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436 results on '"Cheung, C. Y."'

4. H5N1 Influenza: A Protean Pandemic Threat

Author

Guan, Y., Poon, L. L. M., Cheung, C. Y., Ellis, T. M., Lim, W., Lipatov, A. S., Chan, K. H., Sturm-Ramirez, K. M., Cheung, C. L., Leung, Y. H. C., Yuen, K. Y., Webster, R. G., and Peiris, J. S. M.

Published
2004

6. $B -> \pi l \nu$ Form Factors Calculated on the Light-Front

Author

Cheung, C. Y., Hwang, C. W., and Zhang, W. M.

Subjects
High Energy Physics - Phenomenology
Abstract

A consistent treatment of $B\rightarrow \pi l \nu$ decay is given on the light-front. The $B$ to $\pi$ transition form factors are calculated in the entire physical range of momentum transfer for the first time. The valence-quark contribution is obtained using relativistic light-front wave functions. Higher quark-antiquark Fock-state of the $B$-meson bound state is represented effectively by the $|B^*\pi\rangle$ configuration, and its effect is calculated in the chiral perturbation theory. Wave function renormalization is taken into account consistently. The $|B^*\pi\rangle$ contribution dominates near the zero-recoil point ($q^2\simeq 25$ GeV$^2$), and decreases rapidly as the recoil momentum increases. We find that the calculated form factor $f_+(q^2)$ follows approximately a dipole $q^2$-dependence in the entire range of momentum transfer., Comment: Revtex, 19 pages, 9 figures

Published
1996
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8. Corrections to Chiral Dynamics of Heavy Hadrons: (I) 1/M Correction

Author

Cheng, H. Y., Cheung, C. Y., Lin, G. L., Lin, Y. C., Yan, T. M., and Yu, H. L.

Subjects
High Energy Physics - Phenomenology
Abstract

In earlier publications we have analyzed the strong and radiative decays of heavy hadrons in a formalism which incorporates both heavy-quark and chiral symmetries. In particular, we have derived a heavy-hadron chiral Lagrangian whose coupling constants are related by the heavy-quark flavor-spin symmetry arising from the QCD Lagrangian with infinitely massive quarks. In this paper, we re-examine the structure of the above chiral Lagrangian by including the effects of $1/m_Q$ corrections in the heavy quark effective theory. The relations among the coupling constants, originally derived in the heavy-quark limit, are modified by heavy quark symmetry breaking interactions in QCD. Some of the implications are discussed., Comment: PHYZZX, 45 pages, 1 figure (not included), CLNS 93/1192, IP-ASTP-02-93, ITP-SB-93-04

Published
1993
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9. Heavy Quark and Chiral Symmetry Predictions for Semileptonic Decays B->D(D*),pi,l,nu

Author

Cheng, H-Y, Cheung, C-Y, Dimm, W., Lin, G-L, Lin, Y. C., Yan, T-M, and Yu, H-L

Subjects
High Energy Physics - Phenomenology
Abstract

We study in detail the prediction for the semileptonic decays $\bar{B} \to D (D^*) \pi \ell \bar{\nu}$ by heavy quark and chiral symmetry. The branching ratio for $\bar{B} \to D \pi \ell \bar{\nu}$ is quite significant, as big as $(0.5-1)\%$. The branching ratio for $\bar{B} \to D^* \pi \ell \bar{\nu}$ is only of order $10^{-4}-10^{-5}$. Numerical results for various single particle spectra and their dependence on the pion momentum cutoff schemes are presented in a series of figures, as are the model independent ratios for differential rates of $D$ and $D^*$. We also study the parity-violation effects on the decay rates for different polarization states of the $D^*$. Figures may be obtained by anonymous FTP from strange.tn.cornell.edu in the directory pub/CLNS931204, or by email from the author., Comment: 28 pages, 23 figs (FTP from author), LaTeX, Typos corrected in Eq. 4.9c (factor of 2), Eq. A.4, and Tables II & III. No change in content, results, or figures. CLNS93/1204, IP-ASTP-15-93

Published
1993
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11. Chiral Lagrangians for Radiative Decays of Heavy Hadrons

Author

Cheng, H. Y., Cheung, C. Y., Lin, G. L., Lin, Y. C., Yan, T. M., and Yu, H. L.

Subjects
High Energy Physics - Phenomenology
Abstract

The radiative decays of heavy mesons and heavy baryons are studied in a formalism which incorporates both the heavy quark symmetry and the chiral symmetry. The chiral Lagrangians for the electromagnetic interactions of heavy hadrons consist of two pieces: one from gauging electromagnetically the strong-interaction chiral Lagrangian, and the other from the anomalous magnetic moment interactions of the heavy baryons and mesons. Due to the heavy quark spin symmetry, the latter contains only one independent coupling constant in the meson sector and two in the baryon sector. These coupling constants only depend on the light quarks and can be calculated in the nonrelativistic quark model. However, the charm quark is not heavy enough and the contribution from its magnetic moment must be included. Applications to the radiative decays $D^\ast \rightarrow D \gamma~,~B^\ast \rightarrow B \gamma~,~ \Xi^\prime_c \rightarrow \Xi_c \gamma~, \Sigma_c \rightarrow \Lambda_c \gamma$ and $\Sigma_c \rightarrow \Lambda_c \pi \gamma$ are given. Together with our previous results on the strong decay rates of $D^\ast \rightarrow D \pi$ and $\Sigma_c \rightarrow \Lambda_c \pi$, predictions are obtained for the total widths and branching ratios of $D^\ast$ and $\Sigma_c$. The decays $\Sigma^+_c \rightarrow \Lambda^+_c \pi^0 \gamma $ and $\Sigma^0_c \rightarrow \Lambda^+_c \pi^- \gamma $ are discussed to illustrate the important roles played by both the heavy quark symmetry and the chiral symmetry., Comment: 30 pages (one figure, available on request), CLNS 92/1158 and IP-ASTP-13-92

Published
1992
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19. Synthetic Sansanmycin Analogues as Potent Mycobacterium tuberculosis Translocase I Inhibitors

Author

Tran, W, Kusay, AS, Hawkins, PME, Cheung, C-Y, Nagalingam, G, Pujari, V, Ford, DJ, Stoye, A, Ochoa, JL, Audette, RE, Hortle, E, Oehlers, SH, Charman, SA, Linington, RG, Rubin, EJ, Dowson, CG, Roper, DI, Crick, DC, Balle, T, Cook, GM, Britton, WJ, and Payne, RJ

Subjects
Bacterial Proteins, Medicinal & Biomolecular Chemistry, 0304 Medicinal and Biomolecular Chemistry, 0305 Organic Chemistry, 1115 Pharmacology and Pharmaceutical Sciences, Antitubercular Agents, Animals, Transferases (Other Substituted Phosphate Groups), Mycobacterium tuberculosis, Enzyme Inhibitors, bacterial infections and mycoses, Hydrophobic and Hydrophilic Interactions, Oligopeptides, Uridine, Zebrafish
Abstract

Herein, we report the design and synthesis of inhibitors of Mycobacterium tuberculosis (Mtb) phospho-MurNAc-pentapeptide translocase I (MurX), the first membrane-associated step of peptidoglycan synthesis, leveraging the privileged structure of the sansanmycin family of uridylpeptide natural products. A number of analogues bearing hydrophobic amide modifications to the pseudo-peptidic end of the natural product scaffold were generated that exhibited nanomolar inhibitory activity against Mtb MurX and potent activity against Mtb in vitro. We show that a lead analogue bearing an appended neopentylamide moiety possesses rapid antimycobacterial effects with a profile similar to the frontline tuberculosis drug isoniazid. This molecule was also capable of inhibiting Mtb growth in macrophages where mycobacteria reside in vivo and reduced mycobacterial burden in an in vivo zebrafish model of tuberculosis.

Published
2021

27. Discovery of Cephalosporin-3'-Diazeniumdiolates That Show Dual Antibacterial and Antibiofilm Effects against Pseudomonas aeruginosa Clinical Cystic Fibrosis Isolates and Efficacy in a Murine Respiratory Infection Model

Author

Rineh, A, Soren, O, McEwan, T, Ravikumar, V, Poh, WH, Azamifar, F, Naimi-Jamal, MR, Cheung, C-Y, Elliott, AG, Zuegg, J, Blaskovich, MAT, Cooper, MA, Dolange, V, Christodoulides, M, Cook, GM, Rice, SA, Faust, SN, Webb, JS, and Kelso, MJ

Subjects
1108 Medical Microbiology
Abstract

The formation of biofilms provides a formidable defense for many bacteria against antibiotics and host immune responses. As a consequence, biofilms are thought to be the root cause of most chronic infections, including those occurring on medical indwelling devices, endocarditis, urinary tract infections, diabetic and burn wounds, and bone and joint infections. In cystic fibrosis (CF), chronic Pseudomonas aeruginosa (P. aeruginosa) respiratory infections are the leading cause of morbidity and mortality in adults. Previous studies have shown that many bacteria can undergo a coordinated dispersal event in the presence of low concentrations of nitric oxide (NO), suggesting that NO could be used to initiate biofilm dispersal in chronic infections, enabling clearance of the more vulnerable planktonic cells. In this study, we describe efforts to create "all-in-one" cephalosporin-based NO donor prodrugs (cephalosporin-3'-diazeniumdiolates, C3Ds) that show both direct β-lactam mediated antibacterial activity and antibiofilm effects. Twelve novel C3Ds were synthesized and screened against a panel of P. aeruginosa CF clinical isolates and other human pathogens. The most active compound, AMINOPIP2 ((Z)-1-(4-(2-aminoethyl)piperidin-1-yl)-2-(((6R,7R)-7-((Z)-2-(2-aminothiazol-4-yl)-2-(((2-carboxypropan-2-yl)oxy)imino)acetamido)-2-carboxy-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-en-3-yl)methoxy)diazene 1-oxide)-ceftazidime 12, showed higher antibacterial potency than its parent cephalosporin and front-line antipseudomonal antibiotic ceftazidime, good stability against β-lactamases, activity against ceftazidime-resistant P. aeruginosa in vitro biofilms, and efficacy equivalent to ceftazidime in a murine P. aeruginosa respiratory infection model. The results support further evaluation of AMINOPIP2-ceftazidime 12 for P. aeruginosa lung infections in CF and a broader study of "all-in-one" C3Ds for other chronic infections.

Published
2020

35. Walk Through Solar System Times: An Exhibit with an Astrobiology Emphasis

Author

Cheung, C. Y

Subjects
Exobiology
Abstract

In this astrobiology outreach project, we attempt to present the research of the Goddard Center for Astrobiology (GCA) in the context of the history of the Solar System. GCA research emphasizes the origin and formation of complex pre-biotic organic materials in extraterrestrial environments and explores whether the delivery of these primordial materials and water to the early Earth enabled the emergence and evolution of life. The content expounds on areas that are usually not touched upon in a timeline of the Earth's formation. The exhibit addresses the questions: How did our solar system form? How is the formation of our solar systems similar or different from others? How did the organic molecules we observe in space get to the Earth? What conditions are most suitable for life? We will address the issues and challenges of designing the exhibit and of explaining advanced astrobiology research topics to the public.

Published
2012

38. Artificial Intelligence to Detect Papilledema from Ocular Fundus Photographs

Author

MILEA, D., NAJJAR, R. P., ZHUBO, J., TING, D., VASSENEIX, C., Xu, X., AGHSAEI FARD, M., FONSECA, P., VANIKIETI, K., LAGREZE, W. A., LA MORGIA, C., Cheung, C. Y., Hamann, S., Chiquet, C., SANDA, N., Yang, H., MEJICO, L. J., Rougier, Marie-Benedicte, KHO, R., THI HA CHAU, T., Singhal, S., GOHIER, P., CLERMONT-VIGNAL, C., CHENG, C. Y., JONAS, J. B., YU-WAI-MAN, P., FRASER, C. L., Chen, J. J., AMBIKA, S., MILLER, N. R., Liu, Y., NEWMAN, N. J., WONG, T. Y., BIOUSSE, V., Bordeaux population health (BPH), and Université de Bordeaux (UB)-Institut de Santé Publique, d'Épidémiologie et de Développement (ISPED)-Institut National de la Santé et de la Recherche Médicale (INSERM)

Subjects
genetic structures, [SDV.SPEE]Life Sciences [q-bio]/Santé publique et épidémiologie, sense organs, eye diseases, LEHA
Abstract

BackgroundNonophthalmologist physicians do not confidently perform direct ophthalmoscopy. The use of artificial intelligence to detect papilledema and other optic-disk abnormalities from fundus photographs has not been well studied.MethodsWe trained, validated, and externally tested a deep-learning system to classify optic disks as being normal or having papilledema or other abnormalities from 15,846 retrospectively collected ocular fundus photographs that had been obtained with pharmacologic pupillary dilation and various digital cameras in persons from multiple ethnic populations. Of these photographs, 14,341 from 19 sites in 11 countries were used for training and validation, and 1505 photographs from 5 other sites were used for external testing. Performance at classifying the optic-disk appearance was evaluated by calculating the area under the receiver-operating-characteristic curve (AUC), sensitivity, and specificity, as compared with a reference standard of clinical diagnoses by neuro-ophthalmologists.ResultsThe training and validation data sets from 6779 patients included 14,341 photographs: 9156 of normal disks, 2148 of disks with papilledema, and 3037 of disks with other abnormalities. The percentage classified as being normal ranged across sites from 9.8 to 100%; the percentage classified as having papilledema ranged across sites from zero to 59.5%. In the validation set, the system discriminated disks with papilledema from normal disks and disks with nonpapilledema abnormalities with an AUC of 0.99 (95% confidence interval [CI], 0.98 to 0.99) and normal from abnormal disks with an AUC of 0.99 (95% CI, 0.99 to 0.99). In the external-testing data set of 1505 photographs, the system had an AUC for the detection of papilledema of 0.96 (95% CI, 0.95 to 0.97), a sensitivity of 96.4% (95% CI, 93.9 to 98.3), and a specificity of 84.7% (95% CI, 82.3 to 87.1).ConclusionsA deep-learning system using fundus photographs with pharmacologically dilated pupils differentiated among optic disks with papilledema, normal disks, and disks with nonpapilledema abnormalities. (Funded by the Singapore National Medical Research Council and the SingHealth Duke–NUS Ophthalmology and Visual Sciences Academic Clinical Program.)

Published
2020
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44. Metabolic Modeling of the C3-CAM Continuum Revealed the Establishment of a Starch/Sugar-Malate Cycle in CAM Evolution.

Author

Tay, Ignacius Y. Y., Odang, Kristoforus Bryant, and Cheung, C. Y. Maurice

Subjects
CRASSULACEAN acid metabolism, METABOLIC models, WATER efficiency, ELECTRON transport, PLANT metabolism, CORNSTARCH, STARCH
Abstract

The evolution of Crassulacean acid metabolism (CAM) is thought to be along a C3-CAM continuum including multiple variations of CAM such as CAM cycling and CAM idling. Here, we applied large-scale constraint-based modeling to investigate the metabolism and energetics of plants operating in C3, CAM, CAM cycling, and CAM idling. Our modeling results suggested that CAM cycling and CAM idling could be potential evolutionary intermediates in CAM evolution by establishing a starch/sugar-malate cycle. Our model analysis showed that by varying CO2 exchange during the light period, as a proxy of stomatal conductance, there exists a C3-CAM continuum with gradual metabolic changes, supporting the notion that evolution of CAM from C3 could occur solely through incremental changes in metabolic fluxes. Along the C3-CAM continuum, our model predicted changes in metabolic fluxes not only through the starch/sugar-malate cycle that is involved in CAM photosynthetic CO2 fixation but also other metabolic processes including the mitochondrial electron transport chain and the tricarboxylate acid cycle at night. These predictions could guide engineering efforts in introducing CAM into C3 crops for improved water use efficiency. [ABSTRACT FROM AUTHOR]

Published
2021
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45. A multiphase flux balance model reveals flexibility of central carbon metabolism in guard cells of C3 plants.

Author

Tan, X. L. Joshua and Cheung, C. Y. Maurice

Subjects
*CARBON metabolism, *CELL metabolism, *CALVIN cycle, *PENTOSE phosphate pathway, *CELL physiology
Abstract

Summary: Experimental research into guard cell metabolism has revealed the roles of the accumulation of various metabolites in guard cell function, but a comprehensive understanding of their metabolism over the diel cycle is still incomplete due to the limitations of current experimental methods. In this study we constructed a four‐phase flux balance model of guard cell metabolism to investigate the changes in guard cell metabolism over the diel cycle, including the day and night and stomatal opening and closing. Our model predicted metabolic flexibility in guard cells of C3 plants, showing that multiple metabolic processes can contribute to the synthesis and metabolism of malate and sucrose as osmolytes during stomatal opening and closing. Our model showed the possibility of guard cells adapting to varying light availability and sucrose uptake from the apoplast during the day by operating in a mixotrophic mode with a switch between sucrose synthesis via the Calvin–Benson cycle and sucrose degradation via the oxidative pentose phosphate pathway. During stomatal opening, our model predicted an alternative flux mode of the Calvin–Benson cycle with all dephosphorylating steps diverted to diphosphate–fructose‐6‐phosphate 1‐phosphotransferase to produce inorganic pyrophosphate, which is used to pump protons across the tonoplast for the accumulation of osmolytes. An analysis of the energetics of the use of different osmolytes in guard cells showed that malate and Cl− are similarly efficient as the counterion of K+ during stomatal opening. Significance Statement: This work presents a four‐phase metabolic model for predicting guard cell metabolism over the diel cycle. The model predicted an alternative flux mode of the Calvin–Benson cycle that maximises the production of inorganic pyrophosphate during stomatal opening. While multiple metabolic processes were shown to be important in synthesising and metabolising osmolytes in guard cells of different experimental systems, our model demonstrated that these processes can operate simultaneously and at different rates depending on the conditions. [ABSTRACT FROM AUTHOR]

Published
2020
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47. Electron transport process in quantum cascade intersubband semiconductor lasers.

Author

Kalna, K., Cheung, C. Y. L., and Shore, K. A.

Subjects
*ELECTRON transport, *SEMICONDUCTOR lasers, *ELECTRIC fields
Abstract

Detailed self-consistent calculations have been performed of the electron transport and capture aspects of the dynamics of electrically pumped quantum cascade intersubband semiconductor lasers. Specific attention is given to the dependence of the characteristic carrier relaxation times on carrier temperature and density at different applied biases. We have found that the capture and intersubband relaxation times oscillate with increasing electric field. Correlative oscillations can be observed when electron temperature and electron density is plotted as a function of the same applied bias at each energy subband of the laser active region. The temperature and density amplitude are rather less pronounced than those of the relaxations time. Analysis of this typical behavior suggests that the most effective laser structure should work under 70 meV bias. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2001
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48. Self-Consistent Analysis of Carrier--Transport and Carrier--Capture Dynamics in Quantum Cascade Intersubband Semiconductor Lasers

Author

Kalna, K., Cheung, C. Y. L., Pierce, I., and Shore, K. A.

Subjects
Semiconductor lasers -- Research, Business, Computers, Electronics, Electronics and electrical industries
Abstract

A methodology for the self-consistent analysis of carrier transport and carrier capture aspects of the dynamics of quantum cascade intersubband semiconductor lasers is described in this paper. The approach is used to analyze two prototype quantum cascade lasers. The self-consistent analysis incorporates the calculation of the electron densities and temperatures in each subband, together with the intersubband relaxation time. In the calculation of the relaxation time, we take into account the electron interaction with polar optical and acoustic phonons, as well as electron degeneracy. In addition, we also calculate the capture time, considering backward processes that play a role in the electron transition from an injection into an active region. The calculations indicate intersubband relaxation times of order 1 ps and capture times of order 100 fs. Index Terms--Dynamic response, infrared lasers, quantum-well devices, semiconductor heterostructures, semiconductor lasers.

Published
2000

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