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Search Results: 1 - 10 of 52166 matches for " James Q Zheng "
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Inhibition of AMPA receptor trafficking at hippocampal synapses by β-amyloid oligomers: the mitochondrial contribution
Yanfang Rui, Jiaping Gu, Kuai Yu, H Criss Hartzell, James Q Zheng
Molecular Brain , 2010, DOI: 10.1186/1756-6606-3-10
Abstract: We found that a brief exposure of hippocampal neurons to Aβ oligomers not only led to marked removal of AMPARs from postsynaptic surface but also impaired rapid AMPAR insertion during chemically-induced synaptic potentiation. We also found that Aβ oligomers exerted acute impairment of fast mitochondrial transport, as well as mitochondrial translocation into dendritic spines in response to repetitive membrane depolarization. Quantitative analyses at the single spine level showed a positive correlation between spine-mitochondria association and the surface accumulation of AMPARs. In particular, we found that spines associated with mitochondria tended to be more resistant to Aβ inhibition on AMPAR trafficking. Finally, we showed that inhibition of GSK3β alleviated Aβ impairment of mitochondrial transport, and effectively abolished Aβ-induced AMPAR loss and inhibition of AMPAR insertion at spines during cLTP.Our findings indicate that mitochondrial association with dendritic spines may play an important role in supporting AMPAR presence on or trafficking to the postsynaptic membrane. Aβ disruption of mitochondrial trafficking could contribute to AMPAR removal and trafficking defects leading to synaptic inhibition.Alzheimer's disease (AD) often attacks aged populations and is highlighted by progressive loss of memory and cognitive abilities [4]. AD brains exhibit two major pathological hallmarks: extracellular senile plaques containing β-amyloid aggregates and intracellular neurofibrillary tangles consisting of hyperphosphorylated microtubule-associated tau proteins [5,6]. β-amyloid (Aβ) molecules are generated by proteolytic cleavage of the transmembrane β-amyloid precursor protein (APP) [7,8]. Aggregated Aβ fibrils constitute the core of neuritic plaques and are believed to be a major culprit for neurodegeneration and subsequent cognitive abnormalities in AD patients [9-11]. Recent studies, however, indicate that Aβ molecules exert adverse effects on neuronal functions
Regulation of chemotropic guidance of nerve growth cones by microRNA
Liang Han, Zhexing Wen, Rachel C Lynn, Marie-Laure Baudet, Christine E Holt, Yukio Sasaki, Gary J Bassell, James Q Zheng
Molecular Brain , 2011, DOI: 10.1186/1756-6606-4-40
Abstract: We found that miR-134 is highly expressed in the neural tube of Xenopus embryos. Fluorescent in situ hybridization also showed that miR-134 is enriched in the growth cones of Xenopus spinal neurons in culture. Importantly, overexpression of miR-134 mimics or antisense inhibitors blocked protein synthesis (PS)-dependent attractive responses of Xenopus growth cones to a gradient of brain-derived neurotrophic factor (BDNF). However, miR-134 mimics or inhibitors had no effect on PS-independent bidirectional responses of Xenopus growth cones to bone morphogenic protein 7 (BMP7). Our data further showed that Xenopus LIM kinase 1 (Xlimk1) mRNA is a potential target of miR-134 regulation.These findings demonstrate a role for miR-134 in translation-dependent guidance of nerve growth cones. Different guidance cues may act through distinct signaling pathways to elicit PS-dependent and -independent mechanisms to steer growth cones in response to a wide array of spatiotemporal cues during development.Developing axons are guided to their specific targets for complex neuronal connections by a spatiotemporal pattern of extracellular cues [1,2]. The motile tip of the axons, the growth cone, reacts to various guidance molecules with distinct responses, including acceleration of extension, inhibition and/or collapse of growth cones, and turning towards or away from attractive or repulsive cues [2,3]. Recent studies have shown that local protein synthesis and degradation play a role in axon guidance [4-9]. However, the mechanisms underlying protein synthesis (PS)-dependent regulation of growth cone guidance remain to be fully elucidated. In addition to the classical translation mechanism involving the mammalian target of rapamycin (mTOR) [6,10,11], increasing evidence indicates that microRNAs (miRNAs), the non-coding RNAs of ~20-23 bps, regulate mRNA expression [12-14]. MiRNAs often bind to target mRNAs through partial complementary pairing to suppress mRNA translation or decrease mRNA
Music in Terms of Science
James Q. Feng
Physics , 2012,
Abstract: To many people, music is a mystery. It is uniquely human, because no other species produces elaborate, well organized sound for no particular reason. It has been part of every known civilization on earth. It has become a very part of man's need to impose his will upon the universe, to bring order out of chaos and to endow his moments of highest awareness with enduring form and substance. It is a form of art dealing with the organization of tones into patterns. Despite of cultural differences, music from different civilizations seems to consist of some building blocks that are universal: melody, harmony, rhythm, etc. Almost all musical systems are based on scales spanning an octave---the note that sounds the same as the one you started off with, but at a higher or lower pitch. It was discovered by Pythagoras, a Greek philosopher who lived around 500 BC, that the note an octave higher than another has a frequency twice high. The notes that sound harmonious together have simple rational number ratios between their frequencies. It is those implicit structures and relationships in apparently mysterious musical experience that I am interested in exploring here. As a scientist by training with a consistent passion for classical guitar playing, I would like make an attempt to explain the musical experience in terms of science and mathematics, hoping to fill some gaps between the knowledge of scientists and artistic intuition of musicians.
Diffusion-Controlled Quasi-Stationary Mass Transfer for an Isolated Spherical Particle in an Unbounded Medium
James Q. Feng
Physics , 2011,
Abstract: A consolidated mathematical formulation of the spherically symmetric mass-transfer problem is presented, with the quasi-stationary approximating equations derived from a perturbation point of view for the leading-order effect. For the diffusion-controlled quasi-stationary process, a mathematically complete set of the exact analytical solutions is obtained in implicit forms to cover the entire parameter range. Furthermore, accurate explicit formulas for the particle radius as a function of time are also constructed semi-empirically for convenience in engineering practice. Both dissolution of a particle in a solvent and growth of it by precipitation in a supersaturated environment are considered in the present work.
Vapor Transport of a Volatile Solvent for a Multicomponent Aerosol Droplet
James Q. Feng
Physics , 2015, DOI: 10.1080/02786826.2015.1072262
Abstract: This work presents analytical formulas derived for evaluating vapor transport of a volatile solvent for an isolated multicomponent droplet in a quiescent environment, based on quasi-steady-state approximation. Among multiple solvent components, only one component is considered to be much more volatile than the rest such that other components are assumed to be nonvolatile remaining unchanged in the droplet during the process of (single-component) volatile solvent evaporation or condensation. For evaporating droplet, the droplet size often initially decreases following the familiar "d^2 law" at an accelerated rate. But toward the end, the rate of droplet size change diminishes due to the presence of nonvolatile cosolvent. Such an acceleration-deceleration reversal behavior is unique for evaporating multicomponent droplet, while the droplet of pure solvent has an accelerated rate of size change all the way through the end. This reversal behavior is also reflected in the droplet surface temperature evolution as "S-shaped" curves. However, a closer mathematical examination of conditions for acceleration-deceleration reversal indicates that the acceleration phase may disappear when the amount of nonvolatile cosolvent is relatively small and ambient vapor pressure is relatively high. Because the net effect of adding nonvolatile cosolvent is to reduce the mole fraction of the volatile solvent such that the saturation vapor pressure is lowered, vapor condensation onto the multicomponent droplet is predicted to occur when the ambient vapor pressure is subsaturated with respect to that for the pure volatile solvent. In this case, the droplet will grow asymptotically toward a finite size. But when the ambient vapor pressure becomes supersaturated with respect to that for the pure volatile solvent, the condensation growth of droplet can continue indefinitely without bound.
The effects of the model errors generated by discretization of "on-off'' processes on VDA
Q. Zheng,M. Mu
Nonlinear Processes in Geophysics (NPG) , 2006,
Abstract: Through an idealized model of a partial differential equation with discontinuous "on-off'' switches in the forcing term, we investigate the effect of the model error generated by the traditional discretization of discontinuous physical "on-off'' processes on the variational data assimilation (VDA) in detail. Meanwhile, the validity of the adjoint approach in the VDA with "on-off'' switches is also examined. The theoretical analyses illustrate that in the analytic case, the gradient of the associated cost function (CF) with respect to an initial condition (IC) exists provided that the IC does not trigger the threshold condition. But in the discrete case, if the on switches (or off switches) in the forward model are straightforwardly assigned the nearest time level after the threshold condition is (or is not) exceeded as the usual treatment, the discrete CF gradients (even the one-sided gradient of CF) with respect to some ICs do not exist due to the model error, which is the difference between the analytic and numerical solutions to the governing equation. Besides, the solution of the corresponding tangent linear model (TLM) obtained by the conventional approach would not be a good first-order linear approximation to the nonlinear perturbation solution of the governing equation. Consequently, the validity of the adjoint approach in VDA with parameterized physical processes could not be guaranteed. Identical twin numerical experiments are conducted to illustrate the influences of these problems on VDA when using adjoint method. The results show that the VDA outcome is quite sensitive to the first guess of the IC, and the minimization processes in the optimization algorithm often fail to converge and poor optimization retrievals would be generated as well. Furthermore, the intermediate interpolation treatment at the switch times of the forward model, which reduces greatly the model error brought by the traditional discretization of "on-off'' processes, is employed in this study to demonstrate that when the "on-off'' switches in governing equations are properly numerically treated, the validity of the adjoint approach in VDA with discontinuous physical "on-off'' processes can still be guaranteed.
Gene expression regulators —MicroRNAs
Fang Chen,James Q. Yin
Chinese Science Bulletin , 2005, DOI: 10.1360/982005-573
Abstract: A large class of non-coding RNAs found in small molecule RNAs are closely associated with the regulation of gene expression, which are called microRNA (miRNA). MiRNAs are coded in intergenic or intronic regions and can be formed into foldback hairpin RNAs. These transcripts are cleaved by Dicer, generating mature miRNAs that can silence their target genes in different modes of action. Now, research on small molecule RNAs has gotten breakthrough advance in biology. To discover miRNA genes and their target genes has become hot topics in RNA research. This review attempts to look back the history of miRNA discovery, to introduce the methods of screening miRNAs, to localize miRNA loci in genome, to seek miRNA target genes and the biological function, and to discuss the working mechanisms of miRNAs. Finally, we will discuss the potential important roles of miRNAs in modulating the genesis, development, growth, and differentiation of organisms. Thus, it can be predicted that a complete understanding of miRNA functions will bring us some new concepts, approaches and strategies for the study of living beings.
An Efficient Parallel VLSI Sorting Architecture
Yanjun Zhang,S. Q. Zheng
VLSI Design , 2000, DOI: 10.1155/2000/14617
Abstract: We present a new parallel sorting algorithm that uses a fixed-size sorter iteratively to sort inputs of arbitrary size. A parallel sorting architecture based on this algorithm is proposed. This architecture consists of three components, linear arrays that support constant-time operations, a multilevel sorting network, and a termination detection tree, all operating concurrently in systolic processing fashion. The structure of this sorting architecture is simple and regular, highly suitable for VLSI realization. Theoretical analysis and experimental data indicate that the performance of this architecture is likely to be excellent in practice.
Left Hand Singularities, Hadron Form Factors and the Properties of the Sigma Meson
Zhiguang Xiao,H. Q. Zheng
Physics , 2000, DOI: 10.1016/S0375-9474(01)01100-9
Abstract: By applying analyticity and single channel unitarity we derive a new formula which is useful to analyze the role of the left-hand singularities in hadron form factors and in the determination of the resonance parameters. Chiral perturbation theory is used to estimate the left-hand cut effects in $\pi\pi$ scattering processes. We find that in the IJ=11 channel the left-hand cut effect is negligible and in the IJ=20 channel the phase shift is dominated by the left-hand cut effect. In the IJ=00 channel the left-hand cut contribution to the phase shift has the wrong sign comparing with the experimental data and therefore it necessitates the $\sigma$ resonance. The new experimental results from the E865 collaboration is crucial in reducing the uncertainty in the determination of the mass and width of the $\sigma$ resonance within our scheme.
Rotating thin-disk galaxies through the eyes of Newton
James Q. Feng,C. F. Gallo
Physics , 2010,
Abstract: By numerically solving the mass distribution in a rotating disk based on Newton's laws of motion and gravitation, we demonstrate that the observed flat rotation curves for most spiral galaxies correspond to exponentially decreasing mass density from galactic center for the most of the part except within the central core and near periphery edge. Hence, we believe the galaxies described with our model are consistent with that seen through the eyes of Newton. Although Newton's laws and Kepler's laws seem to yield the same results when they are applied to the planets in the solar system, they are shown to lead to quite different results when describing the stellar dynamics in disk galaxies. This is because that Keplerian dynamics may be equivalent to Newtonian dynamics for only special circumstances, but not generally for all the cases. Thus, the conclusions drawn from calculations based on Keplerian dynamics are often likely to be erroneous when used to describe rotating disk galaxies.
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