The nonlinear optical response of a fluorine-containing azoic dye

The nonlinear optical nonlinearities of a fluorine-containing azoic dye in tetrahydrofuran have been investigated by using Z-scan technique with picosecond and nanosecond lasers. The experimental results reveal that the azoic dye has large optical nonlinearity under the excitations of picosecond and nanosecond 532 nm. At the picosecond 532 nm the solution presents negative nonlinear refraction due to the electronic effect, while the larger nonlinear refraction under nanosecond laser excitation is induced by thermal effect. Moreover, the different nonlinear absorption behavior under picosecond and nanosecond excitations is analyzed.     

咔咯锰(Ⅴ)氧配合物与苯乙烯的氧原子转移反应机理

采用密度泛函理论B3LYP方法研究了咔咯锰(Ⅴ)氧配合物(MnVO corrole)与苯乙烯氧原子转移(oxygen atom transfer,OAT)反应途径和吸电子取代基的影响.计算结果发现氧原子进攻苯乙烯中双键的β碳原子形成过渡态,结合内禀反应坐标法(intrinsic reaction coordinate ...     

覆盖数不超过3的图上渡河问题

1000多年前,英国著名学者Alcuin曾提出一个古老的渡河问题,即狼、羊和卷心菜的渡河问题。2006年,Prisner把该问题推广到任意的冲突图上,考虑了一类情况更一般的渡河运输问题。所谓冲突图是指一个图G=(V,E),这里V代表某些物品的集合,V中的两个点有边连结当且仅当这两个点是冲突的,即在无人监管的情况下不允许留在一起的点。图G=(V,E)的一个可行运输方案是指在保证不发生任何冲突的前提下,把V的点所代表的物品全部摆渡到河对岸的一个运输方案。图G的Alcuin数定义为它存在可行运输方案时所需船的最小容量。本文讨论了覆盖数不超过3的连通图的Alcuin数,给出了该类图Alcuin数的完全刻画。     

联图$K_5+P_n$的交叉数

A join graph denoted by G + H,is illustrated by connecting each vertex of graph G to each vertex of graph H.In this paper,we prove the crossing number of join product of K_5 + P_n is Z(5,n) + 2 n + [n/2] + 4 for n ≥ 2.     

Distribution of stable isotopes in surface water along the Danube River in Serbia†

Stable hydrogen and oxygen isotopes were analysed in water samples from the River Danube and its tributaries during a longitudinal survey performed in August 2005 on Serbian territory. Danube river water data ranged from?80‰ to?66‰ for δ²H, and from?11.2‰ to?9.3‰ for δ¹⁸O with δ values increasing downstream. The isotopic signatures of the adjacent tributaries (the Tisza, the Sava and the Velika Morava) sampled at the locations close to their confluence with the Danube (Titel, Ostru?nica and Ljubi?evski most, respectively) just about the time of the campaign were enriched (?67‰ and?63‰ for δ²H, and?9.3‰ and?8.9‰ for δ¹⁸O) with respect to the Danube water because of their catchment effects. Hydrogen and oxygen stable isotope values were used in combination with measured physico-chemical and biological parameters to trace hydrological and transport processes in these river systems. The mixing relationships between the Danube main stream and its tributaries were estimated using the mass balance for isotopic composition and electrical conductivity as conservative parameters. Evidence of an incomplete mixing process at the ?enta location, 8 km below the confluence of the Tisza river, with its participation of 88% was shown by its oxygen-18 content. The correlations between river water isotope composition and physico-chemical and biological parameters are discussed.     

Fitting of two-tensor models without ad hoc assumptions to detect crossing fibers using clinical DWI data

Analysis of crossing fibers is a challenging topic in recent diffusion-weighted imaging (DWI). Resolving crossing fibers is expected to bring major changes to present tractography results based on the standard tensor model. Model free approaches, like Q-ball or diffusion spectrum imaging, as well as multi-tensor models are used to unfold the different diffusion directions mixed in a voxel of DWI data. Due to its seeming simplicity, the two-tensor model (TTM) is applied frequently to provide two positive-definite tensors and the relative population fraction modeling two crossing fiber branches. However, problems with uniqueness and noise instability are apparent. To stabilize the fit, several of the 13 physical parameters are fixed ad hoc, before fitting the model to the data. Our analysis of the TTM aims at fitting procedures where ad hoc parameters are avoided. Revealing sources of instability, we show that the model's inherent ambiguity can be reduced to one scalar parameter which only influences the fraction and the eigenvalues of the TTM, whereas the diffusion directions are not affected. Based on this, two fitting strategies are proposed: the parsimonious strategy detects the main diffusion directions without extra parameter fixation, to determine the eigenvalues and the population fraction an empirically motivated condition must be added. The expensive strategy determines all 13 physical parameters of the TTM by a fit to DWIs alone; no additional assumption is necessary. Ill-posedness of the model in case of noisy data is cured by denoising of the data and by L-curve regularization combined with global minimization performing a least-squares fit of the full model. By model simulations and real data applications, we demonstrate the feasibility of our fitting strategies and achieve convincing results. Using clinically affordable diffusion acquisition paradigms (encoding numbers: 21, 2*15, 2*21) and b values (b = 500–1500 s/mm²), this methodology can place the TTM parameters involved in crossing fibers on a more empirical basis than fitting procedures with technical assumptions.     

Dynamic characteristics of traffic flow with consideration of pedestrians’ road-crossing behavior

Pedestrians’ road-crossing behavior can often interrupt traffic flow and cause vehicle queueing. In this paper, we propose some moving rules for modeling the interaction of vehicles and pedestrians. The modified visual angle car-following model is presented for the movement of vehicles with consideration of the lateral effect of waiting pedestrians. The pedestrians’ behavior is summarized as consisting of three steps: pedestrian arrival, gap acceptance, and pedestrian crossing. Some characteristic parameters of pedestrians are introduced to characterize pedestrians’ behavior. Simulation results show that the interaction of vehicles and pedestrians lowers the traffic capacity and increases delays to both vehicles and pedestrians.     

中水回灌城市内河实验室模拟可行性初探

将城市污水处理厂出水经过处理后作为河道景观补给水的做法正在多个城市应用，本文在假设没有外源性污染的前提下，对宁波市某污水处理厂深度处理后的中水回灌于城市内河可行性进行了实验室模拟，结果显示达到实验水质指标的中水，以每天置换1／30的流量引入受污染城市内河，在解决河道水资源紧缺问题的同时，不会对原有河道水质带来大的危害．文章还针对实际的应用提出了一些建议．     

Spin-inversion mechanisms in the reactions of transition metal cations (Sc+, Ti+, V+, Cr+, Mn+, Fe+, Co+, Ni+, and Cu+) with OCS in the gas phase: A perspective from automated reaction path search calculations

The mechanisms including spin-inversion have been systematically studied for the M⁺ + OCS → MS⁺ + CO/MO⁺ + CS (M denotes a transition metal from Sc to Cu) ion-molecule reactions using the automated reaction path search method. We used the lowest mixed-spin potential energy surface obtained from the diagonalization of the spin-coupled Hamiltonian matrix, whose diagonal elements are taken to be the lowest two spin states. This scheme can effectively locate approximate minimum energy crossing points between the two potential energy surfaces with different spin multiplicities. The spin-orbit couplings at spin-inversion points have been calculated to understand the efficiencies of nonadiabatic transitions. The obtained reaction pathways and the calculated spin-orbit couplings are employed to interpret previous experimental studies.