摘要 :
The fractional Fokker-Planck equation has been used in many physical transport problems which take place under the influence of an external force field. In this paper we examine some practical numerical methods to solve a class of...
展开
The fractional Fokker-Planck equation has been used in many physical transport problems which take place under the influence of an external force field. In this paper we examine some practical numerical methods to solve a class of initial-boundary value problems for the fractional Fokker-Planck equation on a finite domain. The solvability, stability, consistency, and convergence of these methods are discussed. Their stability is proved by the energy method. Two numerical examples are also presented to evaluate these finite difference methods against the exact analytical solutions.
收起
摘要 :
A continuum mechanics model is established for hydrogen storage in single- and multi-wall carbon nanotubes (CNTs) and the bundle of single-wall CNTs. The model accounts for the deformation of CNTs, and van der Waals interactions a...
展开
A continuum mechanics model is established for hydrogen storage in single- and multi-wall carbon nanotubes (CNTs) and the bundle of single-wall CNTs. The model accounts for the deformation of CNTs, and van der Waals interactions among hydrogen molecules and between hydrogen and carbon atoms. The analytical expressions of hydrogen storage (number of hydrogen molecules per unit volume) in CNTs are obtained, and are validated by atomistic simulations. CNTs are categorized as tiny, small, medium and large CNTs; tiny CNTs cannot achieve the goals of hydrogen storage (62 kg/m~3 and 6.5 wt% of hydrogen set by the US Department of Energy) without fracture; small CNTs are strained during hydrogen storage; medium CNTs can achieve the above goals without the strain and do not self collapse; and large CNTs may self collapse upon the release of hydrogen.
收起
摘要 :
Natural convection within closed cavities is of practical and theoretical interest in many nonlinear sciences and industrial applications. Using a simple lattice Boltzmann (LB) thermal model with the Boussinesq approximation, this...
展开
Natural convection within closed cavities is of practical and theoretical interest in many nonlinear sciences and industrial applications. Using a simple lattice Boltzmann (LB) thermal model with the Boussinesq approximation, this study investigates 2D natural convection flows with nonlinear phenomena within enclosed rectangular cavities. The simulations are performed at a constant Prandtl number of Pr = 0.71 and the reference Rayleigh numbers of Ra~*≤2 × 10~4 at the macroscopic scale (Kn = 10~(-4)) and the mesoscopic scale (Kn = 10~(-2)), respectively. In every case, an appropriate value of the characteristic velocity, i.e. V ≡ (βg_yΔTH), is chosen using a simple model based on the kinetic theory. The simulations commence to identify the convective-dominated stationary, time-independent steady flow (i.e. the primary instability condition). The spectral information of secondary instability with an oscillatory flow is then investigated using a spectrum analysis based on the fast-Fourier transform (FFT) technique. The relationship between the Nusselt number (Nu) and the reference Rayleigh number (Ra~*) is also systematically examined. In general, the simulation results show that unstable flow is generated at particular values of the Rayleigh number, Knudsen number, and cavity aspect ratio. Meanwhile, the Knudsen number and the aspect ratio play key roles in determining the evolution of oscillatory flows beyond the threshold of secondary instability.
收起
摘要 :
The progress achieved in the field of genomics in recent years is leading medicine to adopt a personalized model in which the knowledge of individual DNA alterations will allow a targeted approach to cancer. Using pancreatic cance...
展开
The progress achieved in the field of genomics in recent years is leading medicine to adopt a personalized model in which the knowledge of individual DNA alterations will allow a targeted approach to cancer. Using pancreatic cancer as a model, we discuss herein the fundamentals that need to be considered for the high throughput and global identification of mutations. These include patient-related issues, sample collection, DNA isolation, gene selection, primer design, and sequencing techniques. We also describe the possible applications of the discovery of DNA changes to the approach of this disease and cite preliminary efforts where the knowledge has been translated into the clinical or preclinical setting.
收起
摘要 :
Historical episodes of natural selection can skew the frequencies of genetic variants, leaving a signature that can persist for many tens or even hundreds of thousands of years. However, formal tests for selection based on allele ...
展开
Historical episodes of natural selection can skew the frequencies of genetic variants, leaving a signature that can persist for many tens or even hundreds of thousands of years. However, formal tests for selection based on allele frequency skew require strong assumptions about demographic history and mutation, which are rarely well understood. Here, we develop an empirical approach to test for signals of selection that compares patterns of genetic variation at a candidate locus with matched random regions of the genome collected in the same way. We apply this approach to four genes that have been implicated in syndromes of impaired neurological development, comparing the pattern of variation in our re-sequencing data with a large-scale, genomic data set that provides an empirical null distribution. We confirm a previously reported signal at FOXP2, and find a novel signal of selection centered at AHI1, a gene that is involved in motor and behavior abnormalities. The locus is marked by many high frequency derived alleles in non-Africans that are of low frequency in Africans, suggesting that selection at this or a closely neighboring gene occurred in the ancestral population of non-Africans. Our study also provides a prototype for how empirical scans for ancient selection can be carried out once many genomes are sequenced.
收起
摘要 :
Traditional information hiding algorithms cannot maintain a good balance of capacity, invisibility and robustness. In this paper, a novel blind colour image information hiding algorithm based on grey prediction and grey relational...
展开
Traditional information hiding algorithms cannot maintain a good balance of capacity, invisibility and robustness. In this paper, a novel blind colour image information hiding algorithm based on grey prediction and grey relational analysis in the Discrete Cosine Transform (DCT) domain is proposed. First, this algorithm compresses the secret image losslessly based on the improved grey prediction GM(1,1) (IGM) model. It then chooses the blocks of rich texture in the cover image as the embedding regions using Double-dimension Grey Relational Analysis (DGRA). Finally, it adaptively embeds the compressed secret bits stream into the DCT domain mid-frequency coefficients, which are decided by those blocks' Double-Dimension Grey Correlation Degree (DGCD) and Human Visual System (HVS). This method can ensure an adequate balance between invisibility, capacity and robustness. Experimental results show that the proposed algorithm is robust against JPEG compression (46.724 6 dB when the compression quality factor is 90%), Gaussian noise (45.531 3 dB when the parameter is (0,0.000 5)) etc., and it is a blind information hiding algorithm that can be extracted without an original carrier.
收起
摘要 :
In an effort to provide a technology platform for the mechanical analysis of the clothing pressure on the bust and to
investigate the relationship of clothing pressure on the bust and garment bust strain, and Young’s modulus of f...
展开
In an effort to provide a technology platform for the mechanical analysis of the clothing pressure on the bust and to
investigate the relationship of clothing pressure on the bust and garment bust strain, and Young’s modulus of fabric,
accurately, a finite element model of the standard female body bust cross-section was created. The model was composed
of skin, soft tissue and bone. The clothing pressure exerted on the busts by 10 elastic sports vests of two types of
extensibility in fabric with different bust girth and identical style was measured, then the pressure was taken as load and
applied to the model. The bust strain of 10 sports vests after wearing was calculated based on the finite element model.
The data from eight out of the 10 vests was chosen to find the linear equation of the relationship between the clothing
pressure exerted on the bust, the vest bust strain and Young’s modulus of fabric. The data from the other two vests were
used to verify the equation, and results indicated that the calculated clothing pressure was very similar to that measured,
proving that the equation can provide a database for the design, from bust size, of functional pressure comfort tight-fit
garments.
收起
摘要 :
We report the structure of an integrin with an alphaI domain, alpha(X)beta(2), the complement receptor type 4. It was earlier expected that a fixed orientation between the alphaI domain and the beta-propeller domain in which it is...
展开
We report the structure of an integrin with an alphaI domain, alpha(X)beta(2), the complement receptor type 4. It was earlier expected that a fixed orientation between the alphaI domain and the beta-propeller domain in which it is inserted would be required for allosteric signal transmission. However, the alphaI domain is highly flexible, enabling two betaI domain conformational states to couple to three alphaI domain states, and greater accessibility for ligand recognition. Although alpha(X)beta(2) is bent similarly to integrins that lack alphaI domains, the terminal domains of the alpha- and beta-legs, calf-2 and beta-tail, are oriented differently than in alphaI-less integrins. Linkers extending to the transmembrane domains are unstructured. Previous mutations in the beta(2)-tail domain support the importance of extension, rather than a deadbolt, in integrin activation. The locations of further activating mutations and antibody epitopes show the critical role of extension, and conversion from the closed to the open headpiece conformation, in integrin activation. Differences among 10 molecules in crystal lattices provide unprecedented information on interdomain flexibility important for modelling integrin extension and activation.
收起
摘要 :
White matter tracts, which play a crucial role in the coordination of information flow between different regions of grey matter, are particularly vulnerable to multiple sclerosis. Many studies have shown that the white matter lesi...
展开
White matter tracts, which play a crucial role in the coordination of information flow between different regions of grey matter, are particularly vulnerable to multiple sclerosis. Many studies have shown that the white matter lesions in multiple sclerosis are associated with focal abnormalities of grey matter, but little is known about the alterations in the coordinated patterns of cortical morphology among regions in the disease. Here, we used cortical thickness measurements from structural magnetic resonance imaging to investigate the relationship between the white matter lesion load and the topological efficiency of structural cortical networks in multiple sclerosis. Network efficiency was defined using a 'small-world' network model that quantifies the effectiveness of information transfer within brain networks. In this study, we first classified patients (n = 330) into six subgroups according to their total white matter lesion loads, and identified structural brain networks for each multiple sclerosis group by thresholding the corresponding inter-regional cortical thickness correlation matrix, followed by a network efficiency analysis with graph theoretical approaches. The structural cortical networks in multiple sclerosis demonstrated efficient small-world architecture regardless of the lesion load, an organization that maximizes the information processing at a relatively low wiring cost. However, we found that the overall small-world network efficiency in multiple sclerosis was significantly disrupted in a manner proportional to the extent of total white matter lesions. Moreover, regional efficiency was also significantly decreased in specific brain regions, including the insula and precentral gyrus as well as regions of prefrontal and temporal association cortices. Finally, we showed that the lesions also altered many cortical thickness correlations in the frontal, temporal and parietal lobes. Our results suggest that the white matter lesions in multiple sclerosis might be associated with aberrant neuronal connectivity among widely distributed brain regions, and provide structural (morphological) evidence for the notion of multiple sclerosis as a disconnection syndrome.
收起
摘要 :
The derivation of pluripotent embryonic stem (ES) cell lines has opened up new areas of research in basic and applied science, most significantly in developmental biology and regenerative medicine. While application-oriented resea...
展开
The derivation of pluripotent embryonic stem (ES) cell lines has opened up new areas of research in basic and applied science, most significantly in developmental biology and regenerative medicine. While application-oriented research has for the most part focussed on obtaining differentiated, organotypic cells from ES cells for future cell grafting therapies, ES cells have more immediate potential for use in toxicological in vitro assays used during drug development. ES cells are derived from blastocyst-stage embryos and offer an in vitro model for early development, thus enabling tests for teratogenicity testing in a human cell culture system and avoiding the pitfalls of inter-species differences. Differentiated, organotypic cells obtained from ES cells can potentially replace the primary cells and cell lines currently used for in vitro toxicology by offering a more consistent and potentially limitless source of differentiated cells. This can facilitate the establishment of comprehensive toxicogenomics and -proteomics databases and complement current databases that rely on data obtained from animal experiments. More recently, induced pluripotent stem (iPS) cells with ES cell-like properties have been obtained through reprogramming of somatic cells, thus enabling the generation of disease-specific cell lines. We review the potential of combining ES cells and ES cell-derived somatic cells with "omics" technologies for in vitro toxicology with a particular emphasis on the development of toxicogenomics and toxicoproteomics signatures. A separate section describes the potential of iPS cells for toxicology.
收起
原文获取