Vietnam Academy of Science and Technology: Journals Online
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Nonlinear Optical Tweezers As an Optical Method for Controlling Particles with High Trap Efficiency
Get PDFOptical tweezers have seen as an essential tool for the manipulation dielectric microparticles and nanoparticles due to its non-contact action and high resolution of optical force. Up to now, there has been a lot of optical tweezers applications in the fields of biophysics, chemistry, medical science and nanoscience. Recently, optical tweezers have been theoretically and experimentally developing for the nanomechanical characterization of various kinds of biological cells. The configuration of optical tweezers has been day after day improving to enhance the trapping efficiency, spatial and temporal resolution and easy to control trapped objects. In common trend of optical tweezers improvements, we will discuss in detail of the several configurations of nonlinear optical tweezers using nonlinear materials as the added lens. We will also address the advantages of nonlinear optical tweezers, such as enhance optical efficiency, reduce trapping region, simplify controlling all-optical method. Finally, we present discussions about the specific properties of nonlinear optical tweezers used for stretch DNA molecule as example and an ideal to improve nonlinear optical tweezers using thin layer of organic dye proposed for going time
Ground displacement of the 6 July 2019 Ridgecrest earthquake from the GNSS permanent stations
No full textThe Eastern California earthquake (also known as the Ridgecrest earthquake) occurred at 03:19:53 (UTC) on the 6th of July, with a moment magnitude of 7.1. Over the region, there is an accurate network of GNSS permanent stations. Precise determination of displacements of these stations will provide important information to better understand the structure and scope of the earthquake, contributing to faster and more accurate earthquake prediction. In this paper, we used precise point positioning with ambiguity resolution to determine the co-seismic displacements of 25 GNSS stations around the epicenter for the day of the earthquake. The processing results show that the affected area being more than 100 km centered around the earthquake epicenter with the largest value being approximately 0.6 m
A United Description for Dark Matter and Dark Energy
No full textIn this paper, we show a unifying description to the dark matter and dark energy. This description does not demand dark energy with the anti-gravitational property. It also points out a lower limit of the average mass of the particles of cosmological energy (ordinary matter, dark matter and dark energy particles) eV. The coincident problem between the density of dark energy and one of matter is a clear fact
PREPARATION AND FTIR STUDIES OF PMMA/PVC POLYMER BLENDS, PVC-g-PMMA GRAFT COPOLYMERS AND EVALUATING GRAFT CONTENT
Get PDFThis study presents the qualitative and quantitative analyses of Fourier Transform Infrared (FTIR) spectra of poly(methyl methacrylate)/poly(vinyl chloride) blends (PMMA/PVC), as well as PVC-g-PMMA graft copolymers. Graft copolymerizations of methyl mathacrylate (MMA) onto PVC macromolecules were carried out mixture of cyclohexanone/N,N-dimethylformamide as solvents, dibenzoyl peroxide as initiator and nitrogen medium. FTIR spectra of PMMA/PVC blends showed that there were molecular interactions between C=O groups of PMMA and C-Cl groups of PVC. Assignments of infrared absorption bands for specific groups of PMMA/PVC blends have been contributed. Using regression method, linear calibration curve between PMMA mole content and peak areas of C=O groups in FTIR spectra of the blends has been found when C=O peak areas were multiplied by an appropriate factor. PMMA grafted content and total PMMA formed content in PVC-g-PMMA graft copolymers have been evaluated. The results showed that grafted PMMA content was increased since PVC was initiatly dechlorinated by NaOH solution. The grafted PMMA content and total formed PMMA content were 5.05 wt.% and 11.25 wt.% respectively when MMA monomers were grafted onto neat PVC and modified PVC molecules
A giant crocodile skull from Can Tho, named “Dau Sau”, represents the largest known saltwater crocodile (Crocodylus porosus) ever reported from Vietnam
Get PDFWe report on a large crocodile skull recovered from a river bank in August 2010 near Đầu Sấu Bridge, in An Binh, Ninh Kieu District, Cần Thơ Province, in southern Vietnam. As the skull from Cần Thơ, named “Đầu Sấu“ herein, is now deposited in the Vietnam National Museum of Nature, Hanoi, we reinvestigated the circumstances surrounding its discovery and provide exact measurements. Skull length (dorsal mid-point) is 70.7 cm. The morphological features confirm it is from a Saltwater crocodile (Crocodylus porosus), and not a Siamese crocodile (C. siamensis), which historically also occurred throughout the Mekong Delta of Vietnam. Skull measurements are compared with those of other large C. porosus skulls for which reliable estimates of total length are available. We also provide measurements of the prepared skull of “Lolong” (69.8 cm), a 6.17 m long C. porosus captured in the Philippines in 2011. On the basis of known skull length:total length ratios the crocodile from Cần Thơ is estimated to be 6.3-6.8 m long. The skull of Đầu Sấu is likely to have been buried for at least 100 years. We discuss the origin of the local name Đầu Sấu, which has traditional and cultural significance, and provide historical reports of crocodiles in the area. Đầu Sấu is smaller than the largest known C. porosus skull (76 cm), but is the largest ever reported from Vietnam, and one of the largest C. porosus known.
SYNTHESIS OF STARCH MODIFIED MONTMORILLONITE AS AN EFFECTIVE ADSORBENT FOR Pb (II) REMOVAL FROM WATER
Get PDFThe adsorbent is prepared by the montmorillonite co-modification with starch for the removal of Pb (II) ions from aqueous solution. The Fourier-transformed infrared (FTIR), X-ray diffraction (XRD) spectroscopies were used to determine the structure and characteristics of the adsorbent. The main factors affecting the removal of Pb (II) ions were investigated, including the effect of pH, contact time, adsorbent dosage and the initial concentration of Pb (II). Batch process can be used for adsorption and equilibrium studies. The experimental data were fitted using Freundlich and Langmuir adsorption models. The Langmuir isotherm best fitted the experimental data with R2 0.99 and maximum Pb (II) adsorption capacity of 21.5 mg/g indicated monolayer adsorption. Kinetic studies using pseudo-first-order and pseudo-second-order rate models showed that the process complied well with the pseudo second-order rate model
Mobility Edges in One-dimensional Disordered Aharonov-Bohm Rings
Get PDFWe study numerically the localization properties of the eigenstates of a tight-binding Hamiltonian model for noninteracting electrons moving in a one-dimensional disordered ring pierced by an Aharonov-Bohm flux. By analyzing the dependence of the inverse participation ratio on Aharonov-Bohm flux, energy, disorder strength and system size, we find that all states in the ring are delocalized in the weak disorder limit. The states lying deeply in the band tails will undergo a continuous delocalization-localization transition as the disorder strength in the ring sweeps from the weak to the strong disorder regime
EFFECT OF TEMPERATURE ON THE STRUCTURE AND PROPERTIES OF Fe2O3/GRAPHENE NANOCOMPOSITES SYNTHESIZED BY HYDROTHERMAL METHOD
Get PDFA simple and straightforward approach was used to prepare Fe2O3/graphene nanocomposites with different temperature conditions. The nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and photoluminescence (PL). The results show that Fe2O3 nanoparticles with size in range of 60-100 nm are anchored on the surface and filled between the graphene nanosheets at hydrothermal reaction. The PL spectrum exhibits the emission peaks appeared at ~ 650 nm and ~ 720 nm
Investigation of aerodynamics and longitudinal stability of unmanned aerial vehicle with elevator deflection
Get PDFThe elevator is usually hinged to the horizontal tail, which acts as a balance and controls the altitude, establishes a steady motion for the aircraft at all lift coefficients. During elevator rotating, the aircraft needs to be stable to establish a new altitude. The horizontal tail has a major role in the value of the airplane’s pitching moment (due to the long arm from the aerodynamic center of the tail to the center of gravity) for the equilibrium and stability of the aircraft. The horizontal tail should be considered as an aerodynamic component behind the main wing, influenced by the wing downwash wing rather than just a minor wing. Therefore, the aim of this study is to examine the flow through unmanned aerial vehicles (UAV) including the main wing, tail and body and to calculate the aerodynamic force on the horizontal tail when rotating the elevator using the Fluent software for the viscous flows. Small disturbance theory was used to calculate the longitudinal stability of the UAV when controlling the elevator. Flying qualities are assessed to show that changes in the aerodynamic characteristics of the wing, tail, fuselage and configuration of the UAV may be required