In this paper we constructed a special time-changed Lévy process by a coupled continuous time random walk (CTRW). Then we derived the governing equation for the process. When the time process was the inverse process of three different subordinators, the corresponding expressions of governing equations and moments of all orders were analyzed respectively.
In this paper, by using the theory of semigroup, contractive function and the method of defining functionals, the existence of the global attractors for nondamping weak dissipative abstract evolution equations with strong solutions in the space V2θ×Vθ×Lμ2(R+;V2θ was obtained when the nonlinear term satisfies the weaker dissipative condition.
The existence and asymptotic estimates of solutions for a class of singularly perturbed boundary value problems with discontinuous coefficients are investigated in this paper. Firstly, by using the Schauder fixed point theorem, a theorem of lower-upper solutions for general problems is established. Secondly, the formal asymptotic solution is constructed by the method of boundary functions, and the existence and uniform validity of the solution are proved by using the theorem of lower-upper solutions. Finally, an example is presented as an illustration.
A new calculation on transformation semigroup preserving equivalence relation is defined and its variant semigroup derived. The definition of the natural order of the variant semigroup is given, and based on the definition, conditions that the two elements of the variant semigroup are related under the natural order are examined. Meanwhile, the elements about the natural order which are compatible are discussed. Then, the study of the natural order of transformation semigroup preserving equivalence relation is promoted.
In this paper we study quasisymmetric minimality of homogeneous perfect sets. By using principle of mass distribution, we prove that a class of homogeneous perfect sets of Hausdorff dimension 1 is quasisymmetrically Hausdorff minimal. A similar result for quasisymmetrically packing minimality is also obtained.
On the basis of some famous conjugate gradient algorithms, a class of new nonlinear conjugate gradient algorithm is proposed for solving unconstrained optimization problems, which can generate sufficient descent directions at each iteration regardless of any line search. Under the Wolfe line searches, the global convergence of the proposed algorithm is proved. Numerical experiment results show that the proposed method is promising.
A joint construction model for multi-period medicine reverse logistics network was introduced to recycle expired drugs or used medical equipment with the consideration of carbon emissions. Then the feasibility of the model was validated with a numerical example by adopting genetic algorithm (GA). The results reveal that, compared with traditional single-period reverse logistics system, the multi-period system is dynamic and the total cost of system is minimized with the significant decreasing of carbon emissions. Furthermore, this research provides a reference for building a regional medicine reverse logistics network which reduces the operation costs and responds to the national energy-saving emission reduction call.
The traffic accident severity is affected by many factors. It is suitable for modeling and forecasting by using the artificial neural network (ANN). Because standard BP(back propagation) neural network has the defect of slow convergence, based on the improved BP neural network with adaptive learning and additional momentum factor[1], so the additional momentum factor was made to be self-learning for further optimization and improvement. Using the improved BP neural network algorithm, the public traffic accident data set in Leeds of England was selected to construct and train the neural network to predict the latest records. The data set includes many kinds of influencing factors and accident severity. After a lot of experiments, by comparing the convergence rate and prediction results, it has been proved that the improved algorithm has faster convergence rate and higher forecasting accuracy rate.
In order to improve the classification accuracy, the new representation of samples can be gotten by distance metric learning. According to mahalanobis distance does not take the difference of the relativity between different classes of sample dimensions into consideration. A new supervised distance metric learning algorithm called independent discrimi-native component analysis(I-DCA) is proposed and applied to classify the motor and sensory nerve based on k nearest neighbor (kNN) algorithm. By contrast, the article also involves the analysis of two existing distance metric learning algorithms in detail, the relevant component analysis (RCA) and the discrimi-native component analysis(DCA). Compared with the mahalanobis distance, the results indicate that the classification precision of the improved algorithm increases by nearly 45%, and it is also greater than 15% compared to the RCA and DCA method. The improved classification precision shows the effectiveness of the new algorithm applied in nerve classification.
Visibility graph has provided much insight to study the dynamics of time series from the perspective complex network. We construct visibility graphs for time series from both auto-regressive stochastic and fractional Brownian motions. Our results suggest that degree distributions of the resulted complex networks of auto-regressive processes are characterized by exponential forms, while that of fractional Brownian motions obey power-law forms. Our conclusions hold for both the traditional visibility graph and its variant horizontal visibility graph.
The parton distribution functions of nucleons and mesons are basic physical quantities, while different research groups have got different results. With a very simple model that kaon is made up of only valence quarks at a low Q2 scale, the gluons and sea quarks are generated completely through the quantum chromodynamics (QCD) radiations. The modified dokshitzer-gribov-lipatov-altarelli-parisi (MD-DGLAP) equations is used as the QCD dynamical evolution equations. It is shown that the results can fit the experiments well. Compared the parton distributions and momentum distributions with the other models, the differences are obvious. We hope that future experiments can check them.
This paper studies the dynamics of femtosecond laser-induced periodic ripples on silver film by a time-resolved pump-probe imaging method. After 1-6 pump pulses irradiation, the temporal evolution of the periodic ripples on sample surface is observed. The premier ripples appear in the initial 50-70 ps after the second fs laser irradiation, and the ripple positions keep unmoved until the formation processes is completed in 1 000 ps. The results indicate that the periodic deposition of laser energy during the interaction between femtosecond laser pulses and sample surface plays a dominant role in the formation of periodic ripples, which is caused by the excitation of surface plasmon polariton During the solidification process, some ripples become shallow and even disappear because of surface melting.
γ-Si3N4 is a nitrogen-based ultra-hard ceramic with Si atoms occupying both tetrahedral and octahedral sites in a spinel structure. Based on first-principles calculations, we investigate spin-polarized electronic structures and energetic stabilities of oxygenvacancy complex center (VSiON) consisting of a substituted oxygen atom and an adjacent tetrahedrally coordinated silicon vacancy in spinel silicon nitride (γ-Si3N4) with different charge states. We find that the negatively charged VSiON-1 center is stable in the p-type γ-Si3N4 and the defect center possesses an S=1 triplet ground state and a spin-conserved excited state with low excitation energy. By using a mean-field approximation, we estimate that the spin coherence time of VSiON is 0.4 s at T=0 K, which indicates that the VSiON-1 center is a promising candidate for spin coherent manipulation and qubit operation.
Organotin compounds can lead to the unique malformations in vertebrate embryos after waterborne exposure, but the toxicity of organotin compounds to embryos through maternal transfer is still lack. In the present study, Xenopus tropicalis embryos were exposed to triphenyltin (TPT), the agonist (rosiglitazone, Rosi) and antagonist (T0070907) of peroxisome proliferator activated receptor gamma (PPARγ) through microinjection. Compared with the control, the survival rates and body length of embryos were significantly decreased in treatment groups. The survival rates were 46.9% (5 ng TPT), 42.7% (80 ng Rosi) and 54.2% (10 ng T0070907). The whole body lengths were reduced by 27% (5 ng TPT), 22% (80 ng Rosi) and 57% (20 ng T0070907). Three chemicals caused a variety of malformations including microcephaly, turbid lens of eyes and small eyes. These results indicated that PPARγ played an important role in embryonic development especially for eyes and brain development of Xenopus tropicalis. The phenotypes of malformation induced by TPT and T0070907 groups were highly identical, which suggested that the toxic mechanism of TPT might be related to PPARγ. After TPT treatment, brain and eye marker gene expression in embryos at stage20 and stage25 was detected using whole mount in situ hybridization. The results showed that en2, bf1, krox20 and pax6 expression regions were gradually decreased with the increase of the TPT doses. Quantitative PCR results further confirmed that TPT could affect the head and eye marker gene expression in neural and early tailbud stages. All the results indicated that organotin compounds showed high teratogenicity and neurotoxicity to vertebrate embryos.
The Changjiang estuary (CE) is influenced by tropical storm surges in summer, and extratropical storm surges in winter. However, there has been limited research on the latter and numerical hindcast/forecast model. Therefore,a forecasting model for extratropical storm surges is set up for the CE and adjacent region using mesoscale weather model WRF, hydrodynamic model ADCIRC and coupled with nearshore wave model SWAN. The observed data of wind and water levels were used to make extensive model calibration, especially the hindcast validation, and the overall average relative error is less than 10%, which indicates excellent model precision and reliability. Based on this hindcast/forecast model, the major characteristics and mechanism of winter extratropical storm surges around the CE has been discussed and analyzed. And the contribution of wind stress and air pressure on the surge has been quantitatively revealed. The surge's response to the wind direction is also discussed.
The three dimensional numerical model of thermal discharge water in the Changjiang estuary was established to simulate the transport and diffusion of thermal discharge water from the Huaneng Shidongkou first power plant under second-phase rebuild project and the whole power plants in the estuary in summertime, and analyze their impacts on the sensitive targets. The thermal discharge water transports and diffusions downstream along the south coast of the South Branch affected by the runoff and mixing. In the case of only considered the project, there appeared area of temperature rise of greater than 2.0℃ near the drain outlet, while the impact is weak and the temperature rise is only 0.04℃ in the water intake. The area of whole tide-averaged surface temperature rise of 3.0, 2.0 and 1.0℃ is 0.12, 0.60 and 1.42 km2, respectively. The tidal and week averaged temperature rise envelope of 1℃ does not enter the water source protection area of Chenhang reservoir. In the case of considered the whole power plants in the estuary, the area of temperature rise of greater than 1.0℃ is wider, mainly distributes along the south coast of the South Branch in 50 km range from Taicang power plants to the downstream coast of Waigaoqiao power plants. The temperature rise is significant and appears wider area of greater than 4℃ near the Huaneng power plants and downstream water. The areas of whole tide-averaged temperature rise of 3.0, 2.0, 1.0℃ reach 2.34, 4.16, 13.52 km2, respectively. The temperature rise is higher and stratification near the coast, and decreases off the coast along the sections cross the water intake and drain outlet of the project. The isotherm of temperature rise of 1℃ invades the water source protection area of Chenhang reservoir. The area of temperature rise of 1℃ averaged during spring, middle, neap and week reaches 1.9, 1.82, 1.75 and 1.83 km2 in the secondary water source reserve of Chenhang reservoir. There is no impact of thermal discharge water from the whole power plants in the Chnagjiang Estuary on the water source protection area of Qingcaosha and Dongfeng xisha reservoir, Jiuduansha wetland nature reserve and Chongming Estern shoal birds nature reserve.
This paper introduced a method of estimating extreme water level of multi-year return periods where observed data were inadequate, with the instance of Daxiedao Petrochemical Zone in Ningbo, Zhejiang. Strong weather processes caused annual maximum elevations in the past 25 years were chosen, modelled and validated based on observed wind and water elevation data of 2 nearby ocean stations, Dinghai and Zhenhai. By using well validated wind data from WRF model and the ADCIRC storm surge model, 25 years of annual maximum elevations at Daxiedao Petrochemical Zone were simulated and corrected by using the weight-averaged correlation between the model and observation in 2 ocean stations. The extreme water level of multi-year return periods was analyzed based on Gumbel distribution assumption and used for the ocean engineering design and risk investigation.
中国综合性科技类核心期刊(北大核心)
