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Biomedical subjects

I Lee

Publications and source records attributed to I Lee.

At least 19 recordsLinked to original sources
PubMed2006

Characterization of a single molecular QCA cell by Q-control enhanced amplitude modulation atomic force microscopy.

Major technical challenges for reduction of device sizes for computation and memory are the interconnection and power dissipation problems. Molecular quantum-dot cellular automata (QCA) have been proposed as solutions to this problem. Silicon phthalocyanine (SiPc) is a possible candidate for a molecular QCA element. Therefore, it is important to develop an in situ observation technique to visualize individual SiPc molecules. We report here the first image of a single SiPc dimer in air by using quality factor control (Q-control) enhanced amplitude modulation atomic force microscopy (AFM) and an investigation of the interaction forces between the tip and SiPc dimer. The AFM was operated at 0% relative humidity in an ultrapure nitrogen environment either with or without Q-control. Theoretical simulations using the point-mass description of the AFM, demonstrated that Q-enhancement reduced the force exerted from the tip to the sample surface. Our results, consistent with theory, demonstrated that the image force was reduced and a greater height and a larger size were measured. The advantages of this method can be extended to the AFM observation of other "soft" structures, and these results can be useful for a wider community.

Computers, Molecular↗
PubMed2005

Quantitative postural load assessment for whole body manual tasks based on perceived discomfort.

Many Korean workers are exposed to repetitive manual tasks or prolonged poor working postures that are closely related to back pain or symptoms of musculoskeletal disorders. Workers engage in tasks that require not only handling of heavy materials, but also assuming prolonged or repetitive non-neutral work postures. Poor work postures that have been frequently observed in the workplaces of shipbuilding shops, manufacturing plants, automobile assembly lines and farms often require prolonged squatting, repetitive arm raising and wrist flexion and simultaneous trunk flexion and lateral bending. In most manufacturing industries, workers have to assume improper work postures repetitively, several hundreds of times per day depending on daily production rate. A series of psychophysical laboratory experiments were conducted to evaluate the postural load at various joints. A postural load assessment system was then developed based on a macro-postural classification scheme. The classification scheme was constructed based on perceived discomfort for various joint motions as well as previous research outcomes. On the basis of the perceived discomfort, postural stress levels for the postures at individual joints were also defined by a ratio scale to the standing neutral posture. Laboratory experiments simulating automobile assembly tasks were carried out to investigate the relationship between body-joint and whole-body discomfort. Results showed a linear relationship between the two types of discomfort, with the shoulder and low back postures being the dominant factor in determining the whole body postural stresses. The proposed method was implemented into a computer software program in order to automate the procedure of analysing postural load and to enhance usability and practical applicability.

Humans↗
PubMed2005

Distribution of new methylene blue injected into the caudal epidural space in cattle.

To investigate the distribution of solutions injected into the first intercoccygeal epidural space, 24 adult, standing cattle were randomly assigned to 5-, 10- and 20-mL groups and injected with 0.12% new methylene blue (NMB) in 0.9% saline. Ten heifers received 1 mL NMB solution/100 kg of body weight. There was a significant correlation between the injected volume and the number of cranially stained spinal segments in three adult cattle groups (correlation coefficient R2=0.46; P<0.0001). In three cattle, NMB solution did not distribute more than one spinal segment cranially from the injection site due either to fibrosis of the epidural tissue or to inadvertent intravenous administration into the epidural vein. The study showed that the larger the volume of solution injected, the greater the spread with increased individual variation. The results could form the basis for determining the volume of injection required and for evaluating the pharmacokinetics of anaesthetics used in caudal epidural anaesthesia.

Anesthesia, Epidural↗
PubMed2004

Deformability of poly(amidoamine) dendrimers.

Experimental data indicates that poly(amidoamine) (PAMAM) dendrimers flatten when in contact with a substrate, i.e. they are no longer spherical, but resemble flat disks. In order to better understand the deformation behavior of these branched polymers, a series of atomistic molecular dynamics simulations is performed. The resulting flattened dendrimer conformations are compared to atomic force microscopy (AFM) images of individual dendrimers at air/mica and water/mica interfaces. The ability of the polymers to deform is investigated as a function of dendrimer generation (2-5) and the required energies are calculated. Our modeling results show good agreement with the experimental AFM images, namely that dendrimers are highly flexible and capable of forming multiple interaction sites between most of their branch ends and the substrate. The deformation energy scales with dendrimer generation and does not indicate an increase in stiffness between generations 2 and 5 due to steric effects.

Biocompatible Materials↗
PubMed2003

Mesenchymal tumours of the thorax: CT findings and pathological features.

Mesenchymal tumours of the thorax are uncommon and may originate from the muscle, bone, cartilage, vessel, nerves, fat and fibrous tissue. These tumours occur at different sites including the lung, pleura, mediastinum or chest wall. Mesenchymal tumours tend to show protean and non-specific imaging characteristics. However, in some instances, the imaging characteristics of the tumour may allow a specific diagnosis to be made, such as with lipoid or vascular tumours.

Adolescent↗
PubMed2003

Antagonistic effects of intravenous or epidural atipamezole on xylazine-induced dorsolumbar epidural analgesia in cattle.

This study was performed to clarify the antagonistic actions of intravenous or epidural atipamezole on the sedative and analgesic effects of xylazine administered between the epidural fat and dura mater through the first interlumbar space in cattle. Cattle received 5 mL of a solution containing 0.05 mg x kg(-1) xylazine in 0.9% saline. Thirty minutes later, 5 mL of 0.9% saline was administered through the same needle (treatment 1) (XSE). In treatments 2 (XAE) and 3 (XAV), 5 mL of a solution containing 0.025 mg x kg(-1) atipamezole in 0.9% saline was administered epidurally or intravenously, respectively. Sedation and analgesia were similar in all three treatment groups and could be reversed by atipamezole given by either route. In the XAV treatment, the flank area relapsed into analgesia 25+/-5.8 min following reversal of the analgesic effect, and was maintained for 112.5+/-63.8 min. The present study confirmed that the sedative and analgesic effects of xylazine are completely reversed by atipamezole and can be influenced by the epidural fat in cattle. Furthermore, it seems probable that analgesia following epidural administration of xylazine is mediated by alpha(2)-adrenergic receptors, not by a local anaesthetic effect.

Adipose Tissue↗
PubMed2003

The relationship between mediastinal lymph node attenuation with parenchymal lung parameters in silicosis.

OBJECTIVE: Attenuation changes on computed tomography (CT) in mediastinal lymph nodes (LN) may be related to lung alterations and functional impairment in silicosis. DESIGN: CT and clinical data of 41 (64.2 +/- 8.3 years) males with silicosis were retrieved. Attenuation type (calcified, hyperdense, normodense) and calcification pattern (central, eccentric, dense, eggshell, speckled) of mediastinal LN were evaluated; LN attenuation of uncalcified LNs quantified on CT in six LN stations. Nodular profusion (CT-NP) and progressive massive fibrosis (CT-PMF) were graded. Relationships between LN, CT, lung function and clinical parameters were determined. RESULTS: LN sites were paratracheal (n = 39), subcarinal (n = 39), tracheobronchial (n = 37), aortopulmonary (n = 37), hilar (n = 27), and peri-oesophageal (n = 21). LNs were calcified, hyperdense and normodense in 107, 85 and 54 LN stations, respectively. Uniformly calcified LN was most common, followed by speckled calcification. Central, eccentric and eggshell calcification was rare. CT-NP scores > or = 16 were associated with higher LN attenuation and number of calcified LN stations than CT-NP scores < 16. PMF had no influence over LN morphology or calcification pattern. LN attenuation correlated with CT-PMF (r = 0.36, P = 0.01), CT-NP (r = 0.54, P < 0.001) and DLCO/VA (r = -0.33, P = 0.02). CONCLUSION: Uniformly calcified and hyperdense LNs are common in silicosis, and eggshell LN calcification is rare. There are associations between LN attenuation and lung function impairment, and CT grades of nodular profusion and PMF.

Aged↗
PubMed2002

Perceived occupational stress and related factors in public health nurses.

The purposes of this study were to explore perceived occupational stress and related factors in public health nurses (PHNs). A convenient sampling method was used to recruit the subjects. Seven out of 12 district health centers in Taipei City and all 11 district health centers in Kaohsiung City agreed to participate in this study. Of the 171 PHNs invited to participate, 167 (97.7%) completed all mailing questionnaires. Findings showed that (1) the major sources of occupational stress in PHNs were personal responsibility and workloads, and (2) PHNs with younger age, shorter length of current working experience, longer past clinical experience, higher level of education, and less pre-job or on-job continuous education perceived more occupational stress. The findings indicate that it is necessary to develop stress-alleviating programs to reduce occupational stress in PHNs. Designing a systematic in-service training program to enhance working competency and performance of PHNs is also suggested.

Adult↗
PubMed2002

Molecular views and measurements of hemostatic processes using atomic force microscopy.

Hemostasis and thrombosis are highly complex and coordinated interfacial responses to vascular injury. In recent years, atomic force microscopy (AFM) has proven to be a very useful approach for studying hemostatic processes under near physiologic conditions. In this report, we review recent progress in the use of AFM for studying hemostatic processes, including molecular level visualization of plasma proteins, protein aggregation and multimer assembly, and structural and morphological details of vascular cells under aqueous conditions. AFM offers opportunities for visualizing surface-dependent molecular and cellular interactions in three dimensions on a nanoscale and for sensitive, picoNewton level, measurements of intermolecular forces. AFM has been used to obtain molecular and sub-molecular, resolution of many biological molecules and assemblies, including coagulation proteins and cell surfaces. Surface-dependent molecular processes including protein adsorption, conformational changes, and subsequent interactions with cellular components have been described. This review outlines the basic principles and utility of AFM for imaging and force measurements, and offers objective perspectives on both the advantages and disadvantages. We focus primarily on molecular level events related to hemostasis and thrombosis, particularly coagulation proteins, and blood platelets, but also explore the use of AFM in force measurements and surface property mapping.

Adsorption↗
PubMed2002

Disturbance detection and isolation in the activated sludge process.

This paper proposes a new fault detection and isolation (FDI) method. This method monitors the distribution of process data and detects changes in this distribution, which reflect changes in the corresponding operating condition. A modified dissimilarity index and a FDI technique are defined to quantitatively evaluate the difference between data sets. This technique considers the importance of each transformed variable in the multivariate system. The FDI technique is applied to a benchmark simulation and to data from a real wastewater treatment plant. Simulation results show that it immediately detects disturbances and automatically distinguishes between serious and minor anomalies for various types of fault. The method not only detects the disturbances, but also isolates the scale of the disturbance, facilitating the interpretation of the disturbance source. The proposed monitoring technique is found to be appropriate for analyzing the biological wastewater treatment process, which is characterized by a variety of fault and disturbance sources and non-stationary characteristics.

Benchmarking↗
PubMed2001

Structure-reactivity relationships in the pyridinolysis of N-methyl-N-arylcarbamoyl chlorides in dimethyl sulfoxide.

Nucleophilic substitution reactions of N-methyl-N-arylcarbamoyl chlorides (YC(6)H(4)N(CH(3))COCl) with pyridines (XC(5)H(4)N) have been investigated in dimethyl sulfoxide at 45.0 degrees C. A striking trend in the selectivity parameters is that they are constant within experimental errors, rho(X) = -2.25 +/- 0.03, beta(X) = 0.42 +/- 0.01, and rho(Y) = 1.10 +/- 0.06, with changing reactivities of the electrophiles (deltasigma(Y)) and nucleophiles (deltasigma(X)), respectively, and this leads to a vanishingly small cross-interaction constant, rho(XY) approximately equals beta(XY) approximately equals 0. The rate data can be expressed in the Ritchie N(+) type equation. Based on this and other results, the mechanism of nucleophile (pyridine) addition to the resonance- stabilized carbocation is proposed. It has been shown from the definition of beta(XY) (and rho(XY)) together with the Marcus equation that the high intrinsic barrier, DeltaG(0), in the intrinsic-barrier controlled reaction series is a prerequisite for such reactions in which the cross-interaction vanishes and the N(+) relationship holds.

Journal Article↗
PubMed2001

Importance of the conserved CA dinucleotide at Mu termini.

The dinucleotide CA found at the termini of transposable phage Mu also occurs at the termini of a large class of transposable elements, including HIV, all retroviruses and many retrotransposons. In order to understand the importance of this sequence conservation, the activity of all 16 dinucleotide permutations of the termini was first examined using a sensitive plasmid-based in vivo transposition assay. The reactivity of these substrates varied over several orders of magnitude in vivo, with substitutions at the A position being more severely impaired than those at the C position. The same general hierarchy of reactivity was observed in vitro using mutant oligonucleotide substrates. These experiments revealed that CA was not important for the chemistry of strand transfer, and that the block in the activity of the mutant substrates was at the stage of assembly of a stable transpososome. Given that DNA at the Mu-host junctions is melted/distorted concomitantly with transpososome assembly, we consider the hypothesis that the CA dinucleotide has been selected at transposon termini primarily for its significant conformational mobility.

Bacteriophage mu↗
PubMed2001

Redox cycling by motexafin gadolinium enhances cellular response to ionizing radiation by forming reactive oxygen species.

PURPOSE: To examine the mechanism of radiation enhancement by motexafin gadolinium (Gd-Tex) in vitro. METHODS AND MATERIALS: Oxidation of ascorbate and NADPH by Gd-Tex was evaluated in a neutral buffer. Growth inhibition of human uterine cancer cell line MES-SA was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) dye. Clonogenic assays were used to measure radiation response in MES-SA, A549 human lung carcinoma, E89, a CHO cell line variant deficient in glucose-6-phosphate dehydrogenase activity, and murine lymphoma cell lines LYAR and LYAS. RESULTS: Gd-Tex catalyzed the oxidation of NADPH and ascorbate under aerobic conditions, forming hydrogen peroxide. Decreased viability was observed in MES-SA cells incubated with Gd-Tex in media containing NADPH or ascorbate. Gd-Tex and ascorbate increased fluorescence in dichlorofluorescin acetate-treated cultures. Synergistic effects on the aerobic radiation response in MES-SA and A549 were seen using Gd-Tex in combination with L-buthionine-(S,R)-sulfoximine (BSO). Incubation with Gd-Tex in the presence of ascorbate increased the aerobic radiation response of E89 and the apoptosis-sensitive B-cell line (LYAS). CONCLUSIONS: Gd-Tex sensitizes cells to ionizing radiation by increasing oxidative stress as a consequence of futile redox cycling. Optimization of the concentration of ascorbate (or other reducing species) may be required when evaluating Gd-Tex activity in vitro.

Animals↗
PubMed2001

Absence of Crabtree effect in human melanoma cells adapted to growth at low pH: reversal by respiratory inhibitors.

Because many tumors are acidic and hypoxic relative to normal tissues, glycolysis and oxygen consumption were investigated in early-passage human melanoma cells adapted to growth at pH 6.7. In the absence of glucose, the basal rate of oxygen consumption in low pH-adapted cells was 75% of that in cells grown at pH 7.3. The rate of lactic acid production in low pH-adapted cells was increased 4-fold by exposure to 16.7 mM glucose compared with a 10-fold increase in cells grown at pH 7.3. Furthermore, in low pH-adapted cells the rate of oxygen consumption was stimulated by the addition of glucose in contrast to the inhibition of oxygen consumption by elevated glucose in cells grown at pH 7.3 (i.e., the Crabtree effect). Both low pH-adapted cells and cells grown at pH 7.3 exposed to glucose plus 0.35 mM meta-iodo-benzylguanidine (MIBG), an inhibitor of mitochondrial respiration, had oxygen consumption reduced by approximately 60% and lactic acid production increased by approximately 65% relative to glucose alone. Although adaptation to growth at low pH was associated with a loss of the Crabtree effect and a higher ratio of oxygen consumption to lactic acid production, the rate of glycolysis was the same in both growth conditions in the presence of 0.1 mM dinitrophenol, an uncoupler of ATP synthesis. This indicates that the glycolytic capacity of low pH-adapted cells remains unchanged. Therefore, tumor acute acidification and oxygenation can be achieved by exposure to hyperglycemia combined with MIBG to improve therapeutic response.

3-Iodobenzylguanidine↗