Author: haiyenha

Improvement of Raman enhancement factor due to the use of silver nanoparticles coated obliquely aligned silicon nanowire arrays in SERS measurements

In this paper, we present the use of silver nanoparticles coated silicon nanowire (SiNW) arrays in surface-enhanced Raman scattering (SERS) measurements with emphasis on the use of obliquely instead of vertically aligned SiNW arrays. The obliquely aligned SiNW arrays were fabricated on Si(111) substrate, and the SiNWs were coated with silver nanoparticles with sizes in the 20-40 nm range. The results showed that with the use of obliquely instead of vertically aligned SiNW arrays, the Raman enhancement factor (REF) is increased by more than one order of magnitude and can reach 1014 when malachite green is used as test sample. The mechanism causing the improvement of the REF is also discussed.

http://repository.vnu.edu.vn/handle/VNU_123/34084

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Two-point Green functions of free Dirac fermions in single-layer graphene ribbons with zigzag and armchair edges

Green function technique is a very efficient theoretical tool for the study of dynamical quantum processes in many-body systems. For the study of dynamical quantum processes in graphene ribbons it is necessary to know two-point Green functions of free Dirac fermions in these materials. The purpose of present work is to establish explicit expressions of two-point Green functions of free Dirac fermions in single-layer graphene ribbons with zigzag and armchair edges. By exactly solving the system of Dirac equations with appropriate boundary conditions on the edges of graphene ribbons we derive formulae determining wave functions of free Dirac fermions in above-mentioned materials. Then the quantum fields of free Dirac fermions are introduced, and explicit expressions of two-point Green functions of free Dirac fermions in single-layer graphene ribbons with zigzag and armchair edges are established.

http://repository.vnu.edu.vn/handle/VNU_123/34085

Emplacement and cooling of the Dien Bien Phu granitic complex: Implications for the tectonic evolution of the Dien Bien Phu Fault (Truong Son Belt, NW Vietnam)

The Dien Bien Phu (DBP) Fault strikes nearly perpendicular to the general tectonic framework, separating northwest Vietnam into two compartments. The DBP and Muong Lay granites are exposed respectively east and west of the fault. The U/Pb age of 277±2Ma obtained for the Muong Lay granite is similar to the age of the Chieng Khuong complex exposed within the Song Ma structure east of the DBP Fault. These two magmatic intrusions are considered as belonging to a same tectonic structure related to the subduction of the Song Ma Ocean under the Indochina Block during the Indosinian orogeny. The DBP Fault with a total post Permian dextral offset of 30-40km shifts the Song Ma Suture. It could then be connected to the Ailao Shan-Shuanggou suture to the north. The undeformed DBP granite gave a U/Pb age of 230±1Ma sealing the Indosinian deformation on the fault. The Ladinian-Carnian activity of the fault is confirmed by the 40Ar/39Ar (biotite) age of 228±4Ma obtained from the paragneiss forming the fault zone. A geodynamic model is proposed to describe the various tectonic phases recorded by on the DBP Fault. It associates field data, stratigraphic observations, and geochronology analyses (U/Pb, Ar/Ar, fission tracks). Following the Late Triassic exhumation of the granite and the end of the Indosinian orogeny marked by the Norian unconformity, the granite was buried under Jurassic and Lower Cretaceous sediments. A strong cooling event during the early Late Cretaceous (100Ma) is associated with the reactivation of the DBP Fault and the accommodation of a southward thrusting of the Song Da terrane onto the Truong Son Belt. This newly recognised tectonic phase could be associated to the subduction of the Paleo-Pacific plate under the Indochina Block. No data are available yet to constrain the Tertiary evolution of the DBP system. However, the Tertiary deformation is likely similar to the Cretaceous one

http://repository.vnu.edu.vn/handle/VNU_123/34086

Observation of the Bs 0→J/ψKs 0K±π∓ decay

Decays of the form B(s) 0 → J/ψ KS 0h+h(′)- (h(′) = K, π) are searched for in proton-proton collision data corresponding to an integrated luminosity of 1.0 fb-1 recorded with the LHCb detector. The first observation of the B(s) 0 → J/ψ KS 0K±π∓ decay is reported, with significance in excess of 10 standard deviations. The B0→J/ψKs 0K+K- decay is also observed for the first time. The branching fraction of B0→J/ψKs 0π+π- is determined, to significantly better precision than previous measurements, using B0→ J/ψKs 0 as a normal-isation channel. Branching fractions and upper limits of the other B(s) 0→ J/ψKs 0h+h(′)- modes are determined relative to that of the B0→ /ψKs 0π+π- decay.

http://repository.vnu.edu.vn/handle/VNU_123/34199

Batch-Theta∗ for path planning to the best goal in a goal set

The development of 3D cameras and many navigation-supporting sensors has recently enabled robots to build their working maps and navigate accurately, making path planning popular not just on computer graphics, but in real environments as well. Pursuing the solutions for robot path planning, this paper presents a variant of searching method Theta∗ for choosing the best goal among given goals and the lowest-cost path to it, called Batch-Theta∗. The novelty lies at the proposed line-of-sight checking function during the searching process and the manner that the method handles the batch of goals during one search instead of repeatedly considering a single goal or blindly doing the exhausted search. The analysis and simulations show that the proposed Batch-Theta∗ efficiently finds the lowest-cost path to the best goal in a given goal set under Theta’s mechanism.

http://repository.vnu.edu.vn/handle/VNU_123/34192

Measurement of CP asymmetry in D 0 → K – K + and D 0 → π – πdecays

Time-integrated CP asymmetries in D 0 decays to the final states K – K + and π – π + are measured using proton-proton collisions corresponding to 3fb-1 of integrated luminosity collected at centre-of-mass energies of 7 TeV and 8 TeV. The D 0 mesons are produced in semileptonic b-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in CP asymmetries between the two final states is measured to be Δ ACP = ACP (K- K +) ACP (π- π+) = (+ 0.14 ± 0.16 (stat) ± 0.08 (syst)) %. A measurement of A CP (K – K +) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D decays. It is found to be ACP (K- K+) = (- 0.06 ± 0.15 (stat) ± 0.10 (syst)) %, where the correlation coefficient between ΔA CP and A CP (K – K +) is ρ = 0.28. By combining these results, the CP asymmetry in the D 0 → π – π + channel is A CP (π – π +) = (-0.20 ± 0.19 (stat) ± 0.10 (syst))%.

http://repository.vnu.edu.vn/handle/VNU_123/34191

Measurement of polarization amplitudes and CP asymmetries in B 0 → Φk *(892)0

An angular analysis of the decay B 0 → ΦK *(892)0 is reported based on a pp collision data sample, corresponding to an integrated luminosity of 1.0 fb-1, collected at a centre-of-mass energy of sqrt{s} = 7 TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave K + π – and K + K – contributions are taken into account and found to be significant. A comparison of the B 0 → ΦK *(892)0 and {overline{B}} 0}\to \phi {overline{K}} {*}}{left({892} \right)} 0} results shows no evidence for direct CP violation in the rate asymmetry, in the triple-product asymmetries or in the polarization amplitudes and phases.

http://repository.vnu.edu.vn/handle/VNU_123/34189