Magnetothermal Transport of Oriented Graphite at Low Temperatures

We have studied the magnetic field dependence of the thermal conductivity κ(T,B) of highly oriented pyrolytic graphite samples at temperatures 0.2K≤T < 10K and fields 0T≤ B ≤ 9T. The samples show clear deviations from the Wiedemann-Franz law with a kink behavior at fields B ～ 0.1 T near the metal-insulator transition observed in electrical resistivity measurements. We further show that the oscillations in the thermal conductivity at the quantum limit B > 1 T, which are correlated with the Landau quantization observed in Hall measurements, increase in amplitude with temperature following a ～ T³ law at T > 0.2 K and show a maximum at T ～ 6 K, suggesting that they are phonons mediated. PACS numbers: 72.20.My, 72.15.Eb, 73.43.-f     

Evaluation of the onset of green-up in temperate deciduous broadleaf forests derived from Moderate Resolution Imaging Spectroradiometer (MODIS) data

Vegetation phenology is the chronology of periodic phases of development. It constitutes an efficient bio-indicator of impacts of climate changes and a key parameter for understanding and modelling vegetation-climate interactions and their implications on carbon cycling. Numerous studies were devoted to the remote sensing of vegetation phenology. Most of these were carried out using data acquired by AVHRR instrument onboard NOAA meteorological satellites. Since 1999, multispectral images were acquired over the whole earth surface every one to two days by MODIS instrument onboard Terra and Aqua platforms. In comparison with AVHRR, MODIS constitutes a significant technical improvement in terms of spatial resolution, spectral resolution, geolocation accuracy, atmospheric corrections scheme and cloud screening and sensor calibration. In this study, 250 m daily MODIS data were used to derive precise vegetation phenological dates over deciduous forest stands. Phenological markers derived from MODIS time-series and provided by MODIS Global Land Cover Dynamics product (MOD12Q2) were compared to field measurements carried out over the main deciduous forest stands across France and over five years. We show that the inflexion point of the asymmetric double-sigmoid function fitted to NDVI temporal profile is a good marker of the onset of green-up in deciduous stands. At plot level, the prediction uncertainty is 8.5 days and the bias is 3.5 days. MODIS Global Land Cover Dynamics MOD12Q2 provides estimates of onset of green-up dates which deviate substantially from in situ observations and do not perform better than the null model. RMSE values are 20.5 days (bias -17 days) using the onset of greenness increase and 36.5 days (bias 34.5 days) using the onset of greenness maximum. An improvement of prediction quality is obtained if we consider the average of MOD12Q2 onset of greenness increase and maximum as marker of onset of green-up date. RMSE decreases to 16.5 days and bias to 7.5 days.     

Multidimensional BIBO stability and Jury’s conjecture

Twenty years ago E. I. Jury conjectured by analogy to the case of digital filters that a two-dimensional analog filter is BIBO stable if its transfer function has the form H = 1/P where P is a very strict Hurwitz polynomial (VSHP). In more detail he conjectured that the impulse response of the filter is an absolutely integrable function. However, he did not specify the exact equations of these filters and did not prove the existence of the impulse response. In the present paper we generalise Jury’s conjecture to arbitrary proper transfer functions H = Q/P where P is a bivariate VSHP and prove this generalisation. In particular, we show the existence of a suitable impulse response or fundamental solution for any multivariate proper rational function. However, this impulse response is a measure and not a function. We have not succeeded to prove an analogue of Jury’s conjecture in higher dimensions than two yet, but we propose a new conjecture in context with the robustly stable multivariate polynomials investigated by Kharitonov et. al. For the discrete case we prove that the structurally stable rational functions after Bose, Lin et al. coincide with the stable rational functions discussed in context with the stabilisation of discrete input/output systems. These rational functions are BIBO stable, but the converse is not true as established by several authors. Financial support of M. Scheicher through the Austrian FWF-project P18974 is gratefully acknowledged.     

A multi-method, holistic strategy for researching critical success factors in IT projects

In the field of information systems (IS) there is an observable trend towards the use of multi-method research. Using different research methods allows for the cross-validation of data obtained via multiple approaches, with the potential to increase the robustness of research results. Such a multi-method approach is applicable to a comprehensive research agenda on critical success factors, an agenda that needs to take into account not only the identification, but also the analysis and management of critical success factors. The goal of this article is to contribute new knowledge on how to carry out research on critical success factors in IS projects using a multi-method approach. For this purpose, two research projects are presented, each a variation of the research design customized to particular circumstances. First, there is an outline of the research approach taken for a critical success factor research project in the field of portal implementation, with discussion of the strengths and weaknesses of the project. Taking into consideration these experiences, the research approach of a similar critical success factor research project in the field of offshore software development is then described. Finally, recommendations for using the multi-method research approach in critical success factor research are presented.     

MNPBEM – A Matlab toolbox for the simulation of plasmonic nanoparticles

MNPBEM is a Matlab toolbox for the simulation of metallic nanoparticles (MNP), using a boundary element method (BEM) approach. The main purpose of the toolbox is to solve Maxwell?s equations for a dielectric environment where bodies with homogeneous and isotropic dielectric functions are separated by abrupt interfaces. Although the approach is in principle suited for arbitrary body sizes and photon energies, it is tested (and probably works best) for metallic nanoparticles with sizes ranging from a few to a few hundreds of nanometers, and for frequencies in the optical and near-infrared regime. The toolbox has been implemented with Matlab classes. These classes can be easily combined, which has the advantage that one can adapt the simulation programs flexibly for various applications.Program summaryProgram title: MNPBEMCatalogue identifier: AEKJ_v1_0Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEKJ_v1_0.htmlProgram obtainable from: CPC Program Library, Queen?s University, Belfast, N. IrelandLicensing provisions: GNU General Public License v2No. of lines in distributed program, including test data, etc.: 15 700No. of bytes in distributed program, including test data, etc.: 891 417Distribution format: tar.gzProgramming language: Matlab 7.11.0 (R2010b)Computer: Any which supports Matlab 7.11.0 (R2010b)Operating system: Any which supports Matlab 7.11.0 (R2010b)RAM: ?1 GByteClassification: 18Nature of problem: Solve Maxwell?s equations for dielectric particles with homogeneous dielectric functions separated by abrupt interfaces.Solution method: Boundary element method using electromagnetic potentials.Running time: Depending on surface discretization between seconds and hours.     

Geometric calibration of head-mounted displays and its effects on distance estimation

Head-mounted displays (HMDs) allow users to observe virtual environments (VEs) from an egocentric perspective. However, several experiments have provided evidence that egocentric distances are perceived as compressed in VEs relative to the real world. Recent experiments suggest that the virtual view frustum set for rendering the VE has an essential impact on the user's estimation of distances. In this article we analyze if distance estimation can be improved by calibrating the view frustum for a given HMD and user. Unfortunately, in an immersive virtual reality (VR) environment, a full per user calibration is not trivial and manual per user adjustment often leads to mini- or magnification of the scene. Therefore, we propose a novel per user calibration approach with optical see-through displays commonly used in augmented reality (AR). This calibration takes advantage of a geometric scheme based on 2D point - 3D line correspondences, which can be used intuitively by inexperienced users and requires less than a minute to complete. The required user interaction is based on taking aim at a distant target marker with a close marker, which ensures non-planar measurements covering a large area of the interaction space while also reducing the number of required measurements to five. We found the tendency that a calibrated view frustum reduced the average distance underestimation of users in an immersive VR environment, but even the correctly calibrated view frustum could not entirely compensate for the distance underestimation effects.     

Melt Crystallization of Ammonium Dinitramide (ADN) Investigated by Means of X-ray Diffraction

Ammonium dinitramide (ADN) is a promising oxidizing agent for solid rocket propellants. In situ XRD investigations of ADN and ADN suspensions have been performed in order to understand and refine the emulsion crystallization process for manufacturing spherical ADN particles (prills). The investigation revealed that the melt crystallization behavior depends on ADN quality, humidity, maximum temperature of temperature cycles, and suspension agents. Further investigations will focus on additives for controlling the mechanisms investigated, e.g., by seeding.