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Biomedical subjects

Y C Cheng

Publications and source records attributed to Y C Cheng.

At least 19 recordsLinked to original sources
PubMed2006

Coherence in the B800 ring of purple bacteria LH2.

We study the quantum coherence in the B800 ring and how it affects the dynamics of excitation energy transfer (EET) in photo-synthetic light-harvesting systems. From an analysis of the spectrum, we determine the disorder parameters for the B800 ring and show that the relatively weak electronic coupling between B800 pigments subtly changes the dynamics of EET and improves the uniformity and robustness of B800 --> B850 EET at room temperature, an example of how a multichromophoric assembly can exploit coherence to optimize the efficiency of photosynthesis. A molecular-level description for the dynamics of EET in the light-harvesting system may prove useful for understanding other nanoscale molecular assemblies and designing efficient nanoscale optical devices.

Bacterial Proteins↗
PubMed2005

Markovian approximation in the relaxation of open quantum systems.

In this paper, we examine the validity of the Markovian approximation and the slippage scheme used to incorporate short time transient memory effects in the Markovian master equations (Redfield equations). We argue that for a bath described by a spectral function, J(omega), that is dense and smoothly spread out over the range omega(d), a time scale of tau(b) approximately 1/omega(d) exists; for times of t > tau(b), the Markovian approximation is applicable. In addition, if J(omega) decays to zero reasonably fast in both the omega --> 0 and omega --> infinity limits, then the bath relaxation time, tau(b), is determined by the width of the spectral function and is weakly dependent on the temperature of the bath. On the basis of this criterion of tau(b), a scheme to incorporate transient memory effects in the Markovian master equation is suggested. Instead of using slipped initial conditions, we propose a concatenation scheme that uses the second-order perturbation theory for short time dynamics and the Markovian master equation at long times. Application of this concatenation scheme to the spin-boson model shows that it reproduces the reduced dynamics obtained from the non-Markovian master equation for all parameters studied, while the simple slippage scheme breaks down at high temperatures.

Journal Article↗
PubMed2005

Neuroradiological findings in atypical teratoid/rhabdoid tumor of the central nervous system.

PURPOSE: To evaluate the computed tomography (CT) and magnetic resonance imaging (MRI) findings of atypical teratoid tumor/rhabdoid tumor (AT/RT) of the central nervous system (CNS). MATERIAL AND METHODS: Twenty cases of CNS AT/RT have been found over the past 23 years in our hospital; these involving 11 boys and 9 girls whose mean age at diagnosis was 5.5 years. Their clinical data, the CT, and MRI findings were reviewed retrospectively. RESULTS: AT/RT was located in the cerebellum in 15 cases. Four cases arose from the supratentorial region, while only one occurred primarily in the lumbar spinal cord. Almost all cases revealed heterogeneous intensity and heterogeneous enhancement. Peripheral cystic components were common. Survival time ranged from 2 months to 3 years, with a mean survival of 11.6 months. CONCLUSION: Most cases of AT/RT are located in the cerebellum. The radiologic manifestations are non-specific. The diagnosis mainly depends on the pathologic findings. However, AT/RT should still remain in the differential diagnosis of brain tumors in young children, especially those located in the cerebellar hemisphere and with eccentric cysts.

Adolescent↗
PubMed2004

Process modeling of the lipase-catalyzed dynamic kinetic resolution of (R, S)-suprofen 2,2,2-trifluoroethyl thioester in a hollow-fiber membrane.

A Candida rugosa lipase immobilized on polypropylene powder was employed as the biocatalyst for the enantioselective hydrolysis of (R, S)-suprofen 2,2,2-trifluorothioester in cyclohexane, in which trioctylamine was added as the catalyst to perform in situ racemization of the remaining (R)-thioester. A hollow-fiber membrane was also integrated with the dynamic kinetic resolution process in order to continuously extract the desired (S)-suprofen into an aqueous solution containing NaOH. A kinetic model for the whole process (operating in batch and feed-batch modes) was developed, in which enzymatic hydrolysis and deactivation, lipase activation, racemization and non-enantioselective hydrolysis of the substrate by trioctylamine, and reactive extraction of (R)- and (S)-suprofen into the aqueous phase in the membrane were considered. Theoretical predictions from the model for the time-course variations of substrate and product concentrations in each phase were compared with experimental data.

Amines↗
PubMed2002

Animal models for the study of HBV infection and the evaluation of new anti-HBV strategies.

BACKGROUND: Our aim was to evaluate the anti-HBV activity of a novel L-nucleoside analog, 2',3'-dideoxy-2',3'-didehydro-beta-L-5-fluorocytidine (beta-L-Fd4C), in study models of HBV infection. METHOD: Its mechanism of action was evaluated on the in vitro expressed duck HBV (DHBV) reverse transcriptase and in primary hepatocyte cultures of duck and human origin. The capacity of antiviral therapy to clear viral infection was analyzed in vivo in the duck and woodchuck models. RESULTS: beta-L-Fd4C-TP exhibited a more potent inhibitory effect on the RT activity of the DHBV polymerase than other cytidine analogs (lamivudine-TP, ddC-TP, beta-L-FddC-TP). In primary duck hepatocyte cultures, beta-L-Fd4C exhibited a long-lasting inhibitory effect on viral DNA synthesis but could not clear viral cccDNA. In vivo treatment with beta-L-Fd4C in infected ducklings and woodchucks, induced a greater suppression of viremia and intrahepatic viral DNA synthesis than with lamivudine. However, covalently closed circular DNA persistence explained the relapse of viral replication after treatment withdrawal. Viral spread was strongly reduced in the case of early therapeutical intervention, but the number of infected cells did not decline when therapy was started during chronic infection. Liver histology analysis showed a decrease in the inflammatory activity of chronic hepatitis while no ultrastructural modification of liver cells was observed in electron microscopy studies. Furthermore, in human primary hepatocyte cultures, beta-L-Fd4C induced a significant inhibition of HBV DNA synthesis. CONCLUSION: beta-L-Fd4C is a potent inhibitor of hepadnavirus RT and inhibits viral DNA synthesis in hepatocytes both in vitro and in vivo. These experimental studies allowed as to show that beta-L-Fd4C is a promising anti-HBV agent. Combination therapy should be evaluated to eradicate viral infection.

Animals↗
PubMed2001

Sox8 gene expression identifies immature glial cells in developing cerebellum and cerebellar tumours.

Sox8 is a member of the E subgroup of Sox genes, the other members of which are Sox9 and Sox10, both of which are implicated in specific human disorders. Recently, Sox8 homologues have been cloned in chick, mouse and human and have been shown to be strongly expressed in the embryonic and adult brain. Nevertheless, the cell types that express Sox8 have not been determined. We show here that Sox8 is expressed in immature glia in the developing cerebellum. Sox8 is also expressed in scattered cells in the cerebellar tumour, medulloblastoma. This gene therefore provides an early glial marker that may provide more detailed insight into the cellular makeup and consequent behaviour of medulloblastomas.

Animals↗
PubMed2001

Dysfunctional regulation of endothelial nitric oxide synthase (eNOS) expression in response to exercise in mice lacking one eNOS gene.

BACKGROUND: Previous data suggest that 1 endothelial NO synthase (eNOS) gene is sufficient to allow normal expression and function of eNOS under basal conditions. We hypothesized that this might not hold true for conditions known to increase eNOS gene expression, such as exercise. METHODS AND RESULTS: Male mice heterozygous for a disruption of the eNOS gene (eNOS(+/)(-)) and normal C56Bl/6J mice (eNOS(+/+)), 3 to 4 months of age, underwent exercise training for 3 weeks. Nontrained mice were exposed to the exercise environment (noise and vibration of the treadmill) without exercise for an identical period. In eNOS(+/+) mice (n=7), exercise increased aortic eNOS protein expression by 3.4+/-0.4-fold (P<0.002). This was associated with a greater vascular cGMP accumulation on stimulation with acetylcholine (P<0.05). Furthermore, exercise training increased eNOS mRNA (1.78+/-0.4-fold) and protein (1.76+/-0.17-fold) in left ventricular tissue, as determined by competitive reverse transcription-polymerase chain reaction and Western analysis (P<0.05 for both). In striking contrast, exercise had no effect on aortic eNOS expression and cGMP accumulation in eNOS(+/)(-) mice (P>0.05). Thus, although eNOS expression appears to be normal in eNOS(+/)(-) mice under basal conditions, these mice are unable to increase eNOS expression during exercise. CONCLUSIONS: These findings show that regulation of eNOS expression during exercise requires the presence of both alleles of the gene and may have implications for conditions in which polymorphisms of eNOS are present in only 1 allele in humans. These individuals may have a normal vascular reactivity under basal conditions but may be unable to adapt their vascular reactivity in response to exercise training.

Animals↗
PubMed2001

Jac1, a mitochondrial J-type chaperone, is involved in the biogenesis of Fe/S clusters in Saccharomyces cerevisiae.

A minor Hsp70 chaperone of the mitochondrial matrix of Saccharomyces cerevisiae, Ssq1, is involved in the formation or repair of Fe/S clusters and/or mitochondrial iron metabolism. Here, we report evidence that Jac1, a J-type chaperone of the mitochondrial matrix, is the partner of Ssq1 in this process. Reduced activity of Jac1 results in a decrease in activity of Fe/S containing mitochondrial proteins and an accumulation of iron in mitochondria. Fe/S enzyme activities remain low in both jac1 and ssq1 mutant mitochondria even if normal mitochondrial iron levels are maintained. Therefore, the low activities observed are not solely due to oxidative damage caused by excess iron. Rather, these molecular chaperones likely play a direct role in the normal assembly process of Fe/S clusters.

Aconitate Hydratase↗
PubMed2001

Application of the SUSHI method to the design of gradient coils.

An approach to potential improvements in magnetic field shielding for a gradient coil system with cylindrical geometry is presented, utilizing "supershielding" conditions for the currents on both the primary and the secondary coils. It is demonstrated that the field can be strongly suppressed everywhere outside a cylindrical shield coil radius, even though the finite-length active shield only partially surrounds a primary coil. The supershielding method, which is aimed at controlling eddy currents, still has sufficient freedom to maintain the desired magnetic field behavior inside the imaging volume. The trade-off is an additional primary current oscillation and increased current peaks and field energy. This method has been applied to design short transverse and axial gradient coils, giving substantially improved shielding compared to an apodization method. Magn Reson Med 45:147-155, 2001.

Equipment Design↗
PubMed2001

Prenatal diagnosis of cleft palate by three-dimensional ultrasound.

Prenatal diagnosis of cleft palate is very important to prenatal consultation and management after birth. To examine if three-dimensional (3-D) ultrasound (US) is an accurate diagnostic method for clinical use, we analyzed our experience in detecting cleft palate by 3-D US. From June 1996 to January 2000, 21 fetuses with facial clefts were scanned by 2-D US, as well as by 3-D US. The coronal and oblique planes were reconstructed by 3-D US to detect the cleft palate. In addition, level II US was performed to find any possibly associated anomalies. All the scans were recorded on optic disks for final analysis. In our study, the gestational age when prenatal diagnosis was made by US initially was between 20 and 34 weeks. The accuracy for prenatal diagnosis of cleft lip with or without cleft palate by 3-D US was 100%, which was superior to that by 2-D US (p < 0.05). In addition, we proposed a novel method to evaluate the cleft palate systemically by 3-D US. In conclusion, from our study, fetuses with cleft lip combined with or without cleft palate can be easily differentiated by 3-D US. The reconstruction of coronal and oblique planes by 3-D US is a powerful tool for detecting cleft palate.

Cleft Lip↗
PubMed2001

Potential use of antiviral L(-)nucleoside analogues for the prevention or treatment of viral associated cancers.

Several types of virus were found to have a strong association with different types of cancers. Thus, a selective antiviral compound without toxicity upon long-term usage will be useful not only for the treatment of viral diseases but also for the prevention or the delayed onset of those cancers, which have a strong association with viruses. L(-)Nucleoside analogs were discovered recently in my laboratory as an important class of antiviral and anticancer chemical entities. L(-)SddC (3TC, Lamivudine), FTC, Fd4C, and L(-)FMAU are potent anti-HBV compounds with different pharmacological profiles. These compounds may be useful in the prevention or delayed onset of hepatocellular carcinoma associated with HBV. L(-)I-OddU is the most potent anti-Epstein-Barr Virus (EBV) compound without cytotoxicity and animal toxicity upon long-term dosing which gives the pharmacological levels of the drug in plasma. This compound may have the potential to prevent B-cell lymphoma associated with patients undergoing organ transplants in addition to its potential use for the treatment of EBV infection.

Animals↗
PubMed2001

An exact form for the magnetic field density of states for a dipole.

We present an analytical form for the density of states for a magnetic dipole in the center of a spherical voxel. This analytic form is then used to evaluate the signal decay as a function of echo time for different volume fractions and susceptibilities. The decay can be considered exponential only in a limited interval of time. Otherwise, it has a quadratic dependence on time for short echo times and an oscillatory decaying behavior for long echo times.

Humans↗
PubMed2001

Were there enough physicians in an emergency department in the affected area after a major earthquake? An analysis of the Taiwan Chi-Chi earthquake in 1999.

STUDY OBJECTIVE: The purpose of this study was to evaluate physician manpower and mobilization in an urban emergency department receiving patients after a major earthquake. METHODS: Patient charts were reviewed. The workload of physicians was assessed semiquantitatively before and after a major earthquake. The physicians' mobilization in the postearthquake emergency response was assessed by using a confidential questionnaire. RESULTS: In the 3 days after the earthquake, 566 patients with earthquake-related illnesses or injuries were sent to the urban ED. Three hundred one (53.2%) patients arrived within the initial 10 hours. In the initial hours, there was no significant difference between the number of patients per physician per hour before and after the earthquake. Workloads of wound treatment and advanced life support procedures were significantly higher after the earthquake compared with before the earthquake, during the first to sixth hour and second to fifth hour, respectively. Sixty-five percent of the hospital's physicians did not assist in either the ED or in any other parts of the hospital in the initial 6 hours after the earthquake. CONCLUSION: The number of physicians in the ED was insufficient in the initial hours after the earthquake because of the sudden influx of a large number of patients. Future disaster planning must address the issue of physicians' behavior with regard to their priorities immediately after a major earthquake and include greater provision for efficient mobilization of physicians.

Disasters↗
PubMed2001

Synthesis of halogen-substituted 3-deazaadenosine and 3-deazaguanosine analogues as potential antitumor/antiviral agents.

Various 2-halogen-substituted analogues (38, 39, 43 and 44), 3-halogen-substituted analogues (51 and 52), and 2',3'-dihalogen-substituted analogues (57-60) of 3-deazaadenosine and 3-halogen-substituted analogues (61 and 62) of 3-deazaguanosine have been synthesized as potential anticancer and/or antiviral agents. Among these compounds, 3-deaza-3-bromoguanosine (62) showed significant cytotoxicity against L1210, P388, CCRF-CEM and B16F10 cell lines in vitro, producing IC50 values of 3, 7, 9 and 7 microM, respectively. Several 3-deazaadenosine analogues (38, 51, 57 and 59) showed moderate to weak activity against hepatitis B virus.

Animals↗
PubMed2001

Successful pregnancy by transmyometrial and transtubal embryo transfer after IVF in a patient with congenital cervical atresia who underwent uterovaginal canalization during Caesarean section: case report.

Successful pregnancy in a patient with congenital cervical atresia is a great challenge for assisted reproductive techniques and reproductive medicine. We report a case of successful pregnancy by transmyometrial and transtubal embryo transfer simultaneously after in-vitro fertilization (IVF) in a 33 year-old patient with congenital cervical atresia diagnosed at the age of 18 years. The patient had experienced cyclic abdominal pain and amenorrhoea since she was 13 years old. She had had two unsuccessful attempts to create a new uterovaginal canal in another hospital. At the age of 32 years, she was referred to our unit and had a successful pregnancy after transmyometrial and transtubal embryo transfer. Caesarean section was performed at 36 weeks gestation due to progressive pre-eclampsia and gestational diabetes. A healthy male baby weighing 2812 g was safely delivered. Uterovaginal canalization with amniotic membrane for the covering of the neo-endocervical wall was performed during Caesarean section. Normal menstrual outflow and symptomatic relief have continued for 5 months after the operation. To the best of our knowledge, this is the first reported case of successful pregnancy by transmyometrial and transtubal embryo transfer as well as uterovaginal canalization performed during Caesarean section in a patient with congenital cervical atresia.

Amnion↗