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  • 1
    Publication Date: 2017-11-01
    Description: Multiples are usually regarded as noise in conventional seismic data processing. However, multiples are also real reflections from structural interfaces in the subsurface. Compared with primaries, multiples usually provide more balanced illumination and contain more structural information because of the smaller reflection angles and longer wavepaths. Instead of multiple suppression, multiple imaging has attracted increasingly more attention in recent years. The most commonly used migration method for multiples is performed by replacing the source wavelet with recorded data and using separated multiples as the receiver record. Then, the image of the multiples is obtained by the application of the crosscorrelation imaging condition, which is widely used in conventional migration. However, during the imaging procedure, events are matched based on their propagation times only. Crosscorrelation of unrelated events leads to heavy crosstalk, and image artifacts are introduced in the image of multiples. To overcome this shortcoming, we have introduced the stereographic imaging condition for the one-way wave-equation migration of multiples. By adding a local-slope constraint (the local slope of the extrapolated wavefields at every position and time), the stereographic imaging condition takes the local spatial coherence of the extrapolated wavefields into account. Events can be matched based not only on the propagating times but also the local slopes. Therefore, crosstalk artifacts caused by the interference of unrelated events can be efficiently suppressed. Furthermore, to improve the computational accuracy and efficiency of our approach, plane-wave destructors are introduced to estimate the reflector slopes. In this way, the need for excessive loops over the local slopes in the x - z domain during application of the stereographic imaging condition can be avoided by selecting the local slopes in a proper range. Better migration results of multiples are obtained in numerical tests, which verify the feasibility and effectiveness of our approach.
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 2016-03-11
    Description: MiR-125a-5p decreases after long non-coding RNA HOTAIR knockdown to promote cancer cell apoptosis by releasing caspase 2 Cell Death and Disease 7, e2137 (March 2016). doi:10.1038/cddis.2016.41 Authors: L Tang, H Shen, X Li, Z Li, Z Liu, J Xu, S Ma, X Zhao, X Bai, M Li, Q Wang & J Ji
    Electronic ISSN: 2041-4889
    Topics: Biology , Medicine
    Published by Springer Nature
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  • 3
    Publication Date: 2014-08-08
    Description: In order to validate the accuracy of estimated Green’s functions (EGFs), which are widely used in ambient seismic noise tomography, a broadband seismograph was installed in the epicentral area of an M  5 earthquake, with ground-truth location from Interferometric Synthetic Aperture Radar observations. EGFs between this station and permanent stations are compared with surface waves excited by the earthquake. The group velocity dispersion measured from EGFs at large interstation distances (~1000 km or longer) are consistent with measurements from the earthquake, and the EGFs from symmetric noise correlation functions (NCFs) are usually more accurate. At shorter interstation distances (300–1000 km), the match between noise and earthquake dispersion is good for most stations, although we observed mismatch for a few stations. The mismatch is probably caused by low signal-to-noise ratio of NCFs or nondiffusive noise wavefield at short distances. Online Material: Figure showing mismatch of group velocity dispersion between earthquake and noise data, and figure of phase velocity dispersion between earthquake data and noise correlation functions at station ENH.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 4
    Publication Date: 2015-08-05
    Description: By adjusting the focus geometry of a spatially structured laser pulse, single, double, and treble quasi-monoenergetic electron beams were generated, respectively, in laser-wakefield acceleration. Single electron beam was produced as focusing the laser pulse to a single spot. While focusing the laser pulse to two spots that are approximately equal in energy and size and intense enough to form their own filaments, two electron beams were produced. Moreover, with a proper distance between those two focal spots, three electron beams emerged with a certain probability owing to the superposition of the diffractions of those two spots. The energy spectra of the multiple electron beams are quasi-monoenergetic, which are different from that of the large energy spread beams produced due to the longitudinal multiple-injection in the single bubble.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 5
    Publication Date: 2019
    Description: 〈p〉The ruminants are one of the most successful mammalian lineages, exhibiting morphological and habitat diversity and containing several key livestock species. To better understand their evolution, we generated and analyzed de novo assembled genomes of 44 ruminant species, representing all six Ruminantia families. We used these genomes to create a time-calibrated phylogeny to resolve topological controversies, overcoming the challenges of incomplete lineage sorting. Population dynamic analyses show that population declines commenced between 100,000 and 50,000 years ago, which is concomitant with expansion in human populations. We also reveal genes and regulatory elements that possibly contribute to the evolution of the digestive system, cranial appendages, immune system, metabolism, body size, cursorial locomotion, and dentition of the ruminants.〈/p〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 2018-10-31
    Description: China-Mongolia-Russia Economic Corridor is a key strategic area that China, Mongolia, and Russia are all dedicated to developing. However, China-Mongolia-Russia Economic Corridor cover three countries, and passes through multiple geographical units, and there are huge differences in economic, social, and ecological development within the regions. The construction of China-Mongolia-Russia Economic Corridor has many potential risks. Therefore, this paper studied the current socio-economic and environmental situation of main regions along the China-Mongolia-Russia Economic Corridor, including Primorski Krai, Khabarovsk Krai, Amur oblast of Fareast Region, Irkutsk oblast, Zabaykalsky Krai and Republic of Buryatia of Baikal region and Novosibirsk region, Mongolia, and Liaoning, Jilin and Heilongjiang of Northeast China. Then we revealed the main ecological environment risks, and put forward green development mode to achieve sustainable socio-ecological-economic development of the cor...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
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  • 7
    Publication Date: 2018-10-31
    Description: Strengthening tourism cooperation in border areas along the China–Mongolia–Russia Economic Corridor (CMREC) are important and challenging, under “Belt and Road” (B&R) initiative. Research has constructed a tourism competitiveness evaluation model including three dimensions and based on six factors: natural resources, cultural resources, tourism market, social economy, traffic facilities, and policy support. The results show the spatial characteristics of tourism competitiveness ordered as Beijing–Tianjin–Hebei of China, Northeast China, Northwest China, Russian Siberia Federal District, Mongolia, Russian Far East Federal District, and Russian Ural Federal District. Data show that the average tourism competitiveness of the three areas in Northern China are 2.69 times those of the three Russian areas, and 1.74 times those of Mongolia; at the same time, the average tourism competitiveness of Mongolia is 1.54 times that of the three areas of Russia. Based on the evaluation resul...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
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  • 8
    Publication Date: 2017-09-19
    Description: Anisotropic and attenuating properties of subsurface media cause amplitude loss and waveform distortion in seismic wave propagation, resulting in negative influence on seismic imaging. To correct the anisotropy effect and compensate amplitude attenuation, a compensated-amplitude vertical transverse isotropic (VTI) least-squares reverse time migration (LSRTM) method is adopted. In this method, the attenuation term of an attenuated acoustic wave equation is extended to a VTI quasi-differential wave equation, which takes care of effects from anisotropy and attenuation. The finite-difference method is used to solve the equation, in which attenuation terms are solved in the wavenumber domain, and other terms are solved in the space or wavenumber domain. Stable regularization operators are derived and introduced to the equations to eliminate severe numerical noise in high-frequency components during backward propagation. Meanwhile, a demigration operator, migration operator, and gradient formula for attenuated VTI media are derived to implement the amplitude-compensated VTI LSRTM. Test of a homogeneous model proves the accuracy of the attenuated VTI quasi-differential equations and the effectiveness of the regularization operators. A numerical example for a modified Marmousi model verifies the accuracy and superiority to the amplitude-compensated VTI LSRTM. Our results show that the sensitivity to anisotropic parameters is much higher than that to the Q parameters.
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
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  • 9
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    Society of Exploration Geophysicists (SEG)
    Publication Date: 2017-07-23
    Description: The traditional high-order finite-difference (FD) methods approximate the spatial derivatives to arbitrary even-order accuracy, whereas the time discretization is still of second-order accuracy. Temporal high-order FD methods can improve the accuracy in time greatly. However, the present methods are designed mainly based on the acoustic wave equation instead of elastic approximation. We have developed two temporal high-order staggered-grid FD (SFD) schemes for modeling elastic wave propagation. A new stencil containing the points on the axis and a few off-axial points is introduced to approximate the spatial derivatives. We derive the dispersion relations of the elastic wave equation based on the new stencil, and we estimate FD coefficients by the Taylor series expansion (TE). The TE-based scheme can achieve ( 2M )th-order spatial and ( 2N )th-order temporal accuracy ( N 〈 5 ). We further optimize the coefficients of FD operators using a combination of TE and least squares (LS). The FD coefficients at the off-axial and axial points are computed by TE and LS, respectively. To obtain accurate P-, S-, and converted waves, we extend the wavefield decomposition into the temporal high-order SFD schemes. In our modeling, P- and S-wave separation is implemented and P- and S-wavefields are propagated by P- and S-wave dispersion-relation-based FD operators, respectively. We compare our schemes with the conventional SFD method. Numerical examples demonstrate that our TE-based and TE + LS-based schemes have greater accuracy in time and better stability than the conventional method. Moreover, the TE + LS-based scheme is superior to the TE-based scheme in suppressing the spatial dispersion. Owing to the high accuracy in the time and space domains, our new SFD schemes allow for larger time steps and shorter operator lengths, which can improve the computational efficiency.
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
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  • 10
    Publication Date: 2017-11-09
    Description: To predict the fabric appearance quality from the yarn structure, a yarn surface-area measurement system is proposed. We characterize the fabric appearance quality based on its surface area (Coefficient of the variance of the fabric surface area ( FSCV )) to evaluate the irregularity of the simulated fabrics. The simulated fabrics are processed by YSMS using an improved mathematical model in which the yarn with elleptical cross-section is flattened in the weaving process. Results confirm our method is viable and could help to quantify fabric appearance quality objectively. On the basis of our method, the fabric structure and appearance could be optimized and even controlable prepared with appropriate yarn.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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