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J H Yoo

Publications and source records attributed to J H Yoo.

At least 19 recordsLinked to original sources
PubMed2004

Interaction of separated ferromagnetic domains in a hole-doped manganite achieved by a magnetic field.

We report the change in the magnetic microstructure with the application of a magnetic field to a hole-doped manganite La0.81Sr0.19MnO3 in the mixed-phase state, in which ferromagnetic and paramagnetic phases coexist. In situ observations by electron holography have revealed that the applied magnetic field generates a "channel" of the magnetic flux in the paramagnetic phase region, thereby connecting the separated ferromagnetic domains. The magnetic flux density of this channel is estimated at 0.33 T, which is comparable with that of the ferromagnetic domains. The connection of the separated ferromagnetic domains appears to promote the conduction in the mixed-phase state as predicted for many manganites exhibiting the magnetoresistance effect.

Journal Article↗
PubMed2003

Magnetization distribution in the mixed-phase state of hole-doped manganites.

The effect of 'colossal magnetoresistance' (CMR) in hole-doped manganites--an abnormal decrease of resistivity when a magnetic field is applied--has attracted significant interest from researchers in the past decade. But the underlying mechanism for the CMR phenomenon is not yet fully understood. It has become clear that a phase-separated state, where magnetic and non-magnetic phases coexist, is important, but the detailed magnetic microstructure of this mixed-phase state is so far unclear. Here we use electron microscopy to study the magnetic microstructure and development of ferromagnetic domains in the mixed-phase state of La(1-x)Sr(x)MnO3 (x = 0.54, 0.56). Our measurements show that, in the absence of a magnetic field, the magnetic flux is closed within ferromagnetic regions, indicating a negligible magnetic interaction between separated ferromagnetic domains. However, we also find that the domains start to combine with only very small changes in temperature. We propose that the delicate nature of the magnetic microstructure in the mixed-phase state of hole-doped manganites is responsible for the CMR effect, in which significant conduction paths form between the ferromagnetic domains upon application of a magnetic field.

Journal Article↗
PubMed2003

Computed tomographic findings of the fractured mandibular condyle after open reduction.

The purpose of this study was to evaluate the long-term radiological results obtained with open reduction and fixation of unilateral mandibular condyle fractures in 10 patients. CT images taken at the end of the follow-up period (average of 22 months, range 7 to 33 months), were traced and digitized, and the position and morphology of the fractured condylar process was statistically compared with those of the contralateral non-fractured condylar process in the coronal, transverse and sagittal planes. Little difference was observed in the position or morphology of the condylar process in the operated and non-fractured joints. This study shows that it is possible to anatomically reduce fractured condyles, and thereby to avoid postoperative disadvantageous joint changes.

Adult↗
PubMed2001

Determination of the native form of FadD, the Escherichia coli fatty acyl-CoA synthetase, and characterization of limited proteolysis by outer membrane protease OmpT.

Several studies have described FadD, the Escherichia coli fatty acyl-CoA synthetase [also known as fatty acid:CoA ligase (AMP-forming); EC 6.2.1.3], as a 42-50 kDa enzyme. Based on sequencing and expression data from the fadD gene, other reports have suggested that FadD is a 62 kDa protein and represents the sole fatty acyl-CoA synthetase in E. coli. We report that the 62 kDa FadD enzyme is a substrate for the outer membrane protease OmpT in vitro, producing a 43 kDa C-terminal fragment and a 19 kDa N-terminal fragment. Immunoblotting with a FadD antibody revealed that only the 62 kDa form of the enzyme is present in vivo, but we utilized the proteolytic sensitivity of FadD to investigate its structure. Photoaffinity labelling experiments revealed that both intact FadD and the 43 kDa fragment bound a long-chain fatty acid. Intact and cleaved FadD were also purified to determine the effect of cleavage on function. When using oleate as a substrate, cleaved FadD displayed 2-fold higher K(m) and V(max) values compared with intact FadD, but the catalytic efficiencies (k(cat)/K(m)) of the two forms were similar. This indicated that cleavage did not adversely affect enzyme activity. Proteolysis of FadD by OmpT was altered by the presence of oleate or ATP, both of which are ligands for the fatty acyl-CoA synthetase. This suggested that FadD undergoes ligand-induced conformational changes and implies that the region surrounding the cleavage site is mobile, a common characteristic of linker domains.

Acyl-CoA Dehydrogenase, Long-Chain↗
PubMed2001

Cold accumulation of SCOF-1 transcripts is associated with transcriptional activation and mRNA stability.

Cold acclimation enhances the transcription of several cold regulated (COR) genes. However, little is known about whether the elevation of the transcriptional level of the COR genes is due to transcriptional activation, or mRNA stability by a low temperature. Recently, we cloned a novel cold-inducible zinc finger protein gene from soybean, SCOF-1, which may function as a positive regulator of the COR gene expression . Here we report that the elevation of the SCOF-1 transcript level by cold stress is associated with both transcriptional activation and post-transcriptional mRNA stability under a low temperature. A nuclear run-on assay reveals that cold acclimation elevates the SCOF-1 transcript about three-fold compared to that of non-acclimated soybean nuclei. Furthermore, SCOF-1 transcripts increased substantially by a low temperature in transgenic tobacco plants that constitutively expressed SCOF-1 under the control of a constitutive cauliflower mosaic virus (CaMV) 35S promoter. When a transcription inhibitor, cordycepin, was treated with the deacclimating soybean cell, the decay level of the SCOF-1 transcripts was delayed significantly. This suggests that it may affect de novo protein synthesis, which degrades the SCOF-1 mRNA at room temperature. In addition, a secondary structure may be involved in the mRNA stability of SCOF-1 under a low temperature.

Acclimatization↗
PubMed2001

Dynamic sagittal imbalance of the spine in degenerative flat back: significance of pelvic tilt in surgical treatment.

STUDY DESIGN: A retrospective study of 26 patients with degenerative flat back treated with corrective osteotomy. OBJECTIVE: To analyze dynamic sagittal imbalance and to elucidate the cause of postoperative persistent stooping in degenerative flat back. SUMMARY OF BACKGROUND DATA: Sagittal spinal imbalance in degenerative flat back was more evident on walking, suggesting its dynamic nature. The most puzzling complication in its surgical treatment was postoperative persistent stooping. METHODS: This study analyzed 26 surgically treated patients with preoperative gait analysis. Patients were divided into two groups according to postoperative improvement in stooping: Group 1 with marked improvement in stooping and Group 2 with persistent stooping. Various radiographic and gait parameters were compared between the two groups. RESULTS: Comparison of radiographic parameters, representing the static status of the spine, did not indicate any clue to the mechanism for persistent stooping. However, comparison of gait parameters, representing the dynamic status of the spine, revealed meaningful differences between the two groups. Among various gait parameters compared, pelvic tilt seemed to be the most important clue. Patients in Group 1 showed posterior pelvic tilt, whereas those in Group 2 showed marked anterior pelvic tilt. CONCLUSION: Degenerative flat back could be classified into two types based on pelvic position during walking: one with posterior pelvic tilt and the other with marked anterior pelvic tilt. In the former type, corrective surgery improved the stooping. In the latter, corrective surgery was ineffective, resulting in postoperative persistent stooping.

Adult↗
PubMed2001

Existence of phase explosion during laser ablation and its effects on inductively coupled plasma-mass spectroscopy.

A sudden increase in crater depth was observed during high irradiance (> 10(10) W/cm2) laser ablation of silicon, and it is attributed to the phenomenon of phase explosion. The threshold irradiance for phase explosion showed a dependence on two laser parameters: laser beam spot size and wavelength. For a larger beam size and longer incident wavelength, a higher laser irradiance was required to generate phase explosion. The rapid increase of crater depth above the phase explosion threshold irradiance correlated with a significant increase in the ICPMS signal intensity. The ratio of crater volume to ICPMS intensity, which represents entrainment efficiency, remained the lowest at laser irradiances slightly above the phase explosion threshold. However, this ratio increased at irradiances well above the threshold (> 10(11) W/cm2). Chemical analysis using laser ablation at irradiance above 10(11) W/cm2 provides increased sensitivity via improved entrainment and transport efficiency and increased ablation rate.

Journal Article↗
PubMed2001

Molecular cloning of the orphanin FQ receptor gene and differential tissue expression of splice variants in rat.

Pharmacological and receptor-ligand binding studies of the cloned orphanin FQ (OFQ) receptor suggest that multiple forms of this receptor may exist. To further characterize the OFQ receptor (OFQR), we attempted to isolate the gene encoding this receptor in rat. The OFQR gene exceeds 10 kb in length and contains six exons ranging from 34 to 524 bp that are interrupted by five introns. The ATG translation initiation codon is located in exon 2, and the open reading frame consists of 1283 bp. Primer extension analysis of the gene revealed two major transcription initiation sites: one in the 5' flanking region and the other in intron 1. The rat OFQR gene appeared to be alternatively spliced to yield multiple mRNAs. Four splice variants deleted for exon 1 were expressed only in brain. In contrast, five isoforms containing exon 1 were expressed in various tissues, such as brain, testes, and gastrointestinal tract. These data suggest that unique regions in intron 1 and in the 5' flanking region of the OFQR gene contribute to the regulation of its expression in different tissues.

Alternative Splicing↗
PubMed2001

Elevated levels of plasma homocyst(e)ine and asymmetric dimethylarginine in elderly patients with stroke.

Cerebrovascular risk factors, including hypertension, smoking, diabetes mellitus, aging, dyslipidemia, and hyperhomocyst(e)inemia are linked to endothelial dysfunction. Endothelial-derived nitric oxide (NO) has inhibitory effects on key processes in atherothrombosis. Although asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, is associated with atherosclerotic disease, there has been no report on association of ADMA with ischemic stroke. Here we investigated the relation of plasma ADMA, stroke, and homocyst(e)inemia in the elderly. Plasma ADMA and homocyst(e)ine concentration was determined using high-performance liquid chromatography and fluorescence detection. Patients with ischemic stroke had significantly higher concentrations of plasma ADMA than controls (1.85+/-1.32 vs. 0.93+/-0.32 micromol/l, P=0.0001). After adjustment for risk factors, elevated ADMA levels, above 90th percentile of normal controls (> or =1.43 micromol/l) was associated with stroke (OR=6.05, 95% CI; 2.77-13.3, P=0.02). ADMA plasma levels were positively correlated to homocyst(e)ine levels (r=0.43, P=0.01). Multiple logistic regression analysis revealed that hyperhomocyst(e)inemia (plasma homocyst(e)ine concentration > or =15.0 micromol/l) was a significant predictor of elevated ADMA level. Altogether, findings indicate that elevated ADMA concentrations are at increased risk for ischemic stroke in the elderly, and may account for increased risk of stroke in patients with hyperhomocyst(e)inemia.

Aged↗
PubMed2001

Microsatellite instability in double primary cancers of the colorectum and stomach.

Little is known about genetic alterations of patients who present multiple primary cancers. We hypothesized that microsatellite instability (MSI) is one of the underlying genetic factors in the development of double primary cancers in colorectal cancer patients. We examined for MSI in 41 colorectal cancer patients who presented with extra-colonic primary cancers consisted of 17 gastric and 24 non-gastric cancers. Coincident MSI+ in tumors of two organs were observed in 3 (17.7%) of 17 patients with colon and stomach cancers and 0 of 24 patients with colon and non-gastric cancers (P =.03). In 17 patients with colon and stomach cancers, 6 (31.6%) of 19 colon cancers and 3 (17.7%) of 17 gastric cancers exhibited MSI+. Among four patients with metachronous colon cancers who were identified within the 41 double primary cancer patients, two patients were associated with the MSI+ phenotype. In summary, the prevalent coincidence of MSI suggests that genetic defect of mismatch repair deficiency may be responsible for a small subset of double primary cancers of the colorectum and stomach.

Aged↗
PubMed2001

Effect of pre-treatment on the surface and electrochemical properties of screen-printed carbon paste electrodes.

The effect of various electrochemical pre-treatment methods on the surface and electrochemical properties of screen-printed carbon paste electrodes (SPCE) prepared with three different commercial products was examined. It was observed that a positively charged redox couple, e.g., hexaammineruthenium(III), exhibited quasi-reversible behavior at the untreated SPCE. However, the cyclic voltammograms (CVs) of the SPCE prepared with general-purpose carbon inks did not exhibit clear redox peaks to other representative redox couples [e.g., hexacyanoferrate(III), hexachloroiridate(IV), dopamine, and hydroquinone] without activation. Electrochemical pre-treatment methods were sought in four different aqueous solutions, i.e., sulfuric acid, potassium chloride, sodium hydrogencarbonate, and sodium carbonate, applying various activation potentials. It was found that the pre-treatment procedure in saturated Na2CO3 solution at 1.2 V provides a mild and effective condition for activating the SPCE. By measuring the water contact angles at the SPCE surfaces and recording their SEM images, it was confirmed that the electrochemical pre-treatment effectively removes the organic binders from the surface carbon particles. A prolonged period of activation (> 5 min) or the use of high potentials (> 1.2 V) increased the capacitance of the electrode over 20 microF cm(-2). The pre-treated SPCE behaved like a random array microelectrode, exhibiting a sigmoidal-shaped CV at a slow scan rate. The short pre-anodization method in Na2CO3 solution was generally applicable to most SPCE prepared with general-purpose carbon inks.

Journal Article↗
PubMed2001

Clinical effects of pranlukast, an oral leukotriene receptor antagonist, in mild-to-moderate asthma: a 4 week randomized multicentre controlled trial.

OBJECTIVE: Leukotriene antagonists are increasingly used in asthma management. Pranlukast is a new, orally active, selective inhibitor of CysLt1 leukotriene receptor. The present clinical trial was performed to study the effect and safety of pranlukast in mild-to-moderate asthma. METHODOLOGY: A randomized, double-blind, placebo-controlled, parallel group study was performed in eight medical centres in Korea. Mild-to-moderate asthma patients who had been treated with beta2-agonists and/or inhaled corticosteroids were studied. The patients' symptoms were evaluated by asthma diary and twice-daily peak flow monitoring. RESULTS: Of the 206 patients enrolled, 197 were eligible for analysis. The pranlukast group (n = 98) showed statistically significant improvement in asthma symptoms, including asthma attack rate, daily living score, and morning and evening asthma scores. Pranlukast significantly reduced the consumption of beta2-agonist. Compared with the placebo group, forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1) were not significantly higher in the pranlukast group. Morning and evening peak expiratory flow (PEF) were significantly increased after pranlukast treatment at weeks 2 and 4 (380.8 +/- 10.1 L/min at baseline, 394.5 +/- 10.1 at week 2, 396.3 +/- 10.4 at week 4). There were no serious adverse reactions. CONCLUSION: Pranlukast, an oral leukotriene antagonist, was well tolerated and was effective for the management of mild-to-moderate asthma.

Adrenergic beta-Agonists↗
PubMed2001

Clinical evaluation of 3 types of plate osteosynthesis for fixation of condylar neck fractures.

PURPOSE: The goal of this study was to evaluate outcomes in patients who had condylar neck fractures treated with 3 different plating techniques. PATIENTS AND METHODS: A retrospective study was performed on 37 patients with 40 fractures of the condylar neck that were reduced and stabilized using an approach involving exposure of the facial nerve. Stabilization was achieved with a single miniplate (17 fractures), a minidynamic compression plate (13 fractures), or double miniplates (10 fractures). RESULTS: Plate fracture or screw loosening was exclusively observed in cases stabilized with either a single miniplate or a minidynamic compression plate. No cases of inadequate stability were observed when 2 miniplates were used. CONCLUSIONS: The 2-miniplate fixation technique provides functionally stable fixation for fractures of the condylar neck.

Adolescent↗
PubMed2001

MRI examination of the TMJ after surgical treatment of condylar fractures.

The position of discs in 20 adult patients whose unilateral condylar fractures were treated by open reduction was investigated by means of magnetic resonance imaging. In four (20%) of the 20 cases, the disc was anteriorly displaced in both the closed mouth and open mouth positions. Three of the four cases had a high condylar neck fracture with dislocation and one had a high condylar neck fracture with displacement. The results of this study showed that repositioning the dislocated condyle did not always lead to anatomical restoration of the joint structures.

Adult↗
PubMed2001

Effect of pentoxifylline on ischemic acute renal failure in rabbits.

Previous studies have demonstrated that levels of tumor necrosis factor-alpha (TNF-alpha) or its mRNA expression are increased in acute renal failure of various types including ischemia/reperfusion injury. This study was undertaken to determine whether pentoxifylline (PTX), an inhibitor of TNF-alpha production, provides a protective effect against ischemic acute renal failure in rabbits. Renal ischemia was induced by clamping bilateral renal arteries for 60 min. Animals were pretreated with PTX (30 mg/kg, i.v.) 10 min before release of clamp. At 24 h of reperfusion of blood after ischemia, changes in renal function, renal blood flow, and the expression of TNF-alpha mRNA were evaluated. Ischemia/reperfusion caused a marked reduction in GFR, which was accompanied by an increase of serum creatinine levels. Such changes were significantly attenuated by PTX pretreatment. PTX ameliorated the impairment of renal tubular function, but it had no effect on the reduction of renal blood flow induced by ischemia/reperfusion. The protective effect of PTX on functional changes was supported by morphological studies. The impairment of glucose and phosphate reabsorption in postischemic kidneys was associated with a depression in the expression of Na+-glucose and Na+-Pi transporters. The expression of TNF-alpha mRNA was increased after reperfusion, which was inhibited by PTX pretreatment. The PTX pretreatment in vitro prevented the release of lactate dehydrogenase induced by an oxidant t-butylhydroperoxide in rabbit renal cortical slices, but it did not produce any effect on the oxidant-induced lipid peroxidation, suggesting that PTX protection is not resulted from its antioxidant action. These results suggest that PTX may exert a protective effect against ischemic acute renal failure by inhibiting the production of TNF-alpha in rabbits.

Acute Kidney Injury↗