Antiferromagnetic Dimers of Ni(II) in the S=1 Spin-Ladder Na_2Ni_2(C_2O_4)_3(H_2O)_2

We report the synthesis, crystal structure and magnetic properties of the S=1 2-leg spin-ladder compound Na_2Ni_2(C_2O_4)_3(H_2O)_2. The magnetic properties were examined by magnetic susceptibility and pulsed high field magnetization measurements. The magnetic excitations have been measured in high field high frequency ESR. Although the Ni(II) ions form structurally a 2-leg ladder, an isolated dimer model consistently describes the observations very well. The analysis of the temperature dependent magnetization data leads to a magnetic exchange constant of J=43 K along the rungs of the ladder and an average value of the g-factor of 2.25. From the ESR measurements, we determined the single ion anisotropy to D=11.5 K. The validity of the isolated dimer model is supported by Quantum Monte Carlo calculations, performed for several ratios of interdimer and intradimer magnetic exchange and taking into account the experimentally determined single ion anisotropy. The results can be understood in terms of the different coordination and superexchange angles of the oxalate ligands along the rungs and legs of the 2-leg spin ladder.Comment: 8 pages, 10 figure

Impact analysis of accidents on the traffic flow based on massive floating car data

The wide usage of GPS-equipped devices enables the mass recording of vehicle movement trajectories describing the movement behavior of the traffic participants. An important aspect of the road traffic is the impact of anomalies, like accidents, on traffic flow. Accidents are especially important as they contribute to the the aspects of safety and also influence travel time estimations. In this paper, the impact of accidents is determined based on a massive GPS trajectory and accident dataset. Due to the missing precise date of the accidents in the data set used, first, the date of the accident is estimated based on the speed profile at the accident time. Further, the temporal impact of the accident is estimated using the speed profile of the whole day. The approach is applied in an experiment on a one month subset of the datasets. The results show that more than 72% of the accident dates are identified and the impact on the temporal dimension is approximated. Moreover, it can be seen that accidents during the rush hours and on high frequency road types (e.g. motorways, trunks or primaries) have an increasing effect on the impact duration on the traffic flow

A multitechnique approach to weakly chemi-sorbed phases: N2 on Ni{110)

Complete characterization of an adsorbate system requires that many physical and chemical properties be determined from experimental data. Important quantities include: (1) the structure of the adsorbate phases; (2) thermodynamic quantities such as heats and entropies of adsorption and desorption; and (3) kinetic parameters which describe adsorption, desorption and ordering processes in the adsorbate phase. No single experimental technique can provide all of the necessary data over the complete range of coverages and temperatures and several techniques are usually required to minimize experimental ambiguities and artifacts. This review demonstrates the utility of such a multitechnique approach by describing a complete study of the chemisorption of molecular nitrogen of the nickel (110) surface. The techniques used are low-energy electron diffraction (LEED), ion scattering spectroscopy (ISS), infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), work function change measurements, and thermal desorption spectroscopy (TDS). The data from these experimental studies are correlated and used to test theoretical models. Extensive physical and chemical data for the N2/Ni(110) system are presented and compared with that of other molecular adsorption systems

The effect of attractive lateral interactions on flash-desorption spectra

We will discuss the effect of attractive lateral interactions on flash-desorption spectra for molecular and dissociatively adsorbed species. Attractive interactions lead to characteristic coverage dependent variations in the shape and in the temperature maximum of desorption peaks which are quite distinct from desorption traces without lateral interactions. These variations are modelled for first and second order desorption kinetics with and without precursor states. As an example for attractive lateral interactions we will present flash-desorption results of moleculary adsorbed N2 on a Ni(110) surface

XPS as a tool to study the kinetics and thermodynamics of molecular adsorption: N2 on Ni(110)

We describe the application of X-ray photoelectron spectroscopy (XPS) to the study of the kinetics and thermodynamics of molecular N2-adsorption on a Ni(110) surface. Adsorption isotherms and isobars were recorded by continuously monitoring the intensity of the 406.7 eV N 1s “shake up” peak. From these data isosteric heats of adsorption were calculated which are in good agreement with the results obtained by thermal-desorption spectroscopy and surface potential measurements. The general applicability and the limits of this method will be discussed

Thermodynamic and kinetic parameters of molecular nitrogen adsorption on Fe{111}

We describe thermal desorption experiments and their computer simulations together with thermodynamic equilibrium measurements for molecular nitrogen adsorption on an Fe{111} surface. Three distinct nitrogen adsorption states, labeled δ, γ, and α with increasing desorption temperature, are detected and it is found that adsorption into the π‐bonded α state occurs via the δ and γ states at low substrate temperatures. The δ state can act as a precursor for the γ state at T <100 K, but at higher temperatures the direct channel from the gas phase into the γ state predominates the adsorption/desorption kinetics. The activation energy of desorption for γ‐N2 is found to be ∼10% lower than the isosteric heat of adsorption indicating the possibility of dynamical effects in the desorption process into vacuum. It was also observed that preadsorbed α‐N2 increases the heat of adsorption for γ‐N2 which is evidence for a mutually attractive interaction between those two states