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Search Results: 1 - 10 of 1839 matches for " Tran Tuoc "
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Er81 is a downstream target of Pax6 in cortical progenitors
Tran Tuoc, Anastassia Stoykova
BMC Developmental Biology , 2008, DOI: 10.1186/1471-213x-8-23
Abstract: We identified and analyzed the regulatory function of an evolutionarily conserved upstream DNA sequence in the putative mouse Er81 promoter. Three potential Pax6 binding sites were identified in this region. We found that the presence of one of these sites is necessary and sufficient for full activation of the Er81 promoter in Pax6-transfected HeLa cells, while other still unknown factors appear to contribute to Er81 promoter activity in cortical progenitors and neuronal cells. The results suggest that endogenous Pax6, which is expressed at the highest level in progenitors of the rostrolateral cortex, exerts region-specific control of Er81 activity, thus specifying a subpopulation of layer 5 projection neurons.We conclude that the genetic interplay between the transcription factors, Pax6 and Er81, is responsible, in part, for the regional specification of a distinct sublineage of layer 5 projection neurons.In the mammalian neocortex (pallium), neurons with striking morphological and functional diversity are organized radially in six layers, and tangentially into numerous functional domains. Only recently have the molecular and cellular mechanisms that guide the process of corticogenesis responsible for this organization begun to be resolved [1,2]. The main source of cortical projection neurons is the population of pluripotent radial glial progenitors (RG), which divide asymmetrically at the apical surface of the ventricular zone (VZ) and generate both neuronal and glial progeny [3]. After midgestation, RG generate neuronal progenitors, termed intermediate or basal progenitors (BPs), that divide symmetrically at the basal surface of the VZ and in the subventricular zone (SVZ). Thus, while the asymmetric division of RG progenitors gives rise to progeny with distinct cell fates, the symmetric division of BPs primarily modulates the number of cells in previously established neuronal cell lineages [4]. The projection neurons of the lower (6 and 5) and upper (4–2) layers
Layered structures of organic/inorganic hybrid halide perovskites
Tran Doan Huan,Vu Ngoc Tuoc,Nguyen Viet Minh
Physics , 2015,
Abstract: Organic/inorganic hybrid halide perovskites, in which the cations A of an ABX$_3$ perovskite are replaced by organic cations, may be used for solar thermoelectric applications. In this contribution, we systematically study three lead-free hybrid perovskites, i.e., methylammonium tin iodide CH$_3$NH$_3$SnI$_3$, ammonium tin iodide NH$_4$SnI$_3$, and formamidnium tin iodide HC(NH$_2$)$_2$SnI$_3$, by first-principles calculations. We find that in addition to the commonly known motif in which the corner-shared SnI$_6$ octahedra form a three-dimensional network, these materials may also favor a new two-dimensional (layered) motif formed by alternating layers of the SnI$_6$ octahedra and the organic cations. These two motifs are nearly equal in free energy and are separated by low barriers. Interestingly, the layered structures features many flat electronic bands near the band edges, suggested to be interesting for solar thermoelectric applications. These motifs are comparable in terms of the thermoelectric figure of merit $zT$ estimated via a semiclassical model, implying that the interplay of other competing characteristics are crucial. The flat bands revealed for the layered structures may encourage further explorations within the band structure engineering approach for optimizing $zT$.
Low-energy structures of zinc borohydride Zn(BH$_4$)$_2$
Tran Doan Huan,Maximilian Amsler,Vu Ngoc Tuoc,Alexander Willand,Stefan Goedecker
Physics , 2012, DOI: 10.1103/PhysRevB.86.224110
Abstract: We present a systematic study of the low-energy structures of zinc borohydride, a crystalline material proposed for the hydrogen storage purpose. In addition to the previously proposed structures, many new low-energy structures of zinc borohydride are found by utilizing the minima-hopping method. We identify a new dynamically stable structure which belongs to the $I4_122$ space group as the most stable phase of zinc borohydride at low temperatures. A low transition barrier between $I4_122$ and $P1$, the two lowest-lying phases of zinc borohydride is predicted, implying that a coexistence of low-lying phases of zinc borohydride is possible at ambient conditions. An analysis based on the simulated X-ray diffraction pattern reveals that the $I4_122$ structure exhibits the same major features as the experimentally synthesized zinc borohydride samples.
Thermodynamic stability of alkali metal/zinc double-cation borohydrides at low temperatures
Tran Doan Huan,Maximilian Amsler,Riccardo Sabatini,Vu Ngoc Tuoc,Nam Ba Le,Lilia M. Woods,Nicola Marzari,Stefan Goedecker
Physics , 2013, DOI: 10.1103/PhysRevB.88.024108
Abstract: We study the thermodynamic stability at low temperatures of a series of alkali metal/zinc double-cation borohydrides, including LiZn(BH$_4$)$_3$, LiZn$_2$(BH$_4$)$_5$, NaZn(BH$_4$)$_3$, NaZn$_2$(BH$_4$)$_5$, KZn(BH$_4$)$_3$, and KZn$_2$(BH$_4$)$_5$. While LiZn$_2$(BH$_4$)$_5$, NaZn(BH$_4$)$_3$, NaZn$_2$(BH$_4$)$_5$ and KZn(BH$_4$)$_3$ were recently synthesized, LiZn(BH$_4$)$_3$ and KZn$_2$(BH$_4$)$_5$ are hypothetical compounds. Using the minima-hopping method, we discover two new lowest-energy structures for NaZn(BH$_4$)$_3$ and KZn$_2$(BH$_4$)$_5$ which belong to the $C2/c$ and $P2$ space groups, respectively. These structures are predicted to be both thermodynamically stable and dynamically stable, implying that their existence may be possible. On the other hand, the lowest-energy $P1$ structure of LiZn(BH$_4$)$_3$ is predicted to be unstable, suggesting a possible reason elucidating why this compound has not been experimentally identified. In exploring the low-energy structures of these compounds, we find that their energetic ordering is sensitive to the inclusion of the van der Waals interactions. We also find that a proper treatment of these interactions, e.g., as given by a non-local density functional such as vdW-DF2, is necessary to address the stability of the low-energy structures of these compounds.
The Instantaneous Wall Viscosity in Pipe Flow of Power Law Fluids: Case Study for a Theory of Turbulence in Time-Independent Non-Newtonian Fluids
Khanh Tuoc Trinh
Physics , 2009,
Abstract: This paper presents a new theory of turbulence in time-independent non-Newtonian fluids. The wall layer is modelled in terms of unsteady exchange of viscous momentum between the wall and the main stream, following the classic visualisation of inrush-sweep-ejection/burst. The thickness of the wall layer is found to be the same for Newtonian and purely viscous non-Newtonian fluids, when normalised with the instantaneous wall parameters at the onset of bursting. The results indicate that the mechanisms of turbulence in Newtonian and time-independent fluids are identical when structural similarity relations in turbulence are based on phase-locked parameters linked with the development of secondary flows rather than on time-averaged wall parameters. This similarity analysis collapses the local critical instantaneous friction factor data of both Newtonian and non-Newtonian fluids at the point of bursting into a single curve. The method greatly simplifies the analysis of turbulent transport phenomena in non-Newtonian fluids. Keywords: Turbulence, time-independent non-Newtonian, Power law, pipe flow, wall layer
A Four Component Decomposition of the Instantaneous Velocity in Turbulent Flow
Khanh Tuoc Trinh
Physics , 2009,
Abstract: A four component decomposition of the local instantaneous velocity is proposed. It brings out more readily the terms in the Navier-Stokes equations associated with different events and fluid structures of turbulent flows than the classic two component decomposition of Reynolds. In particular the new composition highlights the existence of two types of Reynolds stresses: fast and slow. The fast Reynolds stresses can be linked to a streaming process that describes the ejection of wall fluid in the bursting process. It also provides a simple method for modelling the wall layer. The four components are a long time average, a slow fluctuating component based on the difference between the long term average and the smoothed phase velocity developed by passing coherent structures, a fast fluctuating component which is periodic in nature and a streaming component created by the interaction between the fast fluctuations and the fluid viscous effects. Key words: Velocity components, bursting, streaming flow, smoothed phase velocity, fast and slow Reynolds stresses, wall layer
The Fourth Partial Derivative In Transport Dynamics
Trinh Khanh Tuoc
Physics , 2010,
Abstract: A new fourth partial derivative is introduced for the study of transport dynamics. It is a Lagrangian partial derivative following the path of diffusion, not the path of convection. Use of this derivative decouples the effect of diffusion and convection and simplifies the analysis of transport processes.
A Zonal Similarity Analysis of Velocity Profiles in Wall-Bounded Turbulent Shear Flows
Trinh Khanh Tuoc
Physics , 2010,
Abstract: It is argued that there are three distinct zones in a wall bounded turbulent flow field dominated by three completely different mechanisms: - An outer region where the velocity profile is determined by the pressure distribution - A highly active wall layer dominated by a sequence of inrush-sweep and ejections, and - An intermediate region well described by the traditional logarithmic law proposed by independently Millikan and Prandtl. The log-law and the wall layer are sometimes referred to as the inner region. Under these conditions, a unique set of normalisation parameters cannot possibly apply to all three zones. The inner region can be more successfully represented by normalising the distance and velocity with the values of these scales at the edge of the wall layer since they are shared by both the wall layer and the log-law region. The application of this similarity analysis has successfully collapsed extensive published data for the inner region covering a range of Reynolds numbers from 3000 to 1,000,000 in a variety of geometries including cylindrical pipes, external boundary layers on flat plates, recirculation regions behind a sudden channel expansion, converging rectangular channels and oscillating pipe flows into a unique curve. The normalisation also collapsed drag reducing flow involving ribblets, power law fluids and viscoelastic fluids onto the standard Newtonian curve.
Additive Layers: An Alternate Classification of Flow Regimes
Trinh Khanh Tuoc
Physics , 2010,
Abstract: It is argued that ejections of wall fluid in the bursting process disturb the flow beyond the wall layer and result in the emergence of two new layers in the flow field: the law of the wake and log-law layers. The wall layer represents the extent of penetration of viscous momentum into the main flow and remains constant once it has reached a critical value at the end of the laminar regime. The identification of the three flow regimes: laminar, transition and fully turbulent is conveniently achieved by monitoring the emergence of these three layers
On Virk's asymptote
Trinh Khanh tuoc
Physics , 2010,
Abstract: The Virk asymptote is shown to be similar in nature to the Karman buffer layer profile and does not represent a new log-law with a modified mixing-length. It is simply part of the wall layer velocity profile but is extended because of the increase in wall layer thickness in drag reduction flows. The friction factors at the maximum drag reduction asymptote correspond to velocity profiles consisting of a wall layer and a law of the wake sub-region. Maximum drag reduction results in the suppression of the law of the wake and full relaminarisation of the flow.
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