hoa nguyen - Academia.edu (original) (raw)

Papers by hoa nguyen

PLoS pathogens, 2015

Survival of M. tuberculosis in host macrophages requires the eukaryotic-type protein kinase G, Pk... more Survival of M. tuberculosis in host macrophages requires the eukaryotic-type protein kinase G, PknG, but the underlying mechanism has remained unknown. Here, we show that PknG is an integral component of a novel redox homeostatic system, RHOCS, which includes the ribosomal protein L13 and RenU, a Nudix hydrolase encoded by a gene adjacent to pknG. Studies in M. smegmatis showed that PknG expression is uniquely induced by NADH, which plays a key role in metabolism and redox homeostasis. In vitro, RenU hydrolyses FAD, ADP-ribose and NADH, but not NAD+. Absence of RHOCS activities in vivo causes NADH and FAD accumulation, and increased susceptibility to oxidative stress. We show that PknG phosphorylates L13 and promotes its cytoplasmic association with RenU, and the phosphorylated L13 accelerates the RenU-catalyzed NADH hydrolysis. Importantly, interruption of RHOCS leads to impaired mycobacterial biofilms and reduced survival of M. tuberculosis in macrophages. Thus, RHOCS represents a...

Physical Review B, 2014

ABSTRACT We present a systematic study of the static and dynamic magnetization behavior of interl... more ABSTRACT We present a systematic study of the static and dynamic magnetization behavior of interlayer-coupled mathrmNi80mathrmFe20{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}mathrmNi80mathrmFe20(200 \AA{})/Ru(${t}_{\mathrm{Ru}}$)/${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$(100 \AA{}) trilayers as a function of the Ru spacer layer thickness tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu. As tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu was varied in the range from 0 to 15.8 \AA{}, we observe a strong antiferromagnetic (AFM) exchange coupling between the two ferromagnetic (FM) layers for tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu = 5 \AA{}, which becomes weak for tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu = 10 \AA{}. For tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu = 14.1 \AA{}, the coupled magnetic system changes from AFM to FM ordering. Using broadband ferromagnetic resonance spectroscopy, we have probed the effects of the different coupling mechanisms on both the acoustic and optic magnetic modes. We found that the biquadratic exchange coupling has a negligible effect compared to Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange coupling, while the uniaxial anisotropy at the mathrmNi80mathrmFe20{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}mathrmNi80mathrmFe20/Ru interfaces also plays an important role in determining the behaviors of the modes. A mode anticrossing phenomenon is observed when the RKKY exchange interaction term is above a critical value. A theoretical framework developed is in very good agreement with our experimental results.

The most stable formula for a rational interpolant for use on a finite interval is the barycentri... more The most stable formula for a rational interpolant for use on a finite interval is the barycentric form . A simple choice of the barycentric weights ensures the absence of (unwanted) poles on the real line . In we indicate that a more refined choice of the weights in barycentric rational interpolation can guarantee comonotonicity and coconvexity of the rational interpolant in addition to a polefree region of interest. In this presentation we generalize the above to the multivariate case. We use a product-like form of univariate barycentric rational interpolants and indicate how the location of the poles and the shape of the function can be controlled. This functionality is of importance in the construction of mathematical models that need to express a certain trend, such as in probability distributions, economics, population dynamics, tumor growth models etc.

Numerical Algorithms, 2011

Comonotonicity and coconvexity are well-understood in uniform polynomial approximation and in pie... more Comonotonicity and coconvexity are well-understood in uniform polynomial approximation and in piecewise interpolation. The covariance of a global (Hermite) rational interpolant under certain transformations, such as taking the reciprocal, is well-known, but its comonotonicity and its coconvexity are much less studied. In this paper we show how the barycentric weights in global rational (interval) interpolation can be chosen so as to guarantee the absence of unwanted poles and at the same time deliver comonotone and/or coconvex interpolants. In addition the rational (interval) interpolant is wellsuited to reflect asymptotic behaviour or the like.

Molecular Microbiology, 2010

The MtrAB signal transduction system, which participates in multiple cellular processes related t... more The MtrAB signal transduction system, which participates in multiple cellular processes related to growth and cell wall homeostasis, is the only two-component system known to be essential in Mycobacterium. In a screen for antibiotic resistance determinants in Mycobacterium smegmatis, we identified a multidrugsensitive mutant with a transposon insertion in lpqB, the gene located immediately downstream of mtrA-mtrB. The lpqB mutant exhibited increased cell-cell aggregation and severe defects in surface motility and biofilm growth. lpqB cells displayed hyphal growth and polyploidism, reminiscent of the morphology of Streptomyces, a related group of filamentous Actinobacteria. Heterologous expression of M. tuberculosis LpqB restored wild-type characteristics to the lpqB mutant. LpqB interacts with the extracellular domain of MtrB, and influences MtrA phosphorylation and promoter activity of dnaA, an MtrA-regulated gene that affects cell division. Furthermore, in trans expression of the non-phosphorylated, inactive form of MtrA in wild-type M. smegmatis resulted in phenotypes similar to those of lpqB deletion, whereas expression of the constitutively active form of MtrA restored wild-type characteristics to the lpqB mutant.

Journal of the Korean Physical Society, 2013

ABSTRACT A microscopic theory is employed to study magnonic crystals represented by one-dimension... more ABSTRACT A microscopic theory is employed to study magnonic crystals represented by one-dimensional arrays of ferromagnetic nanorings. The Hamiltonian-based formalism includes the exchange and dipole-dipole coupling within each ring, as well as the long-range dipolar coupling between rings and an external applied magnetic field. Depending on the applied field, the size of the rings, and the inter-ring spacing, the array elements may be in a vortex (flux closure), onion (bidomain), or other inhomogeneous magnetization state. Numerical results are reported for the magnonic bands and gaps in Permalloy nanorings with outer diameter typically of order 100 nm. In a strong-coupling regime it is found typically that the bands are wide and the gaps small in the vortex state, and vice-versa in the onion state.

Journal of Magnetism and Magnetic Materials, 2007

A microscopic Hamiltonian-based method is employed to study the dipole-exchange spin waves in fer... more A microscopic Hamiltonian-based method is employed to study the dipole-exchange spin waves in ferromagnetic stripes and patterned films. The approach allows studies of spin waves in confined geometries, where the magnetization is inhomogeneous, without using phenomenological boundary conditions. Numerical examples are presented for permalloy stripes with an in-plane magnetic field. The spectrum of discrete spin-wave frequencies is obtained, allowing an interpretation of field-dependent spin reorientations and pinning.

Applied Catalysis B: Environmental, 2009

Carbon supported Pd-Ag/C catalyst was prepared using co-reduction method. Physicochemical charact... more Carbon supported Pd-Ag/C catalyst was prepared using co-reduction method. Physicochemical characterization results revealed that alloy nanoparticles with face-centered cubic structure were successfully formed. The electrochemical studies for ethanol oxidation in alkaline media were performed with cyclic voltammetry, linear sweep voltammetry and chronoamperometry methods. The results showed that Pd-Ag/C exhibited an excellent activity, enhanced CO tolerance and better stability than Pt/ C and Pd/C, making it a promising anodic catalyst for alkaline direct ethanol fuel cell. ß

PLoS pathogens, 2015

Survival of M. tuberculosis in host macrophages requires the eukaryotic-type protein kinase G, Pk... more Survival of M. tuberculosis in host macrophages requires the eukaryotic-type protein kinase G, PknG, but the underlying mechanism has remained unknown. Here, we show that PknG is an integral component of a novel redox homeostatic system, RHOCS, which includes the ribosomal protein L13 and RenU, a Nudix hydrolase encoded by a gene adjacent to pknG. Studies in M. smegmatis showed that PknG expression is uniquely induced by NADH, which plays a key role in metabolism and redox homeostasis. In vitro, RenU hydrolyses FAD, ADP-ribose and NADH, but not NAD+. Absence of RHOCS activities in vivo causes NADH and FAD accumulation, and increased susceptibility to oxidative stress. We show that PknG phosphorylates L13 and promotes its cytoplasmic association with RenU, and the phosphorylated L13 accelerates the RenU-catalyzed NADH hydrolysis. Importantly, interruption of RHOCS leads to impaired mycobacterial biofilms and reduced survival of M. tuberculosis in macrophages. Thus, RHOCS represents a...

Physical Review B, 2014

ABSTRACT We present a systematic study of the static and dynamic magnetization behavior of interl... more ABSTRACT We present a systematic study of the static and dynamic magnetization behavior of interlayer-coupled mathrmNi80mathrmFe20{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}mathrmNi80mathrmFe20(200 \AA{})/Ru(${t}_{\mathrm{Ru}}$)/${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$(100 \AA{}) trilayers as a function of the Ru spacer layer thickness tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu. As tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu was varied in the range from 0 to 15.8 \AA{}, we observe a strong antiferromagnetic (AFM) exchange coupling between the two ferromagnetic (FM) layers for tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu = 5 \AA{}, which becomes weak for tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu = 10 \AA{}. For tmathrmRu{t}_{\mathrm{Ru}}tmathrmRu = 14.1 \AA{}, the coupled magnetic system changes from AFM to FM ordering. Using broadband ferromagnetic resonance spectroscopy, we have probed the effects of the different coupling mechanisms on both the acoustic and optic magnetic modes. We found that the biquadratic exchange coupling has a negligible effect compared to Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange coupling, while the uniaxial anisotropy at the mathrmNi80mathrmFe20{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}mathrmNi80mathrmFe20/Ru interfaces also plays an important role in determining the behaviors of the modes. A mode anticrossing phenomenon is observed when the RKKY exchange interaction term is above a critical value. A theoretical framework developed is in very good agreement with our experimental results.

The most stable formula for a rational interpolant for use on a finite interval is the barycentri... more The most stable formula for a rational interpolant for use on a finite interval is the barycentric form . A simple choice of the barycentric weights ensures the absence of (unwanted) poles on the real line . In we indicate that a more refined choice of the weights in barycentric rational interpolation can guarantee comonotonicity and coconvexity of the rational interpolant in addition to a polefree region of interest. In this presentation we generalize the above to the multivariate case. We use a product-like form of univariate barycentric rational interpolants and indicate how the location of the poles and the shape of the function can be controlled. This functionality is of importance in the construction of mathematical models that need to express a certain trend, such as in probability distributions, economics, population dynamics, tumor growth models etc.

Numerical Algorithms, 2011

Comonotonicity and coconvexity are well-understood in uniform polynomial approximation and in pie... more Comonotonicity and coconvexity are well-understood in uniform polynomial approximation and in piecewise interpolation. The covariance of a global (Hermite) rational interpolant under certain transformations, such as taking the reciprocal, is well-known, but its comonotonicity and its coconvexity are much less studied. In this paper we show how the barycentric weights in global rational (interval) interpolation can be chosen so as to guarantee the absence of unwanted poles and at the same time deliver comonotone and/or coconvex interpolants. In addition the rational (interval) interpolant is wellsuited to reflect asymptotic behaviour or the like.

Molecular Microbiology, 2010

The MtrAB signal transduction system, which participates in multiple cellular processes related t... more The MtrAB signal transduction system, which participates in multiple cellular processes related to growth and cell wall homeostasis, is the only two-component system known to be essential in Mycobacterium. In a screen for antibiotic resistance determinants in Mycobacterium smegmatis, we identified a multidrugsensitive mutant with a transposon insertion in lpqB, the gene located immediately downstream of mtrA-mtrB. The lpqB mutant exhibited increased cell-cell aggregation and severe defects in surface motility and biofilm growth. lpqB cells displayed hyphal growth and polyploidism, reminiscent of the morphology of Streptomyces, a related group of filamentous Actinobacteria. Heterologous expression of M. tuberculosis LpqB restored wild-type characteristics to the lpqB mutant. LpqB interacts with the extracellular domain of MtrB, and influences MtrA phosphorylation and promoter activity of dnaA, an MtrA-regulated gene that affects cell division. Furthermore, in trans expression of the non-phosphorylated, inactive form of MtrA in wild-type M. smegmatis resulted in phenotypes similar to those of lpqB deletion, whereas expression of the constitutively active form of MtrA restored wild-type characteristics to the lpqB mutant.

Journal of the Korean Physical Society, 2013

ABSTRACT A microscopic theory is employed to study magnonic crystals represented by one-dimension... more ABSTRACT A microscopic theory is employed to study magnonic crystals represented by one-dimensional arrays of ferromagnetic nanorings. The Hamiltonian-based formalism includes the exchange and dipole-dipole coupling within each ring, as well as the long-range dipolar coupling between rings and an external applied magnetic field. Depending on the applied field, the size of the rings, and the inter-ring spacing, the array elements may be in a vortex (flux closure), onion (bidomain), or other inhomogeneous magnetization state. Numerical results are reported for the magnonic bands and gaps in Permalloy nanorings with outer diameter typically of order 100 nm. In a strong-coupling regime it is found typically that the bands are wide and the gaps small in the vortex state, and vice-versa in the onion state.

Journal of Magnetism and Magnetic Materials, 2007

A microscopic Hamiltonian-based method is employed to study the dipole-exchange spin waves in fer... more A microscopic Hamiltonian-based method is employed to study the dipole-exchange spin waves in ferromagnetic stripes and patterned films. The approach allows studies of spin waves in confined geometries, where the magnetization is inhomogeneous, without using phenomenological boundary conditions. Numerical examples are presented for permalloy stripes with an in-plane magnetic field. The spectrum of discrete spin-wave frequencies is obtained, allowing an interpretation of field-dependent spin reorientations and pinning.

Applied Catalysis B: Environmental, 2009

Carbon supported Pd-Ag/C catalyst was prepared using co-reduction method. Physicochemical charact... more Carbon supported Pd-Ag/C catalyst was prepared using co-reduction method. Physicochemical characterization results revealed that alloy nanoparticles with face-centered cubic structure were successfully formed. The electrochemical studies for ethanol oxidation in alkaline media were performed with cyclic voltammetry, linear sweep voltammetry and chronoamperometry methods. The results showed that Pd-Ag/C exhibited an excellent activity, enhanced CO tolerance and better stability than Pt/ C and Pd/C, making it a promising anodic catalyst for alkaline direct ethanol fuel cell. ß