Leibniz University of Hanover

About: Leibniz University of Hanover is a education organization based out in Hanover, Niedersachsen, Germany. It is known for research contribution in the topics: Finite element method & Population. The organization has 14283 authors who have published 29845 publications receiving 682152 citations.

Electric quantum walks with individual atoms.

Abstract: We report on the experimental realization of electric quantum walks, which mimic the effect of an electric field on a charged particle in a lattice. Starting from a textbook implementation of discrete-time quantum walks, we introduce an extra operation in each step to implement the effect of the field. The recorded dynamics of such a quantum particle exhibits features closely related to Bloch oscillations and interband tunneling. In particular, we explore the regime of strong fields, demonstrating contrasting quantum behaviors: quantum resonances versus dynamical localization depending on whether the accumulated Bloch phase is a rational or irrational fraction of 2� . Discrete-time quantum walks conceptually represent the simplest realization of transport in a quantum system. In essence, a spin-1=2 particle moves on a lattice in discrete steps, with the direction determined by its internal spin state. A coin operation acting on the internal states is applied at each step, allowing for the coherent coupling of spin-dependent quantum paths. The iteration of the shift and coin operation delocalizes the particle over a complex host of paths that interfere with each other, determining the relevant transport properties. Emblematic of quantum walks is, for instance, the ballistic spreading of the walker, which contrasts strikingly with the diffusive classical transport of random walks. For a review, see Ref. [1] and references therein. This quantum transport model, first introduced by Feynman while developing a path integral formulation of quantum mechanics [2], still holds great relevance because it is simple and yet very powerful. In fact, quantum walks have recently been shown to constitute a universal computational primitive [3] and to provide the basis for a series of quantum algorithms [4]. Over the past few years, it has

Porous interpenetrated zirconium-organic frameworks (PIZOFs): a chemically versatile family of metal-organic frameworks.

Abstract: We present the synthesis and characterization of porous interpenetrated zirconium-organic frameworks (PIZOFs), a new family of metal-organic frameworks obtained from ZrCl(4) and the rodlike dicarboxylic acids HO(2)C[PE-P(R(1),R(2))-EP]CO(2) H that consist of alternating phenylene (P) and ethynylene (E) units. The substituents R(1),R(2) were broadly varied (alkyl, O-alkyl, oligo(ethylene glycol)), including postsynthetically addressable substituents (amino, alkyne, furan). The PIZOF structure is highly tolerant towards the variation of R(1) and R(2). This together with the modular synthesis of the diacids offers a facile tuning of the chemical environment within the pores. The PIZOF structure was solved from single-crystal X-ray diffraction analysis. The PIZOFs are stable under ambient conditions. PIZOF-2, the PIZOF prepared from HO(2)C[PE-P(OMe,OMe)-EP]CO(2)H, served as a prototype to determine thermal stability and porosity. It is stable up to 325 °C in air as determined by using thermogravimetry and powder X-ray diffraction. Argon sorption isotherms on PIZOF-2 revealed a Brunauer-Emmett-Teller (BET) surface area of 1250 m(2) g(-1) and a total pore volume of 0.68 cm(3) g(-1).

Teachers' Gender Stereotypes as Determinants of Teacher Perceptions in Elementary School Mathematics

Abstract: This study analyzes the hypothesized biasing effect of teachers' gender stereotypes on their impressions of their students' competence and effort in mathematics. 48 teachers participated in the study and responded to the questionnaires concerning perceptions of about 300 of their third and fourth grade students. In general, teacher perceptions were consistent with stereotypes of gender differences: Boys have more developmental resources in mathematics. Furthermore, this bias in teacher perceptions of their students' resources in math is linked to the teacher's own category — based, gender role stereotypic beliefs regarding the general distribution of math talent between boys and girls. The finding is moderated by the student's performance level: It only holds for average and low achieving but not for high achieving boys and girls. In this way, students' performance level is an essential mediator-variable in the transmission of teachers' gender stereotypes.