bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Principle Parameters on the Average Stiffness of Optical Tweezer Using Pulsed Gaussian Beams
Authors: Quy Ho Quang , Hai Hoang Dinh , Nam Hoang Van
Published: September 2014

In this article expresions used to simulate the trap stiffness k of the optical trap are derived. The influence of principle parameters as total energy, beam waist and duration of pulsed laser beam, radius of dielectric particle, and viscosity of surrounding medium on the stiffness  is simulated and discussed.
Two Band Model for Diluted Magnetic Semiconductors: Study of the Ferromagnetic Transition Temperature
Authors: Thai Vu Kim , Tuan Hoang Anh
Published: September 2014

The ferromagnetic transition temperature (Tc) of a two band model for diluted magnetic semiconductors (DMS) is calculated by using the coherent potential approximation (CPA). It is shown that Tc is strongly parameter dependent on density of the carriers, magnetic coupling constants, and the hopping terms. The maximal Tc of the two band model is found when both impurity bands fully overlap and this value is approximately twice larger than the highest Tc obtained in the single band model.
Accelerated MD Program Using CUDA Technology
Authors: Hue Hoang Van , Ha Nguyen Thi Thanh , Hung Pham Khac
Published: September 2014

Molecular dynamic (MD) simulation is proven to be an important tool to study the structure as well as the physical properties at atomic level in materials science. However, it requires a huge computing time and hence limits the ability to treat a large scale simulation. In this paper we present a solution to speed up the MD simulation using CUDA technology (Compute Unified Device Architecture). We used the GeForce GTS 250 card with Version 2.30. The simulation is implemented for Lennard-Jones systems with periodic boundary conditions which consist of 1024, 2048, 4096 and 8192 atoms. The calculation shows that the computing time depends on the size of system and could be decreased by 37 times. This result indicates a possibility of constructing a large MD model with up to 105 atoms on the usual PC.
Feasibility Study of Direct Measurement of Stellar Reaction 22Mg(α,p)25Al
Authors: Duy Nguyen Ngoc , Khiem Le Hong
Published: September 2014

The stellar reaction 22Mg(α,p)25Al plays an important role for understanding the nucleosynthesis of stars. It has never investigated yet. We are planning to study this reaction in environment of X-rays burst with temperature T9 = 1÷3 GK using invert kinematics and thick target method. This paper shows a design for direct investigation of this reaction by simulation method. This design is necessary for experimental setup and for confirmation of the feasibility of the experiment.
On the Information Problem of DNA in the Denaturation Process
Authors: Ha My Vi Thi , Huong Vu Thuy , Anh Chu Thuy , Thao To Thi , Thanh Ngo Van , Viet Nguyen Ai
Published: September 2014

The information problem of DNA in the denaturation process was studied by the relationship between entropy and information. Using the previous PBâ€™s (Peyrard and Bishop) numerical results obtained from their microscopic arharmonic model of DNA, we propose a new effective simple model to calculate DNA information. A shape change of information at the denaturation phase transition point was found and discussed.
Density Functional Based Tight Binding Study on Wurzite Core-Shell Nanowires Heterostructures Zno/Zns
Authors: Thuong Nguyen Thi , Minh Nguyen Viet , Tuan Nguyen Ngoc , Tuoc Vu Ngoc
Published: September 2014

We present a Density Functional Based Tight Binding study on the crystallography and electronic structures of various II-VI wurtzite core-shell, core-multi-shell ZnO/ZnS unsaturated nanowires (NW) of circular and hexagonal cross sections and examine the dependence of interface stress and formation energy on nanowire lateral size with diameter range from 20$\mathring{A}$ upto 40$\mathring{A}$. Young's modulus of the wires along the axial growth direction have been estimated. Also the tensile tests have been applied for various wires to show the diameter dependences of their mechanical properties. The electronic properties of these heterostructure nanowires (e.g., Projected Band Structure, Density of State, charge transfer via Mulliken population analysis) also exhibit diameter-dependent behavior.
The Theoretical Magnetization Hysteresis Curve of Nd-Fe-B Anisotropic Bonded Magnets
Authors: Khanh Nguyen Van , Vuong Nguyen Van
Published: September 2014

The theoretical magnetization hysteresis curve of Nd-Fe-B anisotropic bonded magnets is simulated using Jiles-Atherton model and random number generation technique. Gaussian statistics was used to assign magnetic particles to random values of magnetic field (H$_{ai}$) and effective interaction ($\alpha )$ parameters. The prospect of anisotropic bonded magnet is evaluated and discussed.
Polarization Labelling Spectroscopy for NaLi
Authors: Dung Nguyen Tien , Khoa Dinh Xuan , Bang Nguyen Huy , Trong Pham Van
Published: September 2014

We use the polarization labelling spectroscopy technique for simplification of the spectra of alkali-metal NaLi molecule. As a result, the rotational resolution observation for NaLi in the 21 electronic state is reported for the first time.
Leptogenesis in Supersymmetric Economical 3-3-1 Model
Authors: Huong Do Thi , Long Hoang Ngoc , Thuy Nguyen Thi
Published: September 2014

We study a leptogenesis scenario in which the heavy Majorana neutrinos are produced non-thermally in inflaton decays in the supersymmetric economical \(\mathrm{SU}(3)_C\otimes \mathrm{SU}(3)_L \otimes \mathrm{U}(1)_X\) model with inflationary scenario. The lepton-number violating interactions among the inflaton and right-handed neutrinos appear at the one-loop level, and this is a reason for non-thermal leptogenesis scenario. The bound followed from the gravitino abundance and the cosmological constraint on neutrino mass/the neutrino oscillation data is: \(m_{\nu 3} \simeq \frac{0.05}{\delta_{eff}}\) eV. By taking the reheating temperature as low as \(T_R= 10^6\) GeV, we get a limit on the ratio of masses of the light heavies neutrino to those of the inflaton to be: \(\frac{M_{R1}}{M_{\phi}} = 0.87\).
ZnO/CdS Bilayer used for Electrode in Photovoltaic Device
Authors: Chien Dang Tran , Long Pham Duy , Hoi Pham Van
Published: September 2014

In this article we present the fabrication and characterization of the nanoporous ZnO and/or ZnO/CdS thin films onto indium doped-tin oxide (ITO) substrates, based on the thermal evaporation technique followed by thermal treatment. The preparation method was relatively simple and low-cost for large scale uniform coating to produce clean, dense and strong adhesion to substrate thin films. The nanostructured ZnO and ZnO/CdS thin films were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The nanostructured ZnO/CdS bilayer film was used in a photo-electrochemical (PEC) cell as a working electrode and a Pt net as a counter electrode. The results show that the photovoltaic cell with nanostructured ZnO/CdS bilayer film electrode has significantly improved photoelectric capability in comparison with that of ZnO electrode.
Investigation of Energy Transfer in a Blend of electroluminescent Conducting Polymers
Authors: Dinh Nguyen Nang , Nam Nguyen Phuong Hoai , Chung Do Ngoc
Published: September 2014

With the aim of improving the photonic efficiency of an organic light emitting diode a blend of electroluminescent polymers, poly[9-vinylcarbarzole] (PVK) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) was prepared. The energy transfer in the blend was investigated through the comparison of absorption, photoluminescence (PL) and current-voltage (I-V) characteristics of the blend and standard polymers. The obtained results showed that energy transfer from PVK to MEH-PPV enable to form localized excited-state complexes (e.g. exciplexes) in MEH-PPV. The PL intensity of the blended polymers was enhanced as the relative content of MEH-PPV was increased, and particularly, the highest improved PL was observed for an weight fraction of 15 wt{\%} of MEH-PPV in PVK. Organic light emitting diodes made from these blends would exhibit a large photonic efficiency.
Electrodeposition of CuGaSe2 Layer from Solutions with Different Complexing Agents
Authors: Sang Ngo Dinh , Quang Pham Hong , Tu Le Tuan
Published: September 2014

CuGaSe$_{2}$ (CGS) thin films were deposited on ITO substrates by electrodeposition from the solutions with different acidic agents, namely hydrochloric, sulphamic and citric acids. Cyclic voltammetry (CV) studies of unitary Cu, Ga, and Se systems and ternary Cu-Ga-Se systems were carried out to determine the reduction potentials, the mechanism of deposition and the ability to deposit of each constituent. The reduction peaks were observed in all unitary systems except the case of Ga from solution with non-acid and citric acid. For the ternary systems, the voltammograms only show the peaks relating to the reduction of Cu$^{2 + }$ and Se$^{4 + }$, indicating the difficulty in deposition of Ga. The electrodepositions have been processed at - 0.6 V and - 0.95 V vs. SCE. The concentration of the films was determined by EDS. For all complexing agents, the concentration of Ga has been found to depend strongly on the deposition potential and has reached to the value of about 16{\%} at. at potential of -0.95 V from the solutions with hydrochloric and sulphamic acids.
Random Lasing from a Layer of ZnO Powder Painted on Glass Substrate under Excitation of Nanosecond and Picosecond Laser Pulses
Authors: Binh Nguyen The , Thin Pham Van , Nga Pham Thu , Tuan Nguyen Anh
Published: September 2014

The ZnO powder which consists of monodisperse colloidal spheres with average diameter of 100-300 nm was synthesized by hydrolysis of Zinc acetate dehydrate. The random lasing around 380 nm was produced from a layer of the ZnO powder painted on a glass substrate and optically pumped at 355 nm. Our experimental results show that random laser action of a layer of ZnO spherical nanoparticles and the characteristics of these random lasers under excitation of nanosecond and picosecond laser pulses.
Synthesis of Gold Nanoparticles Conjugated with Protein A: Towards the Application in Biosensors for Virus Detection
Authors: Huy Tran Quang , Tuan Mai Anh
Published: September 2014

In this article, a facile and effective technique is described to prepare a complex of gold nanoparticles (GNPs)/protein A (PrA) for biosensors in virus detection. GNPs were synthesized by the reduction of tetrachloroauric (III) acid trihydrate using sodium ascorbate, and then coated with PrA via ultracentrifugation. The complex of GNPs/PrA was characterized using UV-vis spectroscopy and transmission electron microscopy. The immunogold labeling method of scanning electron microscopy was also used to verify the capacity for the detection and binding of GNPs/PrA to H$_{1}$N$_{1}$ influenza A virus particles. The results showed that GNPs were spherical, uniform shape, and approximately 10 nm in size. Noticeably, the complex of GNPs/PrA could detect and bind effectively to H$_{1}$N$_{1}$ influenza A virus particles by a large number of GNPs surrounded. The advantage of the complex of GNPs/PrA showed a highly potential application in biosensors with the improvement of the sensitivity and transducing signal for virus detection.
Study on Lattice and Electronic Structures at the Surface of BaTiO3 Thin Films by DFT Method
Authors: Chinh Nguyen Van , Cong Bach Thanh , Linh Nguyen Hoang
Published: September 2014

In this paper, the density functional theory (DFT) study on nano-thin films of the most typical ferroelectric compound BaTiO$_3$ was presented. The results showed that the convergence of the film model using for DFT calculation were obtained for the thickness of the vacuum slabs as large as ten times of the BaTiO$_3$ slabs within the total energy error $\bsim$ 0.01 eV. The lattice contraction was observed in the surface region of the material. The difference in atomic layer termination, between BaO terminated and TiO$_2$ terminated films, gives rise to the difference in lattice reconstruction at the surface region which, in turn, leads to the difference in surface electric dipoles. The surface effect acts on the electronic structure of thin films in the manner of the asymmetry of atomic sites and the structural reconstruction due to the surface relaxation. Our results indicated that the termination also decides how and how much these two manners take effects on the electronic structure of the material.
Electron Mobility in an Unintentionally Doped GaN/AlGaN Surface Quantum Well
Authors: Minh Nguyen Viet
Published: September 2014

We present a theoretical study the two-dimensional electron gas 2DEG at low temperature in an unintentionally doped GaN/AlGaN surface quantum well, taking adequate account of the roughness-induced scattering mechansms and effect due to sheet polarization charges.  Within model of surface quantum wells 2DEG be described by an extended Fang-Howard wave function, we are able to derive an analytic expression for the self-consistent Hartree potential. Thus, we obtained simple expresion describing the enhancement of the 2DEG screening and unscreened\break potentials for different scattering sources. We studied the electron mobility due to different scattering sources and the total electron mobility in an unintentionally doped GaN/AlGaN surface quantum well.
Effect of the direct exchange interaction between magnetic impurities on magnetization in diluted magnetic semiconductors
Authors: Thai Vu Kim , Anh Le Duc , Tuan Hoang Anh
Published: September 2014

We consider a model of III-V diluted magnetic semiconductors where both of the exchange interaction between carrier and impurity spins, and the direct exchange interaction between magnetic impurities are taken into account. The magnetization as a function of temperature for a wide range of model parameters is calculated and discussed. We show that for a degenerate carrier system the suppression of the magnetization is sensitive to the antiferromagnetic coupling constant and the impurity concentration.
Renormalization Group and 3-3-1 Model with the DiscreteFlavour Symmetries
Authors: Long Hoang Ngoc , Ngan Nguyen Thi Kim
Published: September 2014

Renormalization group equations of the 3-3-1 models with A4 and S4 flavor symmetries as the only intermediate gauge group between the standard model and the scale of unification of the three coupling constants are presented. We shall assume that there is no necessarily a group of grand unification at the scale of convergence of the couplings.
Evolution of Protein-protein Interaction Networks in Duplication-Divergence Model
Authors: Thuy Bui Phuong , Hoang Trinh Xuan
Published: September 2014

Protein interacts with one another resulting in complex functions in living organisms. Like many other real-world networks, the networks of protein-protein interactions possess a certain degree of ordering, such as the scale-free property. The latter means that the probability $P$ to find a protein that interacts with $k$ other proteins follows a power law, $P(k) \sim k^{-\gamma}$. Protein interaction networks (PINs) have been studied by using a stochastic model, the duplication-divergence model, which is based on mechanisms of gene duplication and divergence during evolution. In this work, we show that this model can be used to fit experimental data on the PIN of yeast Saccharomyces cerevisae at two different time instances simultaneously. Our study shows that the evolution of PIN given by model is consistent with growing experimental data over time, and that the scale-free property of protein interaction network is robust against random deletion of interactions.
Phase Structure of Linear Sigma Model without Neutrality Constraint (I)
Authors: Phat Tran Huu , Thu Nguyen Van
Published: September 2014

The pion condensation and chiral phase transition are studied within the linear sigma model with constituent quarks (LSMq). In the chiral limit the pion condensation is always the first-order phase transition and the phase diagrams of the pion condensate are established respectively in the \((\mu,T) , (\mu_I,T)\) and \((\mu_I,\mu)\)-planes, here \(T, \mu\) and \(\mu_I\) are temperature, baryon chemical and isospin chemical potentials. In the physical world, where the chiral symmetry is explicitly broken we investigate systematically the phase structure of pion and chiral condensates in the \((T-\mu-\mu_I)\)-space. The obtained results are mainly compared to the existing data derived from the lattice QCD (LQCD) and the Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model.
Temperature Effects on the Plasmon Modes of Double-layer Graphene
Authors: Tuan Dinh Van , Khanh Nguyen Quoc
Published: September 2014

We calculate the dynamical dielectric function of doped double-layer graphene (DLG), made of two parallel graphene monolayers with carrier densities \(n_1, n_2\), respectively, and a separation interlayer of \(d\) at finite temperature. The results are used to find the dispersion of plasmon modes. We study the temperature effects on the DLG plasmon modes in the case of symmetric system \((n_1=n_2)\), asymmetric system \((n_1\neq n_2)\) and no free carriers in the second layer \((n_2=0)\). We show that the effect of temperature on the plasmon dispersion is significant and can not be ignored in investigating graphene properties.
Optical Properties of \(\text{CuInS}_{2}\) Thin Films Prepared by Spray Pyrolysis
Authors: Thai Tran Thanh , Hung Pham Phi , Son Vo Thach , Bich Vu Thi
Published: September 2014

Polycrystalline CuInS\(_{2}\) (CIS) absorber films for solar cells were prepared by spray pyrolysis of aqueuos solution of copper chloride, indium chloride and thiourea onto heated glass substrates. By optimizing the spray parameters, such as reducing/increasing the temperature of the substrate and molar ratio of Cu/In in the spraying solution, the optical characteristics of films, which are well matched to the solar spectrum, were identified. In all cases, those CIS thin films were of p-type conductivity. Transmission measurements were performed to examine the optical properties of the films; the absorption coefficient and the optical band gap of the films were calculated by transmission spectra. The absorption spectra of the films showed that this compound is a direct band gap one and its gap varied between 1.30 - 1.78 eV. Those thin films were analyzed by X-ray diffraction in order to understand the effect of layers structure on their optical properties.
Phase structure of linear sigma model with neutrality constraint (II)
Authors: Phat Tran Huu , Thu Nguyen Van
Published: September 2014

The phase structure of the linear sigma model with constituent quarks and the electric neutrality is systematically studied in the mean field theory. It results that in the chiral limit, as function of $T$ and chemical potential \\(\mu\\), the pion condensate undergoes a first-order phase transition. In the physical world, the phase diagram of chiral condensate exhibits a first-order phase transition, which ends at a critical end point (CEP) for $\alpha < 0.3$, where $\alpha$ is the fraction of $\pi^+$  contribution to the condensate.
Precision Frequency Measurement for He-Ne/ I2 Laser Emission with kHz- Accuracy
Authors: Thang Le Huu , Thu Bui Quoc , Xuan Vu Khanh , Suh Ho Suhng , Hoi Pham Van
Published: September 2014

An accurate and precise frequency measurement of S.I. unit traceability is essential not only in the field of frequency metrology but also in many fundamental scientific researches, because an accurate and precise frequency will be able to provide stable reference frequency related quantities like length and time -- the two important elements of physics. In this paper we present our frequency measurement for laser emission of the He-Ne/I2 laser system at the kHz accuracy and precision level. A frequency beat measurement of the laser under test with the standard frequency from a frequency optical comb is conducted. The second measurement method based on the heterodyne technique, where the beats between the hyperfine frequencies of 127I2 isotope at frequency of 474 THz and the testing He-Ne laser frequency recorded. The measurement data from different measurement techniques show a good consistency and therefore the given data are reliable.
The Simulation of the Stabilizing Process of Glass Nanoparticle in Optical Tweezer Using Series of Laser Pulses
Authors: Quy Ho Quang , Hai Hoang Dinh
Published: September 2014

In this article the stable region and stabilizing process of dielectric particle in fluid by the optical tweezer using the series of laser pulses are investigated. The influence of the repetition period and number of laser pulses on the radial variance of particle and the ``so-called'' stable space-time pillar is simulated and discussed.
Curie Temperature of Diluted Magnetic Semiconductors: the Influence of the Antiferromagnetic Exchange Interaction
Authors: Tuan Hoang Anh , Thai Vu Kim , Anh Le Duc
Published: September 2014

The coherent potential approximation and mean field approximation are used to calculate the free energy of the coupled carrier – localized spin system in III-V diluted magnetic semiconductors. Thus the magnetic transition temperature Tc can be determined and its dependence on important model parameters. We show that the strong antiferromagnetic superexchange interaction between nearest neighbour sites considerably reduces the Curie temperature.
Photon - Axion Conversion Cross-Sections in a Resonant Cavity with general mode
Authors: Thuy Dao Thi Le , Thuc Le Nhu
Published: September 2014

Photon-axion conversions in the resonant cavity with the general mode (TM$_{mn0}$) are considered in detail by the Feynman diagram method. The differential cross-sections are presented and numerical evaluations are given. It is shown that there is a resonant conversion for the considered process, in which the conversion cross-sections are much larger than those of the wave guide in the same conditions. Some estimates for experimental conditions are give from our results.
Effect of Oxygen Pressure on Transport Propeties of Al-doped ZnO Films Grown by PED
Authors: Sang Ngo Dinh , Quang Pham Hong , Ngoc Do Quang
Published: September 2014

Al-doped ZnO films were grown by pulsed electron deposition (PED) at room temperature and 400 oC and at the oxygen pressure ranged from 3 mTorr to 20 mTorr. Transport properties were measured by van der Pauw technique. Crystallinity of the films was characterized by X-ray diffraction. It was found that the films grown at room temperature have a very high resistivity due to poor crystallinity. For the films grown at 400 o C, the obtained results indicate that the film grown at a lower pressure has a higher carrier mobility as well as a higher carrier concentration, resulting in a lower resistivity. This phenomenon has been discussed in term of the concentration of oxygen vacancies and the number of traps for carriers.
Investigation of GAS Gain of GEM-Foil Used in Low Energy Radioactive Beam Experiments
Authors: Duy Nguyen Ngoc , Khiem Le Hong
Published: September 2014

Study of nuclear reactions using radioactive beams at low energy plays an important role in nuclear astrophysics and nuclear structure. The trajectory of particle beams can be obtained by using an active gas target, multiple-sampling and tracking proportional chamber (MSTPC). Because of low intensity of radioactive beam when studying the stellar nuclear reactions such as (α, p), (p, α),… it is necessary to increase the gain of the tracking counter system. A Gas Electron Multiplier (GEM) foil and the proportional counter called as GEM-MSTPC have been used for this purpose. In this study, the dependence of the effective gas gain of GEM foils on the foil thickness and on the operating pressure was investigated. Two types of GEM foil with the thickness of 400 μm and 200 μm in Argon (70%) – Carbon dioxide (30%) mixture have been used. This investigation is important for our direct measurement of 22Mg(α, p) reaction, which is planed to perform in 2012 at RIKEN.
Octonionic Extension of \(U(1) \times SU(2)\) Gauge Analyticity of Dyons
Authors: Bisht Praveen Singh , Dangwal Shalini , Negi O. P. S.
Published: September 2014

Starting with the generalized electromagnetic (and gravi-magnetic) fields of dyons (and grvito-dyons), the octonion generalization of \(U(1)\times SU(2)\) gauge theories of dyons (and grvito-dyons) has been developed in a consistent way. The resemblance between octonion covariant derivative and the gauge covariant derivative has also been established . Expressing the generalized four - potential, current and fields of dyons (and gravito - dyons) in terms of split octonion variables, we have discussed the consistent forms of \(U(1)\) abelian and \(SU(2)\) non - Abelian gauge theories for dyons (and gravito - dyons). It is shown that the present formalism reproduces the theory of electric (gravitational) charge (mass) in the absence of magnetic (Heavisidean) charge (mass) on dyons (gravito - dyons) or vice versa.
Optical pulse Self-compressor combined the Nonlinear coupler with Backward Raman fiber amplifier
Authors: Bien Chu Van , Quy Ho Quang , Lanh Chu Van , Luu Mai Van , Thanh Thai Doan
Published: September 2014

Based on the nonlinearity of the nonlinear optical coupler (NOC) and the amplifying capacity of the backward Raman fiber amplifier (PBRFA), a new optical system to compress the optical pulse (optical pulse self-compressor: OPSC) is proposed. Using the expressions describing relationship between output intensities from both output ports and input one of NOC and the expression describing the amplification of the PBRFA, the compressing process of the optical pulse propagating through OPSC is simulated. The results show that the peak of optical pulse will be enhanced and the duration of optical pulse will be reduced significantly, and the shape of input pulse is completely compressed with certain efficiency. It means the optical pulse is self-compressed without the pump pulse.
Mott Transitions in the 2-band Hubbard Model: A Coherent Potential Approximation Study
Authors: Anh Le Duc , Tuan Hoang Anh
Published: September 2014

The half-filled isotropic degenerate two-band Hubbard model is studied within coherent potential approximation. The model is characterized by an Ising-type Hund’s exchange coupling, intra- and inter-orbital Coulomb parameters. We found that the band degeneracy slightly reduces the Mott-Hubbard critical value \(U_C\). We reveal that the system can have two distinct critical values for Mott-Hubbard transitions.
Prototyping of DSSDs for Particle Tracking and Spectroscopy within the EXL Project at Fair
Authors: Chung Le Xuan , Egelhof P. , Ilieva S. , Streicher B. , Borger R. , Rigollet C. , Kalantar-Nayestanaki N. , Najafi A. , Davinson T. , Woods P. J. , Eremin V. , Mutterer M. , Von Schmid M. , Khai Nguyen Tuan
Published: September 2014

Prototype double-sided silicon strip detectors (DSSD\(s\)) of 300 \(\mu \)m thickness produced at PTI St. Petersburg (Russia) were tested for the use as position sensitive, \(\Delta E\) and E detectors for tracking and particle identification in the EXL (EXotic nuclei studied in Light-ion induced reactions at the NESR storage ring) setup at the FAIR (Facility for Antiproton and Ion Research) project at GSI. We describe the characteristics of detectors with \(16 \times 16,\;64\times 64\) and \(64\times 16\) strips, respectively. The response of these detectors for \(^{241}\)Am \(\alpha\) particles injected either from the p or n side was examined. The test measurements were performed partially at GSI and the University of Edinburgh. A first in-beam test with a proton beam of 50 MeV with the latter two DSSDs and two 6.5 mm thick Si(Li) detectors was also done at KVI Groningen, the Netherlands. The results reveal good spectroscopic properties of these detectors.
Electron Distribution in AlGaN/GaN Modulation-doped Heterostructures
Authors: Thao Dinh Nhu , Tien Nguyen Thanh
Published: September 2014

We present a calculation of the distribution of two-dimensional electron gas (2DEG)along the quantization direction in an AlGaN/GaN modulation-doped heterostructure (MDHS).The main conﬁnement sources from ionized donors, 2DEG and polarization charges are prop-erly taken into account. We show that the 2DEG distribution near the MDHS interface dependsstrongly on the model of potential barrier in use. Within the ideal model of inﬁnite potential bar-rier, the 2DEG distribution near the interface is increased with a rise of the sheet densities of2DEG and polarization charges. On the contrary, this distribution is decreased within the realisticmodel of ﬁnite potential barrier. Since the key mechanisms limiting the 2DEG mobility in MDHSare alloy disorder and surface roughness scatterings that are very sensitive to the near-interface2DEG distribution, with a rise of the sheet densities of 2DEG and polarization charges the 2DEGmobility is decreased within the inﬁnite-barrier model, while increased within the ﬁnite one.
Optimization of Trio-Cavity Raman Laser Pumped by Pulsed Gaussian Beam
Authors: Khoa Dinh Xuan , Lanh Chu Van
Published: September 2014

In the paper the set of dimensionless rate equations for the pump, Stokes and anti-Stokes powers in the trio-cavity Raman laser pumped by pulsed Gaussian beam is introduced. By numerical Runger-Kuta method, those equations are resolved and the optimal normalized parameters for enhance the output powers are found out.
Organic - Inorganic Hybrid Luminescent Composite for Solid-state Lighting
Authors: Chung Do Ngoc , Tuan Le Trac , Hao Tran Cong , Hieu Do Ngoc , Dinh Nguyen Nang , Duong Pham Hong
Published: September 2014

White light emitting diodes (WLEDs) made by coating organic and inorganic hybrid composites on blue LED chips. Y3Al5O12:Ce (YAG:Ce) nano inorganic powder prepared by low-temperature Sol-Gel method exhibited broad green emission with the peak at 521 nm. Poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) polymer has high luminescence efficiency and red emission peak at 590 nm. The white light was obtained by mixing blue light from emission of the blue LED chip - Indium Gallium Nitride (InGaN) and green-red light from the fluorescence of nano- YAG:Ce and MEH-PPV polymer hybrid composite. The hybrid nanocomposite-based WLEDs exhibited broad band emission spectra from blue light to red wavelengths and provided the white light with a CIE-1931 coordinate of x = 0.2986, y = 0.2620 and a colour rendering index Ra = 84.36. The results suggest a potential application of nanocomposite based WLEDs in efficient solid-state lighting.
Determination of Wavelength Shift of Fiber Bragg Grating Sensors by Tunable Single-mode Diode Laser
Authors: Anh Nguyen The , Son Pham Thanh , Van Nguyen Thuy , Cam Hoang Thi Hong , Minh Ngo Quang , Huy Bui , Hoi Pham Van
Published: September 2014

We propose a novel principle of determination of fiber Bragg grating (FBG) wavelength shift which is impacted by a variation of physical parameters such as temperature, pressure and/or strain. In common case the wavelength shift of FBG was monitored by wavelength measurement using a high-cost spectrometer and a broad band light source. In our proposed technique the wavelength shift of FBG can be determined by change of lasing wavelength of distributed feedback laser (DFB-laser) due to the change of laser substrate temperature. The maximal opto-electrical intensity of photodetector would be obtained when the laser wavelength and FBG reflection wavelength are coincided. The FBG sensor prototype has shown excellent response for laser temperature change in the range of \(10^{\circ}C-50^{\circ}C\) with the ratio \(\Delta \lambda /\Delta T\) of the DFB laser is of 77.5 pm.K\(^{ - 1}\). Key features of the proposed technique are fabrication of low-cost FBG sensors for civil engineering.
The Influence of the Self-focusing Effect on the Optical Force Acting on Dielectric Particle Embedded in Kerr Medium
Authors: Nam Hoang Van , Le Cao Thanh , Quy Ho Quang
Published: September 2014

The influence of the self-focusing effect arised from Kerr effect on the optical force acting on the dielecric particle embedded in the Kerr medium, which is irradiated by the Gaussian beam, is proposed to concern. The expressions of the optical forces with the nonlinear refractive index and nonlinear focal length are derived. Using them, the distribution of the optical forces in the trapping region of the optical tweezer is simulated and discussed for same distinguished case of the Kerr medium with different nonlinear coefficients. The results show that the stabe region of the optical tweezer depends on the nonlinear coefficient of refractive index. Moreover, the stable region could be brokendown with a critical value of the nonlinear coefficient of refractive index of the surrounding medium irradiated by Gaussian laser pulse described by given parameters as  intensity, duration and radius of beam waist.
Molecular Constants of the 2\(^1\Pi\) State of \(\text{NaLi}\) Molecule
Authors: Dung Nguyen Tien , Trung Le Canh , Khoa Dinh Xuan , Bang Nguyen Huy
Published: September 2014

We report our determination of molecular constants for the 21Π state of NaLi from set of 732 spectral lines. Using the linear least-squares fitting method, an optimum set of molecular constants, which corresponds to dimensionless root mean of squares of deviation σ = 0.62 within 0.1 cm-1 experimental uncertainty, have been derived.
Influence of the Frequency-chirp on Pulse in Passively Mode-locking Optical Fiber Ring Laser
Authors: Kien Bui Xuan , Hung Tran Hai , Chien Trinh Dinh
Published: September 2014

We consider a model of a passively mode-locking fiber ring laser bult using a saturable absorber and a chirped fiber Bragg grating to balance dispersion and nonlinearity. The evolution of the slowly envelope of the optical field in a loop fiber subject to dispersion , Kerr nonlinearity, frequency- chirp and nonlinear absorption is given by the generalized complex Ginzburg-Landau equation. The influence of the frequency-chirp on the pulse is simulated and discussed, and the stationary conditions concerning the chirp parameter are  found out for our laser.
Study on the Phase Transition Behavior of Fishes Schooling System
Authors: The Nguyen Phuoc , Sang-Hee Lee , Thanh Ngo Van , Viet Nguyen Ai
Published: September 2014

The Vicsek’s model (VM) [T. Vicsek, et. al., Phys. Rev. Lett. 75, 1226 (1995)] is apopular approach to study nature of the phase transition of self-propelling system. In this model,the direction of motion of each particle depends on the average velocity of its neighboring particleswithin a circle of radius R. In this work, we consider a group of ﬁshes as the particles, but weassumed that only the individuals of its neighbors within a circle sector with central angle ϕ (iscalled angle of view) and radius R, are taken into account the average direction of motion. Weused a similar model as the well known XY spin model on a square lattice of linear size L, theparticles can move freely on the plane (an oﬀ-lattice model). A phase diagram in the space (φ,ξc) has been established where φ = ϕ/2 2 [0, π] and ξc being the critical noise. We shown thatξc strongly depends on the view’s angle φ 0.5π, but slightly varies with φ < 0.5π. So, we canconclude that the schooling behavior of animal is only of the prey species, but not of the predator
Lowest Excited-State Impurity Binding Energy in InGaN/GaN Parabolic QWW: Magnetic Field Effect
Authors: El Ghazi Haddou , Jorio Anouar , Zorkani Izeddine
Published: September 2014

In this paper, we have investigated the magnetic field effect on the lowest excited-state binding energy of hydrogenic shallow-donor impurity in wurtzite (In,Ga)N/GaN parabolic transversal-section quantum-well wire (PQWW) using the finite-difference method within the quasi-one-dimensional effective potential model. The calculations are performed within the framework of the effective mass approximation. A cylindrical QWW effective radius is taken into account to describe the lateral confinement strength. The numerical results show that: (i) the probability density is the largest on a circularity whose radius is the effective radius and (ii) the lowest excited-state binding energy is the largest when an impurity is located on this circularity while it starts to decrease as the impurity is away from the circularity.
Response of Water Cherenkov Detectors to Small Signals: a Case Study
Authors: Thao Nguyen Thi , Diep Pham Ngoc , Dong Pham Ngoc , Nhung Pham Thi Tuyet , Darriulat Pierre , Anh Pham Tuan , Hoai Do Thi
Published: September 2014

Detailed studies of the response of the VATLY water Cherenkovdetector, a replica of those used in the ground array of the PierreAuger Observatory, are presented with emphasis on the response to lowamplitude signals. The method used is to detect decay electrons frommuons stopping in the water volume. Results include properties of the detection process as well as of the atmospheric cosmic ray flux.
Effects of ribosomal exit tunnel on protein's cotranslational folding
Authors: Thuy Bui Phuong , Hoang Trinh Xuan
Published: September 2014

In vivo, folding of many proteins occurs during their synthesis in the ribosomeand continues after they have escaped from the ribosomal exit tunnel. Inthis research, we investigate the confinement effects of the ribosome on thecotranslational folding of three proteins, of PDB codes 1PGA, 1CRN and 2RJX,by using a coarse-grained model and molecular dynamics simulation. The exittunnel is modeled as a hollow cylinder attached to a flat wall, whereas aGo-like model is adopted for the proteins. Our results show that theexit tunnel has a strong effect on the folding mechanism by setting an order bywhich the secondary and tertiary structures are formed. For protein 1PGA, thefolding follows two different folding routes. The presence of the tunnel alsoimproves the foldability of protein.
Re-examination of Two Zero Texture of Neutrino Mass Matrix After Neutrino-2012
Authors: Phong Nguyen Thanh
Published: September 2014

We re-study the seven neutrino mass matrices with two independent vanishing entries under the latest results of neutrino oscillation experiments after the neutrino - 2012 conference. It is shown that the pattern B 1 could be excluded since this pattern realizes very small value of mixing angle theta13. The remain six textures satisfy the current experimental data. We also find that all seven textures of neutrino mass matrix possess the normal hierarchy of neutrino mass spectrum.
Vacuum Stability in Supersymmetric Reduced Minimal 3-3-1 Model
Authors: Thao Nguyen Huy , Phuong Ly Thi Mai , Hue Le Tho
Published: September 2014

We investigate the vacuum stability conditions of theSupersymmetric reduced minimal 331 model (SUSYRM331) that createimportant  consequences on  Higgs mass spectrum as well assoft-parameters of the model. We prove that if this condition issatisfied then all Higgses are massive. Furthermore,soft-parameters should be in order of \(SU(3)_L\) scale. Based onthis, we investigate in detail masses of CP-even neutral  anddoubly charged Higgses in the model. The  neutral Higgs sectorincludes one light Higgs with mass at tree level \(m_{H^0_1}\simeq m_Z|\cos 2\gamma | < 92.0\) GeV and three other heavy Higgses. Fordoubly charged Higgses, there may exist a light Higgs which can beobserved by recent colliders such as LHC.
Influence of Spin Fluctuation on the Magnetic Properties of EuO Ultra-thin Film
Authors: Thao Pham Huong , Cong Bach Thanh
Published: September 2014

The Gaussian spin fluctuation theory is applied to study magnetic properties (Curie temperature, magnetization) of EuO  ultra-thin films within nearest neighbor and next nearest neighbor exchange approximation. The dependence of Curie temperature on the thickness of the free EuO ultrathin film is calculated and compared with the results of the other mean field method- constant coupling approximation. The effect of nearly independence of saturation magnetization on the EuO films thickness measured  in [8] can be explained by controlling the next nearest neighbor exchange in presence of substrates.
Folding Model Study of the Elastic Alpha-alpha Scattering at Low Energies
Authors: Tan Ngo Ha , Phuc Nguyen Hoang , Khoa Dao Tien
Published: September 2014

The folding model analysis of the elastic \(\alpha + \alpha\) scattering at the incident energies below the reaction threshold of 34.7 MeV (in the lab system) has been done using the well-tested density dependent versions of the M3Y interaction and realistic choices for the \(^4\)He density. Because the absorption is negligible at the energies below the reaction threshold, we were able to probe the \(\alpha + \alpha\) optical potential at low energies quite unambiguously and found that the α + α overlap density used to construct the density dependence of the M3Y interaction is strongly distorted by the Pauli blocking. This result gives possible explanation of a long-standing inconsistency of the double-folding model in its study of the elastic \(\alpha + \alpha\) and \(\alpha\)-nucleus scattering at low energies using the same realistic density dependent M3Y interaction.
Towards Design of High Spin Metal-free Materials
Authors: Thanh Nguyen Van , Tuan Nguyen Anh
Published: September 2014

In this paper, in order to explore high-spin carbon-based magnetic materials with strong ferromagnetic coupling, geometric structure, electronic structure and magnetic properties of alternating stacks of \(\pi \)-radical-halogenated-hydrocarbons and diamagnetic molecules have been investigated based on density-functional theory with dispersion correction. These alternating stacks are predicted to avoid the typical antiferromagnetic spin-exchange of indentical face-to-face radicals via spin polarization of a diamagnetic molecule in between. Our results show that \(\pi\)-radical-halogenated-hydrocarbons like perchlorophenalenyl (C\(_{13}\)Cl\(_{9})\) is strong ferromagnetic coupling if alternatingly stacked with aromatics like fluorinated coronene (C\(_{24}\)F\(_{12})\) or coronene (C\(_{24}\)H\(_{12})\), while fluorinated perinaphthenyl (C\(_{13}\)F\(_{9})\) and perinaphthenyl (C\(_{13}\)H\(_{9})\) are not an equally good choice. The role of ligand configuration in determining exchange coupling in stacks is discussed. These results would give some hints for designing new high-spin carbon-based ferromagnetic materials.
Judd Ofelt Analysis and Optical Properties of Rare Earth Doped Tellurite Glasses
Authors: Hong Tran Thi , Dung Phan Tien , Quang Vu Xuan
Published: September 2014

In this work, the structural characteristic and photoluminescence properties were investigated in Eu\(^{3 + }\) ions-doped B\(_{2}\)O\(_{3}\)-TeO\(_{2}\) --ZnO-Na\(_{2}\)O glasses. These glasses were prepared by the melting method in air, after that thermal annealed 350\rc{}C, 450\rc{}C and 550\rc{}C for different times. The analysis results of structure on these glasses showed the formation of micro-crystals in host glass after thermal annealed process. The photoluminescence spectra of Eu\(^{3 + }\) ions in these samples were observed. The local vibration mode around Eu\(^{3 + }\) ions was investigated by the phonon side band associated with \(^{7}\)F\(_{0}\)- \(^{5}\)D\(_{2}\) transition of Eu\(^{3 + }\). Judd-Ofelt parameters have been evaluated from photoluminescence spectra and were to predict the luminescence intensity ratios of \(^{5}\)D\(_{0} \to ^{7}\)F\(_{J}\) (J=2, 4 and 6) to \(^{5}\)D\(_{0} \to ^{7}\)F\(_{1}\) transition. The obtained results have been used for calculating \(\Omega_{2}\), \(\Omega _{4}\), \(\Omega _{6}\) parameters by using Judd-Ofelt theory. These \(\Omega _{2}\), \(\Omega _{4}\), \(\Omega _{6}\) parameters allow to derive radiative properties of Eu\(^{3 + }\) ions in glass material such as transition probabilities, radiative lifetimes and peak stimulated emission cross-section for the \(^{5}\)D\(_{0} \to ^{7}\)F\(_{J}\) transitions.
Influence of Annealing Conditions on Structure and Critical Parameters of Ni50Mn37Sn13 Magnetocaloric Material
Authors: Dan Nguyen Huy , An Nguyen Manh
Published: September 2014

In this paper, we present the influence of annealing conditions on structure and magnetic behavior of Ni\(_{50}\)Mn\(_{37}\)Sn\(_{13}\) magnetocaloric alloy prepared by arc-melting technique. The results show that the almost single phase of the full Heusler structure of Ni\(_{2}\)MnSn could be achieved by appropriate annealing. The transformation between martensite and austenite phases, and multi-magnetic phase behavior are observed more clearly with higher fraction of Ni\(_{2}\)MnSn phase. By using Arrott-Noaks method, critical parameters were determined to be \(\beta   0.464 \pm  0.021\), \(\gamma  = 1.117 \pm  0.073\) and \(\delta  = 3.41\), which lay between mean-field model (\(\beta  = 0.5\) and \(\gamma = 1\), \(\delta  = 3\)) with long-range ferromagnetic orders and 3D Heisenberg model (\(\beta  = 0.365\), \(\gamma = 1.336\), \(\delta {\rm g}= 4.66\)) with short-range ferromagnetic orders. The calculated results are in good accordance with the experimentally observed coexistence of weak-ferromagnetic martensite and strong-ferromagnetic austenite phases.
Influence of Blocking Effect and Energetic Disorder on Diffusion in One-dimensional Lattice
Authors: Lan Mai Thị , Hong Nguyen Van , Nhan Nguyen Thu , Hue Hoang Van
Published: September 2014

The diffusion in one-dimensional disordered lattice with Gaussian distribution of site and transition energies has been studied by mean of kinetic Monte-Carlo simulation. We focus on investigating the influence of energetic disorders and diffusive particle density on diffusivity. In single-particle case, we used both analytical method and kinetic Monte-Carlo simulation to calculate the quantities that relate to diffusive behavior in disordered systems such as the mean time between two consecutive jumps, correlation factor and diffusion coefficient. The calculation shows a good agreement between analytical and simulation results for all disordered lattice types. In many-particle case, the blocking effect results in decreasing correlation factor F and average time \(\tau _{jump}\) between two consecutive jumps. With increasing the number of particles, the diffusion coefficient \(D_{M}\) decreases for site-energy and transition-energy disordered lattices due to the F-effect affects stronger than \(\tau\)-effect. Furthermore, the blocking effect almost is  temperature independent for both lattices.
Epitaxial Growth of High Curie-Temperature Ge1-xMnx quantum dots on Si(001) by auto-assembly
Authors: Phuong Luong Thi Kim , Nguyen An Manh
Published: September 2014

We report on successful growth of epitaxial and high Curie-temperature Ge1-xMnx quantum dots on Si (001) substrates using the auto-assembled approach. By reducing the growth temperature down to 400 °C, we show that the Mn diffusion into the Si substrate can be neglected. No indication of secondary phases or clusters was observed. Ge1-xMnx quantum dots were found to be epitaxial and perfectly coherent to the Si substrate. We also observe ferromagnetic ordering in quantum dots at a temperature higher 320 K. It is believed that single-crystalline quantum dots exhibiting a high Curie temperature are potential candidates for spin injection at temperatures higher than room temperature.
The Bulk Metric in the Theory with Two Extra Dimensions
Authors: Phat Tran Huu , Lien Phan Hong , Chung Ha Van
Published: September 2014

The metric of a warped space-time with two extra dimensions is established by means of the Einstein equations in six dimensions and the compactification of two extra dimensions on a square . It is shown that at every among two fixed points our manifold reduces to the five-dimensional Randall - Sundrum space - time and the hierarchy problem could be solved .