Viện Hàn lâm Khoa học và Công nghệ Việt Nam

Methodology for synthesizing of β- and δ-carboline via two steps reaction from 2,3-dibromopyridine and 3,4-dibromopyridine. The intermediate was prepared from the substrate with o-bromophenylboronic acid via site-selective Suzuki-Myaura reaction, then, the final products were obtained by double C-N coupling via the Ulmann reaction of the intermediate with the corresponding amine with copper catalyst.

In this paper, Fe3+ was immobilized in fly ash using a thermal procedure. Fe3+- modified fly ash was used as heterogeneous Fenton catalyst for the degradation of Reactive Blue 182 (RB 182). Some properties of raw and modified fly ashes were characterized by SEM, EDX and XRD techniques. Effects of some key operating parameters such as catalyst dose, pH, and hydrogen peroxide concentration on the treatment efficiency were studied and discussed. Kinetic rate constant of treatment process was also determined. The experimental results show that the heterogeneous Fenton technique using modified fly ash/H2O2 is a suitable method for removing RB 182 from aqueous solution. At the optimum conditions includes catalyst dose of 1 g/l; hydrogen peroxide of 3,92 mM; pH 3; contact time for 90 minutes; approximately 90% of RB 182 was removed; the kinetics fitted well for pseudo first-order reaction.

At approximately 5:00 AM on December 16, 2016, a rapid and deep-seated landslide was triggered by intense rainfall in the Van Hoi irrigation reservoir in Binh Dinh province, Vietnam. The landslide generated an impulsive wave with a height of approximately 20 m, resulting in severe damage to the reservoir operation station. This study investigated the mechanisms behind the landslide's initiation and simulated its initiation and motion processes through site surveys, ring shear tests, and the LS-RAPID simulation model. The physical tests were conducted on two soil samples from the sliding zone to examine the landslide mechanism. The results indicated that only sample 2 (a sand sample of completely weathered gneiss rock) showed a high level of landslide mobility due to its liquefaction phenomena resulting in a rapid pore water pressure development and a significant strength loss. In contrast, sample 1 (a silty sand sample of residual soils) did not exhibit this behavior due to its high shear resistance value at a steady state. The findings suggest that the sliding plane of the Van Hoi landslide formed in the completely weathered gneiss layer, and the high mobility level of sample 2 is primarily responsible for its rapid movement. Notably, the LS-RAPID model successfully reproduced the landslide process using the geotechnical properties obtained in the ring shear experiments. The simulation showed that the Van Hoi deep-seated landslide was initiated from the lower middle slope at a critical value of 0.55 for the pore water pressure ratio and traveled at a high velocity of approximately 37.0 m/s. The consistency between the computer simulation results and the on-site evidence and recorded data highlights the reliability of the LS-RAPID model as a tool for assessing landslide hazards.

Năm 2009 đê chắn sóng tại cửa Tam Quan được hoàn thành, khu vực này bị bồi một cách nhanh chóng, đặc biệt là vào mùa mưa (trùng hợp với gió mùa Đông Bắc). Các quá trình thủy thạch động lực và xói lở, bồi tụ tại cửa Tam Quan thay đổi theo mùa rõ rệt. Vào mùa mưa (từ tháng 9 tới tháng 12): Gió thịnh hành theo hướng đông bắc (NE), bắc - đông bắc (NNE), bắc (N) và tây bắc (NW). Hầu hết tốc độ gió tập trung từ cấp 2 đến cấp 5. Sóng hình thành bởi gió NE, N có ảnh hưởng lớn nhất đến khu vực cửa Tam Quan. Khi truyền vào trong luồng dẫn sóng giảm nhanh chóng và có xu thế đẩy vật liệu từ ngoài biển vào, gây nên quá trình bồi - xói xen kẽ ở khu vực cửa và trong luồng dẫn. Dòng chảy có xu thế làm vật liệu đáy di chuyển từ sông ra biển gây ra sự bồi, xói xen kẽ ở khu vực luồng dẫn. Phía ngoài cửa vật liệu được bồi trên một khu vực có dạng vòng cung xung quanh cửa. Vào mùa khô (từ tháng 1 tới tháng 8): Hướng gió chủ đạo là đông nam (SE), nam - đông nam (SSE) và nam (S) với tốc độ gió khá nhỏ, từ cấp 2 đến cấp 4. Gió hướng đông (E) có tần suất nhỏ nhưng tạo ra sóng gây tác động trực tiếp tới khu vực nghiên cứu. Độ cao sóng giảm nhanh khi truyền vào trong luồng dẫn. Tác động của sóng do gió SE có xu thế đẩy vật liệu đáy từ ngoài biển và khu vực mũi nhô Trường Xuân vào lắng đọng ở khu vực cửa. Dòng chảy sóng hình thành bên bờ bắc làm vật liệu di chuyển vào khu vực trung tâm luồng làm nông hóa khu vực này. Dòng chảy chỉ làm vật liệu đáy di chuyển vào thời điểm triều rút mạnh và lắng đọng trên một khu vực rộng, đều ở cửa nhưng với cường độ không đáng kể. Kết quả tính toán những thay đổi địa hình đáy từ 15/12/2014 đến 20/5/2015 khá phù hợp với kết quả đo đạc. Đây chính là cơ sở để đưa ra các giải pháp ổn định luồng dẫn lâu dài.

The gold nanoparticle solutions are well known as an extremely sensitive biomedical analytical tool due to the strong dependence of their absorption in the visible range on the environment. In this work, the colloidal nano golds were synthesized from metal precursor chloroauric acid (HAuCl4) using trisodium citrate dehydrate (C6H5O7Na3) as reducing and stabilizing agents. The optical characterization - absorption of colloidal gold solution have been investigated under the different synthetic conditions such as: reducing agent concentration, concentration of auric ion, pH, duration of reaction and aging time. The results show that the absorption and the stability of the colloidal gold nanoparticles depend robustly on the synthetic conditions and pH of environment.

The well known Fokker-Plank-Kolmogorov Equation Method has been developed to study random vibration in systems with hysteresis that often described by the stochastic integro-differential equations or differential equations with delay.

Migration methods play an essential role in processing ground penetrating radar data. For estimating electromagnetic propagation velocity distribution, the finite - difference migration is used because of its reliable performance with high noise conditions. To optimize this migration algorithm, we propose using energy diagram as a criterion of looking for the correct velocity. If the velocity varies laterally and vertically, split step Fourier migration is used for creating a true image of subsurface structures. We applied these steps to real data in Vietnam. The results verified on field data show that migrated images with calculated velocity from energy diagram have the best quality.

The remote sensing images, including images of MODIS, VNREDSAT-1 and altimeter, are applied for researching marine environment with the different resolutions. On the basis of different time remote sensing images, we concentrated on the assessment of several characteristics including the SST, chlorophyll-a concentration and sea surface current at the different depths in different monsoons as well. With the large areas, we used the images of MODIS and altimeter. The detailed research area focuses on the Nam Yet island, and the images of VNREDSAT-1 are used. The analysis method of environmental parameters of SST and chlorophyll-a used the regression functions based on the single and combined bands to enhance the accuracy of the analysis result. The marine parameters collected at different depths in the latest field surveys on Truong Sa archipelago in the years of 2015 and 2018 are presented in this paper. On the basis of these parameters, we can analyse the relationships and compare the real field survey data and corresponding results interpreted from remote sensing images.

This paper describes the dynamic analysis of prestressed Bernoulli beams resting on a two-parameter elastic foundation under a moving harmonic load by the finite element method. Using the cubic Hermitian polynomials as interpolation functions for the deflection, the stiffness of the Bernoulli beam element augmented by that of the foundation support and prestress is formulated. The nodal load vector is derived using the polynomials with the abscissa measured from the left-hand node of the current loading element to the position of the moving load. Using the formulated element, the dynamic response of the beams is computed with the aid of the direct integration Newmark method. The effects of the foundation support, prestress as well as excitation frequency, velocity and acceleration on the dynamic characteristics of the beams are investigated in detail and highlighted.

The 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.