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151.
C.?CavetEmail author C.?Michaut F.?Roy H.?C.?Nguyen S.?Bouquet C.?Sauty 《Astrophysics and Space Science》2011,336(1):183-187
The Vishniac instability is supposed to explain the fragmentation of the thin shell of shocked matter in the radiative phase
of supernova remnants. However its implication and its consequence on the morphological evolution of stellar systems is not
fully demonstrated. The present paper tackles this subject by numerical simulations and focus on the role of the adiabatic
index in the instability growth. The HYDRO-MUSCL 2D hydrodynamics code has been used to simulate the evolution of a supernova
remnant thin shell and the triggering of the Vishniac instability in this thin shell. We have studied the temporal behavior
of the perturbation. The first result of the numerical study is the existence of the Vishniac instability in the simulations.
This result is proved by the overstability process observed in the simulations as predicted by the theoretical analysis. The
second important result is the damping of the perturbation at late evolution and for all the set of parameters. Indeed the
accretion of matter onto the shock damps the instability when theoretical analysis predicts its occurrence. 相似文献
152.
Quang-Thanh Bui Quoc-Huy Nguyen Van Manh Pham Minh Hai Pham Anh Tuan Tran 《国际地球制图》2013,28(12):1300-1314
AbstractThis study examines the potentials of remotely sensed data, GIS and some machine learning classifiers and ensemble techniques in the investigation of the non-linear relationship between malaria occurrences and socio-physical conditions in the Dak Nong province of Viet Nam. Accuracy assessment was determined with Receiver Operating Characteristic (ROC) curve and pair t-test. The results showed that the area under ROC of Random Subspace ensemble model performed better than the other models based on statistical indicators. Comparing pair t-test with Area Under Curve values showed a slight difference of about 1%. Therefore ensemble techniques had significantly improved the performance of the base classifier. However, the performances might vary according to geographic locations. It is concluded that the machine learning classifiers combined with remotely sensed data and GIS is promising for malaria vulnerability mapping, and the derived maps can be used as a fundamental basis for programmes on spatial disease control. 相似文献
153.
A Luoi is a Vietnamese–Laotian border district situated in the western part of Thua Thien Hue province, central Vietnam, where landslides occur frequently and seriously affect local living conditions. This study focuses on the spatial analysis of landslide susceptibility in this 263-km2 area. To analyze landslide manifestation in the study area, causative factor maps are derived of slope angle, weathering, land use, geomorphology, fault density, geology, drainage distance, elevation, and precipitation. The analytical hierarchical process approach is used to combine these maps for landslide susceptibility mapping. A landslide susceptibility zonation map with four landslide susceptibility classes, i.e. low, moderate, high, and very high susceptibility for landsliding, is derived based on the correspondence with an inventory of observed landslides. The final map indicates that about 37% of the area is very highly susceptible for landsliding and about 22% is highly susceptible, which means that more than half of the area should be considered prone to landsliding. 相似文献
154.
Characterization of the sediment composition of tidal flats and monitoring of their spatiotemporal changes has become an important part of the sustainable management of coastal environments. To accurately classify sediments through remote sensing, a comprehensive understanding of sediment reflectance spectra is indispensable. The present laboratory-based study explores the performance of the high spatial resolution (10?×?10 m) Advanced Land Observing Satellite (ALOS) launched in 2006. Relationships between reflectance spectra (bands 1 to 4) and four typical mass physical properties were investigated under wet and dry experimental conditions for intertidal sediments sampled near the Ba Lat Estuary in northern Vietnam. Reflectance in the near-infrared region corresponding to ALOS band 4 (0.76–0.89 μm) was found (1) to have a strong negative correlation with sand content (dry wt%) under both wet and dry conditions (linear correlation coefficient r?=?–0.7859 and –0.8094, respectively), (2) to increase with decreasing relative water content (%) in a given sediment type (r?=?–0.7748 to –0.9367 for mud, sandy mud, muddy sand, and sand), (3) to have a positive correlation with organic matter content (r?=?0.7610 and 0.6460 under wet and dry conditions for contents >0.20 dry wt%), and (4) to be insignificantly correlated with mineral composition assessed in terms of contents (wt%) of quartz, clay minerals, and mica group minerals. Positive relationships between reflectance and water content for the pooled data of all sediment types (r?=?0.6395) or organic matter content contrast with previous findings, and can be attributed to close interrelationships between these properties and the predominance of sand content as controlling factor of reflectance. This study clarifies that ALOS band 4 provides the most useful imagery for intertidal monitoring because its reflectance, as simulated using the laboratory data, shows the strongest correlation with sand content. In a next step, these experimental findings should be verified by identifying the reflectance relationships at satellite image scales, and also considering the effects of other tidal flat features on reflectance, such as microtopography and biological surface characteristics. 相似文献
155.
Effects of perforated baffle on reducing sloshing in rectangular tank: Experimental and numerical study 总被引:1,自引:1,他引:0
A liquid sloshing experimental rig driven by a wave-maker is designed and built to study liquid sloshing problems in a rectangular liquid tank with perforated baffle. A series of experiments are conducted in this experimental rig to estimate the free surface fluctuation and pressure distribution by changing external excitation frequency of the shaking table. An in-house CFD code is also used in this study to simulate the liquid sloshing in three-dimensional (3D) rectangular tank with perforated baffle. Good agreements of free surface elevation and pressure between the numerical results and the experimental data are obtained and presented. Spectral analysis of the time history of free surface elevation is conducted by using the fast Fourier transformation. 相似文献
156.
The construction of S-wave velocity models of marine sediments down to hundreds of meters below the seafloor is important
in a number of disciplines. One of the most significant trends in marine geophysics is to use interface waves to estimate
shallow shear velocities which play an important role in determining the shallow crustal structure. In marine settings, the
waves trapped near the fluid–solid interface are called Scholte waves, and this is the subject of the study. In 1998, there
were experiments on the Ninetyeast Ridge (Central Indian Ocean) to study the shallow seismic structure at the drilled site.
The data were acquired by both ocean bottom seismometer and ocean bottom hydrophone. A new type of seafloor implosion sources
has been used in this experiment, which successfully excited fast and high frequency (>500 Hz) body waves and slow, intermediate
frequency (<20 Hz) Scholte waves. The fundamental and first higher mode Scholte waves have both been excited by the implosion
source. Here, the Scholte waves are investigated with a full waveform modeling and a group velocity inversion approach. Shear
wave velocities for the uppermost layers of the region are inferred and results from the different methods are compared. We
find that the full waveform modeling is important to understand the intrinsic attenuation of the Scholte waves between 1 and
20 Hz. The modeling shows that the S-wave velocity varies from 195 to 350 m/s in the first 16 m of the uppermost layer. Depths
levels of high S-wave impedance contrasts compare well to the layer depth derived from a P-wave analysis as well as from drilling
data. As expected, the P- to S-wave velocity ratio is very high in the uppermost 16 m of the seafloor and the Poisson ratio
is nearly 0.5. Depth levels of high S-wave impedance contrasts are comparable to the layer depth derived from drilling data. 相似文献
157.
This paper presents a full 2-D X/Z numerical model for sediment transport in open channels and estuaries using a two-phase (fluid–solid particle) approach. The physical concept and the mathematical background of the model are given and test-cases have been carried out to validate the proposed model. In order to illustrate its feasibility for a real estuary, the model has been applied to simulate the suspended-sediment transport and the formation of turbidity maximum in the Seine estuary. The numerical results show that the main characteristics of estuarine hydro-sediment dynamics in the Seine estuary are in fact reproduced by the proposed model. A qualitative agreement between the numerical results and the actual observations has been obtained and is presented in this paper. 相似文献
158.
Patrick J. Evans Dung Nguyen Rick W. Chappell Kent Whiting John Gillette Adria Bodour John T. Wilson 《Ground Water Monitoring & Remediation》2014,34(3):65-78
In situ biogeochemical transformation involves biological formation of reactive minerals in an aquifer that can destroy chlorinated solvents such as trichloroethene (TCE) without accumulation of intermediates such as vinyl chloride. There is uncertainty regarding the materials and geochemical conditions that are required to promote biogeochemical transformation. The objective of this study was to identify amendments and biogeochemical conditions that promote in situ biogeochemical transformation. Laboratory columns constructed with plant mulch were supplemented with different amendments and were operated under varying conditions of water chemistry and hydraulic residence time. Four patterns of TCE removal were observed: (1) no removal, (2) biotic transformation of TCE to cis‐1,2‐dichloroethene (cis‐1,2‐DCE), (3) biogeochemical transformation of TCE without accumulation of reductive dechlorination products, and (4) mixed behavior where a combination of patterns was observed either simultaneously or over time. Principal coordinates analysis and analysis of variance (ANOVA) identified factors that promoted biogeochemical transformation: (1) high influent sulfate concentration, (2) relatively high hydraulic retention time, (3) supplementation of mulch with vegetable oil, and (4) addition of hematite or magnetite. The combination of the first three factors promoted complete sulfate reduction and a high volumetric sulfate consumption rate. The fourth factor provided a source of ferrous iron and/or a surface to which sulfide could react to form reactive iron sulfides. Many columns demonstrated either no TCE removal or a biotic TCE transformation pattern. Modification of column operation to include all four factors identified above promoted biogeochemical transformation in these columns. These results support the importance of the factors in biogeochemical transformation. 相似文献
159.
Nguyen Minh Truong Vu Thanh Hang Roger A. Pielke Sr. Christopher L. Castro Koji Dairaku 《Asia-Pacific Journal of Atmospheric Sciences》2012,48(4):433-448
The Mei-yu front system occurring from 23 to 27 June 1999 consists of the Mei-yu front and the dewpoint front, which confine a warm core extending from the eastern flank of the Tibetan Plateau to the west of 145°E. To further understand the synopticscale physical mechanisms associated with the Mei-yu front system, the present study proposes another insight into the physical significance of the x-component relative vorticity (XRV) whose vertical circulation is expected to tilt isentropic surfaces. The XRV equation diagnoses exhibit that the twisting effect of the planetary vorticity (TEPV) is positive along the Mei-yu front and negative in the dewpoint front region, and tilts isentropic surfaces from south to north in the Mei-yu frontal zone. Conversely, the meridional gradient of the atmospheric buoyancy (MGAB) tilts isentropic surfaces in the opposite direction and maintains negative in the regions where the TEPV is positive and vice versa. Thus, the TEPV plays the role of the Mei-yu frontogenesis, whereas the MGAB demonstrates the Meiyu frontolysis factor. Both terms control the evolution of the cross-front circulation. The other terms show much minor contributions in this case study. The present simulations also indicate that the weakening of the upper-level jet evidently induces the weakening of the Mei-yu front and reduces the amplitude of the East Asia cold trough. Furthermore, the impact can also penetrate into the lower troposphere in terms of mesoscale disturbances and precipitation, proving that the upper-level jet imposes a noticeable top-down influence on the Mei-yu front system. 相似文献
160.
Shakirov R. B. Hung Duong Quoc Syrbu N. S. Anh Le Duc Obzhirov A. I. Borzova O. V. Okulov A. K. Van Nam Bui Van Diep Nguyen Dong Mai Duc Legkodimov A. A. Shakirova M. V. Ponomareva A. L. Bakunina M. S. 《Doklady Earth Sciences》2019,484(2):181-184
Doklady Earth Sciences - This paper reports the results of the third Russian–Vietnamese expedition (V.I. Il'ichev Pacific Oceanological Institute, Far East Branch, Russian Academy of... 相似文献