in a neonate that was found by prenatal ultrasonogram, which was like a teratoma in gross appearance.

Cysts↗
PubMed2000

Biliary atresia in neonates and infants: triangular area of high signal intensity in the porta hepatis at T2-weighted MR cholangiography with US and histopathologic correlation.

PURPOSE: To correlate a triangular area of high signal intensity in the porta hepatis on T2-weighted magnetic resonance (MR) cholangiograms of biliary atresia with ultrasonographic (US) and histopathologic findings in a portal mass observed during a Kasai procedure. MATERIALS AND METHODS: Twenty-one consecutive neonates and infants (age range, 13-88 days; mean age, 59 days) with cholestasis underwent US and single-shot MR cholangiography. In 12 patients with biliary atresia diagnosed at histopathologic examination, MR cholangiographic findings in the porta hepatis were correlated with US and histopathologic findings in the portal mass. RESULTS: At US, eight of the 12 patients had round, linear, or tubular hypoechoic portions within a triangular cord; MR cholangiography revealed a triangular area of high signal intensity confined to the porta hepatis. Histopathologic examination of the portal mass revealed a cystic or cleftlike lesion surrounded by loose myxoid mesenchyme and platelike fetal bile ducts. Neither the large cystic lesion without ductal epithelium nor the small cleftlike lesion with scanty epithelium demonstrated bile staining. Similar areas of high signal intensity were not seen on T2-weighted images in the remaining patients (four with biliary atresia and nine with neonatal hepatitis). CONCLUSION: In biliary atresia, T2-weighted single-shot MR cholangiography can show a triangular area of high signal intensity in the porta hepatis that may represent cystic dilatation of the fetal bile duct.

Bile↗
PubMed1999

Simple scintigraphic parameters with Tc-99m galactosyl human serum albumin for clinical staging of chronic hepatocellular dysfunction.

Technetium-99m labeled diethylenetriaminepentaacetic acid (DTPA)-galactosyl human serum albumin (GSA) has been used for hepatocellular functional evaluation. This study proposed new and simple parameters to overcome the limitations of conventional parameters, and they were applied to the clinical staging of chronic liver dysfunction. The study group consisted of 93 patients including 81 with liver dysfunction and 12 control patients. In addition to the two conventional parameters, namely, receptor index (LHL15 = liver count divided by the sum of liver and heart counts at 15 minutes) and clearance index (HH15 = heart count at 15 minutes divided by the heart count at 3 minutes), 6 new parameters for Tc-99m GSA uptake and clearance were generated. The conventional receptor index of LHL15 showed a large variation depending on the size of region of interest (ROI) over the heart. The LHL15 normalized by the ROI size (nLHL15) showed more stable data and a better separation of mild liver dysfunction. A hyperbolic relationship between the LHL15 and HH 15 changed to a linear relationship by using the nLHL15 index. The combination of the liver to heart average count ratio at 15 minutes (LH 15) and T-half (minute) of the heart count also could differentiate each stage well. In conclusion, the use of the ROI-area normalized nLHL is recommended instead of the conventional LHL15. The indices of LH15 and T-half could be alternatively used as practical parameters for clinical staging in liver function.

Adult↗
PubMed1999

Multiple intestinal ulcerations and perforations secondary to methicillin-resistant Staphylococcus aureus enteritis in infants.

PURPOSE: The aim of this study was to define a distinctive clinical entity of multiple intestinal ulcerations and perforations in infants. METHODS: Two infants underwent abdominal exploration for surgical abdomen and were noted to have multiple intestinal ulcerations and perforations. A peculiar and unique surgical finding, numerous transverse linear ulcerations scattered along the entire small intestine, prompted us to search for similar instances. Five similar cases were additionally identified by members of the Korean Association of Pediatric Surgeons. The clinical courses, the surgical findings, and the results of bacterial cultures were reviewed. As well, the tissues of resected intestines were examined histopathologically. RESULTS: The characteristics of this entity are as follows. (1) It usually occurs in infants who have been treated with broad-spectrum antibiotics. (2) Despite broad-spectrum antibiotic treatment, diarrhea and abdominal distension developed progressively and deteriorated. (3) Histological evaluation showed mucosal ulcers with neutrophil infiltration, submucosal microabscesses, and colonies of Gram-positive cocci. (4) Methicillin-resistant Staphylococcus aureus (MRSA) was the predominant organism cultured from the body fluid. (5) Only two cases, the completely resected one and the one immediately treated postoperatively with vancomycin, survived. CONCLUSIONS: This entity is caused by multiple intestinal ulcerations and perforations secondary to MRSA enteritis in infants. It has a high mortality rate because of its difficult diagnosis. However, early recognition of this entity can lead to successful treatment.

Anti-Bacterial Agents↗