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Biomedical subjects

Y C Lai

Publications and source records attributed to Y C Lai.

At least 37 records · Page 2Linked to original sources
PubMed2001

Evaluation of immunomagnetic separation method for detection of Giardia for different reaction times and reaction volumes.

Immunomagnetic separation (IMS) has been specified as a standard method for the measurement of Giardia. In this study, Dynal IMS was evaluated on the basis of recovery efficiencies of Giardia cysts for various IMS operational conditions. The average recoveries for Giardia in deionized, treated and raw water samples were 82.6 +/- 12.2% (n = 6), 75.6 +/- 15.2% (n = 3), and 70.6 +/- 18.2% (n = 3), respectively. Significant changes in recovery were observed by altering the debris ratio and the debris components of water samples. Changing the reaction volume within the same vessel had no significant effect on cyst recovery efficiencies. However, prolonging the reaction time did increase recovery efficiencies.

Animals↗
PubMed2001

Observations on the application of the correlation dimension and correlation integral to the prediction of seizures.

The authors reexamine the correlation integral and the related correlation dimension in the context of EEG analysis with application to seizure prediction. They identify dependencies of the correlation integral and the correlation dimension on frequency and amplitude of the signal, which may result in a reinterpretation of the dynamic importance of these measures and may cast doubts on their predictive abilities for certain classes of seizures. The relevance, for clinical and research purposes, of the distinction between retrospective and prospective inference (prediction) is addressed briefly. The authors point to the need for further research, consisting of long time series, containing multiple seizures, and for the development of objective prediction criteria.

Cerebral Cortex↗
PubMed2001

Identification of genes induced in vivo during Klebsiella pneumoniae CG43 infection.

A novel in vivo expression technology (IVET) was performed to identify Klebsiella pneumoniae CG43 genes that are specifically expressed during infection of BALB/c mice. The IVET employed a UDP glucose pyrophosphorylase (galU)-deficient mutant of K. pneumoniae which is incapable of utilizing galactose and synthesizing capsular polysaccharide, as demonstrated by its low virulence to BALB/c mice and a white nonmucoid colony morphology on MacConkey-galactose agar. By using a functional galU gene as the reporter, an IVE promoter could render the galU mutant virulent while maintaining the white nonmucoid colony phenotype. A total of 20 distinct sequences were obtained through the in vivo selection. Five of them have been identified previously as virulence-associated genes in other pathogens, while another five with characterized functions are involved in regulation and transportation of nutrient uptake, biosynthesis of isoprenoids, and protein folding. No known functions have been attributed to the other 10 sequences. We have also demonstrated that 2 of the 20 IVE genes turn on under iron deprivation, whereas the expression of another five genes was found to be activated in the presence of paraquat, a superoxide generator.

Animals↗
PubMed2001

Endoscopic ultrasonography to study the causes of extragastric compression mimicking gastric submucosal tumor.

BACKGROUND AND PURPOSE: Many reports have confirmed that endoscopic ultrasonography (EUS) can differentiate gastric submucosal tumor from extragastric compression, but only a few specifically concentrated on EUS in identifying the causes of external compression. MATERIALS AND METHODS: From May 1993 to May 2001, we used EUS in 238 patients to diagnose gastric submucosal tumor or external compression. We excluded 183 patients who had submucosal tumors and analyzed the remaining 55 patients with extragastric compression. Malignant causes of external compression were proved by surgery or biopsy. Benign causes of external compression were proved by other imaging examinations (abdominal ultrasound, computerized tomography, angiography) or surgery. Patients with external compression caused by normal organs were followed up with repeated upper gastrointestinal endoscopy or EUS. RESULTS: The stomach was compressed by normal extragastric organs in 32 patients (spleen 10, splenic vessel 6, gall bladder 9, liver 3, pancreas 3, and intestine 1), by benign pathologic lesions in 12 patients (liver cyst 7, liver hemagioma 2, splenic cyst 1, pancreatic cyst 1, pancreatic cystadenoma 1) and by malignant tumors in 5 patients (hepatoma 1, liver metastasis from colon cancer 2, pancreatic cystadenocarcinoma 1 and lymphoma of spleen 1). In the remaining six patients, neither submucosal tumor nor external compression was found during EUS examination and the external compression was considered transient. CONCLUSION: When an extragastric compression mimicking submucosal tumor is detected by upper gastrointestinal endoscopy, EUS is indicated to identify the cause of extragastric compression.

Adolescent↗
PubMed2000

Identification of genes present specifically in a virulent strain of Klebsiella pneumoniae.

Klebsiella pneumoniae is a common cause of septicemia and urinary tract infections. The PCR-supported genomic subtractive hybridization was employed to identify genes specifically present in a virulent strain of K. pneumoniae. Analysis of 25 subtracted DNA clones has revealed 19 distinct nucleotide sequences. Two of the sequences were found to be the genes encoding the transposase of Tn3926 and a capsule polysaccharide exporting enzyme. Three sequences displayed moderate homology with bvgAS, which encodes a two-component signal transduction system in Bordetella pertussis. The rest of the sequences did not exhibit homology with any known genes. The distribution of these novel sequences varied greatly in K. pneumoniae clinical isolates, reflecting the heterogeneous nature of the K. pneumoniae population.

Bacterial Proteins↗
PubMed1999

UV inducibility of rat proliferating cell nuclear antigen gene promoter.

Proliferating cell nuclear antigen (PCNA), also known as a cofactor of DNA polymerase delta, is required for eukaryotic cell DNA synthesis and nucleotide excision repair. Expression of PCNA gene is growth-regulated and UV inducible. In our previous study, we have observed that the rat PCNA promoter has the serum responsiveness. In this study, we demonstrate its UV inducibility in CHO.K1 cells. The UV induction of the rat PCNA promoter activity was dose-dependent in the cells synchronized at different phases. In addition, the sequences of the promoter responsible for the UV inducibility were delimited to the region between nucleotides -70 and +125, which contains an AP-1 site and a downstream proximal ATF/CRE site. While mutation of the AP-1 site abrogated the UV inducibility, mutation of the ATF/CRE site enhanced the UV inducibility, suggesting that the two sites play different roles in the UV induction of the promoter. In addition, the role of p53 in the UV induction of rat PCNA promoter was investigated. We found that exogenous p53 was unable to mimic the UV irradiation to induce rat PCNA promoter and that the UV induction of the rat PCNA promoter was seen in p53 deficient cells. Therefore, it is unlikely that the UV induction of the rat PCNA promoter is p53 dependent.

Animals↗
PubMed1999

Function and sequence analyses of tumor suppressor gene p53 of CHO.K1 cells.

The tumor suppressor gene p53 plays an important role in guarding genomic integrity. When induced in response to environmental results, the gene product of p53 functions as a transcription factor to transactivate genes involved in arresting the cell cycle and as a facilitator of DNA repair. In contrast, the status of p53 in Chinese hamster ovary (CHO) cells, commonly used as a model system for various studies including those involving the cell cycle and transformation, remains an enigma. In this study, the function and sequence of p53 in CHO.K1 cells were investigated. The level of p53 proteins was elevated on ultraviolet (UV) irradiation of the cells, and the proteins formed specific complexes as probed with DNA containing p53-binding sequences. Its activities toward responsive promoters were inducible by UV in a dose-dependent manner. Although p53 in CHO.K1 contained a single missense mutation at codon 211, the mutation apparently had no effect on the functional properties of the protein. The CHO.K1 cells on X-ray irradiation failed to arrest at G1 phase even when the cells were transfected with a wildtype human p53 gene, indicating that the failure probably was not caused by dysfunction of its p53, but by some other mechanism. This result is consistent with the finding that p21(Waf1/Cip1) is undetectable in UV-treated CHO.K1 cells, whereas Gadd45 is induced by UV light in the cells.

3T3 Cells↗
PubMed1999

Universal behavior in the parametric evolution of chaotic saddles.

Chaotic saddles are nonattracting dynamical invariant sets that physically lead to transient chaos. As a system parameter changes, chaotic saddles can evolve via an infinite number of homoclinic or heteroclinic tangencies of their stable and unstable manifolds. Based on previous numerical evidence and a rigorous analysis of a class of representative models, we show that dynamical invariants such as the topological entropy and the fractal dimension of chaotic saddles obey a universal behavior: they exhibit a devil-staircase characteristic as a function of the system parameter.

Journal Article↗
PubMed1999

Observability of lag synchronization of coupled chaotic oscillators.

Lag synchronization is a recently discovered theoretical phenomenon where the dynamical variables of two coupled, nonidentical chaotic oscillators are synchronized with a time delay relative to each other. We investigate experimentally and numerically to what extent lag synchronization can be observed in physical systems where noise is inevitable. Our measurements and numerical computation suggest that lag synchronization is typically destroyed when the noise level is comparable to the amount of average system mismatch. At small noise levels, lag synchronization occurs in an intermittent fashion.

Journal Article↗
PubMed1999

Transient fractal behavior in snapshot attractors of driven chaotic systems.

Snapshot attractors, i.e., attractors formed by a cloud of trajectories at the same instants of time, are usually employed to reveal the fractal structure of randomly or chaotically driven dynamical systems. A necessary condition for the underlying fractal structure to be observed is that the ensemble of particles utilized in the construction of the snapshot attractors are subject to identical perturbation at any instant of time. We examine the influence of small phase-space inhomogeneity in the chaotic perturbation on the observability of the snapshot fractal attractors. We find that, typically, fractal structure can be seen in only a transient period of time. The scaling of the transient time with the amount of inhomogeneity is investigated. Implication to experimental observation of fractal structure in physical systems is pointed out.

Journal Article↗
PubMed1999

Unstable dimension variability in coupled chaotic systems.

Systems of coupled chaotic maps and flows arise in many situations of physical and biological interest. The aim of this paper is to analyze and to present numerical evidence for a common type of nonhyperbolic behavior in these systems: unstable dimension variability. We show that unstable periodic orbits embedded in the dynamical invariant set of such a system can typically have different numbers of unstable directions. The consequence of this may be severe: the system cannot be modeled deterministically in the sense that no trajectory of the model can be realized by the natural chaotic system that the model is supposed to describe and quantify. We argue that unstable dimension variability can arise for small values of the coupling parameter. Severe modeling difficulties, nonetheless, occur only for reasonable coupling when the unstable dimension variability is appreciable. We speculate about the possible physical consequences in this case.

Journal Article↗
PubMed1999

Efficient algorithm for detecting unstable periodic orbits in chaotic systems.

We present an efficient method for fast, complete, and accurate detection of unstable periodic orbits in chaotic systems. Our method consists of an iterative scheme and an effective technique for selecting initial points. The iterative scheme is based on the semi-implicit Euler method, which has both fast and global convergence, and only a small number of initial points is sufficient to detect all unstable periodic orbits of a given period. The power of our method is illustrated by numerical examples of both two- and four-dimensional maps.

Journal Article↗
PubMed1999

Unstable periodic orbits and the natural measure of nonhyperbolic chaotic saddles.

Chaotic saddles are nonattracting dynamical invariant sets that physically lead to transient chaos. We examine the characterization of the natural measure by unstable periodic orbits for nonhyperbolic chaotic saddles in dissipative dynamical systems. In particular, we compare the natural measure obtained from a long trajectory on the chaotic saddle to that evaluated from unstable periodic orbits embedded in it. Our systematic computations indicate that the periodic-orbit theory of the natural measure, previously shown to be valid only for hyperbolic chaotic sets, is applicable to nonhyperbolic chaotic saddles as well.

Journal Article↗
PubMed1999

Abrupt bifurcation to chaotic scattering with discontinuous change in fractal dimension.

One of the major routes to chaotic scattering is through an abrupt bifurcation by which a nonattracting chaotic saddle is created as a system parameter changes through a critical value. In a previously investigated case, however, the fractal dimension of the set of singularities in the scattering function changes continuously through the bifurcation. We describe a type of abrupt bifurcation to chaotic scattering where this physically relevant dimension changes discontinuously at the bifurcation. The bifurcation is illustrated using a class of open Hamiltonian systems consisting of Morse potential hills.

Journal Article↗
PubMed1999

Endoscopic ultrasonography in the differential diagnosis of giant gastric folds.

Giant gastric folds (or large gastric folds) are found in both benign and malignant diseases, and differential diagnosis with either upper gastrointestinal X-ray or endoscopy is difficult. Sometimes, even endoscopic biopsy cannot establish a definitive diagnosis. Recently, endoscopic ultrasonography (EUS) has been used to study giant gastric folds. We performed EUS in 25 patients with giant gastric folds that had been detected with upper gastrointestinal X-ray or endoscopy. The definitive diagnoses were confirmed by histopathology, other examinations, or long-term follow-up. The final diagnoses of these 25 patients were gastric varices in eight, gastric lymphangiectasis in one, gastritis in four, gastric carcinoma (scirrhous type) in six, and gastric lymphomas in six. All patients with gastric varices had anechoic tortuous varicose veins in the submucosal layer. EUS images of gastric lymphangiectasis were similar to those of gastric varices. EUS revealed regular gastric wall thickening of the second (mucosa) and third (submucosa) layers in all cases of gastritis. The fourth (muscularis propria) layer was intact in the only case of mucosa-associated lymphoid tissue lymphoma (MALToma), but not in the other five cases of gastric lymphoma. The second and third layers of this MALToma were irregular in thickness and heterogenous in echogenicity, different from the characteristic EUS findings in gastritis. The fourth layer was markedly thickened only in malignant conditions. Differentiation of gastric cancer from lymphoma with EUS was difficult because of overlapping EUS findings. In conclusion, EUS is indicated for the differential diagnosis of giant gastric folds. In addition, it avoids the risk associated with biopsy of gastric varices.

Adult↗
PubMed1998

Serum responsiveness of the rat PCNA promoter involves the proximal ATF and AP-1 sites.

We have previously shown that the rat PCNA (proliferating cell nuclear antigen) gene promoter is responsive to serum stimulation. In this study, the sequence of the promoter responsive to serum stimulation has been localized in the region between nucleotides -70 and +125 relative to the transcription initiation site. This region contains an ATF site (nucleotides -51 to -44) and an AP-1 site (nucleotides -64 to -58). Mutation at either the ATF or the AP-1 site reduced the serum responsiveness of the promoter. In gel mobility shift assays, nuclear extracts from serum stimulated cells, compared to those from quiescent cells, exhibit an increasing binding activity toward a promoter related oligonucleotide (-70 to -42) which includes the ATF site and the AP-1 site. Formation of the DNA:protein complexes requires the simultaneous involvement of ATF and AP-1 sites as either element can abrogate the complexes in the competition experiment. Both the distance and sequence are essential to complex formation. Moreover, ATF-1 but not ATF-2 (or CREB) has been identified as a major component of the complexes in the antibody supershift or interference experiment. The results of this study suggest that ATF-1 in association with other factors is involved in regulating the serum stimulation of the rat PCNA promoter activity via the proximal ATF and AP-1 sites.

Activating Transcription Factors↗
PubMed1998

Bladder shape impact on the accuracy of ultrasonic estimation of bladder volume.

OBJECTIVE: Variations in bladder shape can lead to errors in ultrasonic estimation of the bladder volume. The purposes of this study were to compare the accuracies of various formulas to estimate bladder volume from sonographic measurements and to assess the impact of bladder shape on the accuracy of bladder volume estimation. STUDY DESIGN: Twenty-four healthy volunteers (13 men, 11 women) and 55 spinal cord injury patients (48 men, 7 women) underwent ultrasonographic measurements of dimensions before and after voiding. Bladder shape was classified as cuboid, ellipsoid, or triangular prism. Ten formulas from the literature were applied to estimate bladder volume, using the volume voided or catheterized as the standard, and then linear regression was used to obtain optimal correction coefficients for the whole data set as well as each of the three bladder shapes. SETTING: Rehabilitation hospital affiliated with a medical college. RESULTS: The most accurate of the 10 formulas tested was height (H) X transverse depth (Dt) x weight (W) x 0.7 (mean error 17.4%+/-11.6%). Linear regression analysis yield optimal correction coefficients of .72 for the whole data set and .89, .81, and .66 for cuboidal, ellipsoid, and triangular prism-shaped bladders, respectively. The mean error for the estimation of bladder volume using .72 as the correction coefficient was 16.9%+/-11.9% and decreased to 12.7%+/-10.1% (p < .0001, paired t test) when the bladder shape was taken into account. CONCLUSION: Using bladder shape for reference and applying the corresponding correction coefficient to volume calculations will improve the accuracy of the estimation.

Adult↗