Knife-edge based measurement of the 4D transverse phase space of electron beams with picometer-scale emittance

Precise manipulation of high brightness electron beams requires detailed knowledge of the particle phase space shape and evolution. As ultrafast electron pulses become brighter, new operational regimes become accessible with emittance values in the picometer range, with enormous impact on potential scientific applications. Here we present a new characterization method for such beams and demonstrate experimentally its ability to reconstruct the 4D transverse beam matrix of strongly correlated electron beams with sub-nanometer emittance and sub-micrometer spot size, produced with the HiRES beamline at LBNL. Our work extends the reach of ultrafast electron accelerator diagnostics into picometer-range emittance values, opening the way to complex nanometer-scale electron beam manipulation techniques

Dual-stage structural response to quenching charge order in magnetite

The Verwey transition in magnetite (Fe_{3}O_{4} ) is the prototypical metal-insulator transition and has eluded a comprehensive explanation for decades. A major element of the challenge is the complex interplay between charge order and lattice distortions. Here we use ultrafast electron diffraction (UED) to disentangle the roles of charge order and lattice distortions by tracking the transient structural evolution after charge order is melted via ultrafast photoexcitation. A dual-stage response is observed in which X_{3}, X_{1}, and Delta5-type structural distortions occur on markedly different timescales of 0.7–3.2 ps and longer than 3.2 ps. We propose that these distinct timescales arise because X_{3}-type distortions strongly couple to the trimeron charge order, whereas the Delta5- distortions are more strongly associated with monoclinic to cubic distortions of the overall lattice. Our work aids in clarifying the charge-lattice interplay using UED method and illustrates the disentanglement of the complex phases in magnetite

Dual-stage structural response to quenching charge order in magnetite

The Verwey transition in magnetite (Fe3O4 ) is the prototypical metal-insulator transition and has eluded a comprehensive explanation for decades. A major element of the challenge is the complex interplay between charge order and lattice distortions. Here we use ultrafast electron diffraction (UED) to disentangle the roles of charge order and lattice distortions by tracking the transient structural evolution after charge order is melted via ultrafast photoexcitation. A dual stage response is observed in which X3, X1, and Delta5 type structural distortions occur on markedly different timescales of 0.7 to 3.2 ps and longer than 3.2 ps. We propose that these distinct timescales arise because X3 type distortions strongly couple to the trimeron charge order, whereas the Delta5-distortions are more strongly associated with monoclinic to cubic distortions of the overall lattice. Our work aids in clarifying the charge lattice interplay using UED method and illustrates the disentanglement of the complex phases in magnetite.Comment: 7 figures and 7 table

Carrier dependent ferromagnetism in chromium doped topological insulator Cr0.2BixSb1.8−xTe3Cr_{0.2}Bi_xSb_{1.8-x}Te_3

Carrier-independent ferromagnetism of chromium doped topological insulator $Bi_xSb_{2-x}Te_3$ thin films,which cannot be explained by current theory of dilute magnetic semiconductor, has been reported recently. To study if it is related to the distinctive surface state of topological insulator, we studied the structural, magnetic and transport characters of $Cr_{0.2}Bi_xSb_{1.8-x}Te_3$ single crystals. The Curie temperature $T_c$, which is determined from magnetization and anomalous Hall effect measurements by Arrott plots, is found to be proportional to $p^{1/3}$, where p is the hole density. This fact supports a scenario of RKKY interaction with mean-field approximation. This carrier density dependent nature enables tuning and controlling of the magnetic properties by applying a gate voltage in the future science researches and spintronics applications.Comment: 6 pages, 3 figure

Incentive mechanism of 3PL/4PL company based on logistics demander and pure 3PL company

Conference Name:8th International Conference on Service Systems and Service Management, ICSSSM'11. Conference Address: Tianjin, China. Time:June 25, 2011 - June 27, 2011.IEEE Systems, Man and Cybernetics Society; Tsinghua University, Research Center for Contemporary Management; The Chinese University of Hong Kong; Nankai UniversityThe third party logistics company develops to the fourth party logistics company is a tendency, and incentive mechanism plays a vital role in the cooperation of 4PL company and 3PL company. The logistics demander, 3PL company and 4PL company are taken into consideration to analyze the optimal incentive level of 4PL company selects in this paper, and our conclusions present that it depends on the ratio of product of weight of the logistics activities and its factor coefficient and the optimal incentive level has a positive correlation with the weight of volume of logistics activities done by 3PL company. ? 2011 IEEE

Effect of modified fly ash on environmental safety of two soils contaminated with cadmium and lead

In this study, a low-temperature roasting and hydrothermal methods were used to modify the fly ash resulting in two new types of adsorption materials - modified fly ash (MFA) and artificial zeolite (ZE). These modified fly ashes, as well as a natural zeolite (ZO) were applied to two types of contaminated soils to explore their effects and mechanisms on the behavior of Cd and Pb through leaching column experiments. The bioavailable of Pb, Cd, pH, dissolved organic carbon (DOC), organic matter, as well as the microbial community changings were detected. The results showed that, 2% ZE has a significant stabilizing effect on Cd and the bioavailable fraction contents in Guanzhong (GZ) and Hunan (HN) soils decreased by 40.5% and 53.2%, respectively. However, for Pb, the 2% MFA showed a better result than that of ZE and ZO; the contents of bioavailable Pb in HN and GZ decreased by 48.3% and 30%, respectively. Furthermore, based on the Illumina NovaSep sequencing platform, 18 soil samples of GZ and HN were sequenced for microbial communities. As compared to the control blank(CK) treatment, the abundance of soil microbial communities was significantly improved in the amended soils

Vacancy engineering of oxidized Nb2CTx MXenes for a biased nitrogen fixation

The artificial nitrogen (N2) reduction reaction (NRR) via electrocatalysis is a newly developed methodology to produce ammonia (NH3) at ambient conditions, but faces the challenges in N2 activation and poor reaction selectivity. Herein, Nb-based MXenes are developed to remarkably enhance the NRR activity through the engineering of the stretched 3D structure and oxygen vacancies (VO). The theoretical studies indicate that N2 could be initially adsorbed on VO with an end-on configuration, and the potential determining step might be the first hydrogenation step. The catalysts achieve an NH3 production rate of 29.1 μg h−1 mgcat−1 and excellent Faradic efficiency of 11.5%, surpassing other Nb-based catalysts. The selectivity of NRR is assigned to the unique structure of the catalysts, including (1) the layered graphitic structure for fast electron transfer and active site distribution, (2) the reactive VO for N2 adsorption and activation, and (3) the expanded interlayer space for mass transfer.</p