Cointegration in singular ARMA models

We consider the cointegration properties of singular ARMA processes integrated of order one. Such processes are necessarily cointegrated as opposed to the regular case. We show that in the left coprime case the cointegrating space only depends upon the autoregressive polynomial at one

Rheological and Mechanical Gradient Properties of Polyurethane Elastomers for 3D-Printing with Reactive Additives

Polyurethane (PU) elastomers with their broad range of strength and elasticity are ideal materials for additive manufacturing of shapes with gradients of mechanical properties. By adjusting the mixing ratio of different polyurethane reactants during 3D-printing it is possible to change the mechanical properties. However, to guarantee intra- and inter-layer adhesion, it is essential to know the reaction kinetics of the polyurethane reaction, and to be able to influence the reaction speed in a wide range. In this study, the effect of adding three different catalysts and two inhibitors to the reaction of polyurethane elastomers were studied by comparing the time of crossover points between storage and loss modulus G′ and G′′ from time sweep tests of small amplitude oscillatory shear at 30°C. The time of crossover points is reduced with the increasing amount of catalysts, but only the reaction time with one inhibitor is significantly delayed. The reaction time of 90% NCO group conversion calculated from the FTIR-spectrum also demonstrates the kinetics of samples with different catalysts. In addition, the relation between the conversion as determined from FTIR spectroscopy and the mechanical properties of the materials was established. Based on these results, it is possible to select optimized catalysts and inhibitors for polyurethane 3D-printing of materials with gradients of mechanical properties.DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Developing and validating an English version of the meCUE questionnaire for measuring user experience

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Based on the Component model of User Experience (CUE), a standardized questionnaire (meCUE) was developed measuring key aspects of user experience (UX) for interactive products. The questionnaire consists of 34 items and covers four components: product perceptions (usefulness, usability, visual aesthetics, status, commitment), user emotions (positive, negative), consequences of usage (intention to use, product loyalty), and overall judgment. The modules were separately validated in a series of studies. Therefore, meCUE can be easily adapted to specific research goals by simply choosing those modules which are required. The original German questionnaire was translated into an English version that was validated in an online study. Fifty-eight native English speakers assessed a wide variety of interactive products, such as cell phones, digital cameras, PCs, laptops, tablets, software and mobile applications. Results show that the English version reliably assesses the key components of UX and that the internal consistency of its scales is high.DFG, GRK 1013, Prospektive Gestaltung von Mensch-Technik-Interaktion (prometei

Arbuscular mycorrhizas in phosphate-polluted soil: interrelations between root colonization and nitrogen

To investigate whether arbuscular mycorrhizal fungi (AMF) – abundant in a phosphate-polluted but nitrogen-poor field site – improve plant N nutrition, we carried out a two-factorial experiment, including N fertilization and fungicide treatment. Percentage of root length colonized (% RLC) by AMF and tissue element concentrations were determined for four resident plant species. Furthermore, soil nutrient levels and N effects on aboveground biomass of individual species were measured. Nitrogen fertilization lowered % RLC by AMF of Artemisia vulgaris L., Picris hieracioides L. and Poa compressa L., but not of Bromus japonicus Thunb. This – together with positive N addition effects on N status, N:P-ratio and aboveground biomass of most species – suggested that plants are mycorrhizal because of N deficiency. Fungicide treatment, which reduced % RLC in all species, resulted in lower N concentrations in A. vulgaris and P. hieracioides, a higher N concentration in P. compressa, and did not consistently affect N status of B. japonicus. Evidently, AMF had an influence on the N nutrition of plants in this P-rich soil; however – potentially due to differences in their mycorrhizal responsiveness – not all species seemed to benefit froma mycorrhiza-mediated N uptake and accordingly, N distribution

Modeling elongational viscosity of polystyrene Pom-Pom/linear and Pom-Pom/star blends

The elongational rheology of blends of a polystyrene (PS) Pom-Pom with two linear polystyrenes was recently reported by Hirschberg et al. (J. Rheol. 2023, 67:403–415). The Pom-Pom PS280k-2x22-22k with a self-entangled backbone (M$_{w,bb}$ = 280 kg/mol) and 22 entangled sidearms (M$_{w,a}$ = 22 kg/mol) at each of the two branch points was blended at weight fractions from 75 to 2 wt% with two linear polystyrenes (PS) having M$_w$ of 43 kg/mol (PS43k) and 90 kg/mol (PS90k), respectively. While the pure Pom-Pom shows strong strain hardening in elongational flow (SHF > 100), strain hardening (SHF > 10) is still observed in Pom-Pom/linear blends containing only 2 wt% of Pom-Pom. The elongational start-up viscosities of the blends with Pom-Pom weight fractions above 10 wt% are well described by the Molecular Stress Function (MSF) model, however, requiring two nonlinear fit parameters. Here we show that quantitative and parameter-free modeling of the elongational viscosity data is possible by the Hierarchical Multi-mode Molecular Stress Function (HMMSF) model based on the concepts of hierarchical relaxation and dynamic dilution. In addition, we investigated the elongational viscosity of a blend consisting of 20 wt% Pom-Pom PS280k-2x22-22k and 80 wt% of a PS star with 11 arms of M$_{w,a}$ = 25 kg/mol having a similar span molecular weight as PS43k and similar M$_{w,a}$ as the Pom-Pom. This work might open up possibilities toward polymer upcycling of less-defined polymers by adding a polymer with optimized topology to gain the intended strain hardening, e.g., for film blowing applications

Spectroscopic database for TROPOMI/Sentinel-5P: CO and H2O at 2.3μm

The TROPOspheric Monitoring Instrument (TROPOMI) aboard the European Space Agency's Copernicus Sentinel-5 Precursor satellite, to be launched this year, mandates high-accuracy spectral reference data for CO and H2O in the 2.3μm region [1]. We present measurements of absorption line parameters for H2O and for the 2-0 rovibrational band of CO to be used in TROPOMI atmospheric retrievals. The experiments were carried out on a Bruker IFS 125HR Fourier transform spectrometer and a multispectrum fitting software developed at DLR was used for parameter retrieval [2] using the Hartmann-Tran-Profile [3,4]. In the case of carbon monoxide, we report line intensities, air-broadening and -shift parameters for lines of the 2-0 rovibrational band, which serve as a useful validation of the HITRAN2012 spectral database [5] while our analysis of Dicke narrowing, speed dependence and Rosenkranz line mixing emphasizes the importance of modern line shape functions. Comparisons with previous studies of these non-Voigt parameters (e.g. [6]) show good agreement. As for H2O, spectral parameters were measured in the 4190cm-1-4340cm-1 spectral range. Comparisons of measured line intensities of the ν3 band show remarkable agreement (<1.5% deviation on average) with ab initio values [7,8] and we will present air-broadening, -narrowing and -shift parameters together with their temperature dependences. References [1] J.P. Veefkind et al, Remote Sensing of Environment 120, 70 (2012) [2] J. Loos et al, 13th HITRAN database conference, 2014 (doi: 10.5281/zenodo.11156) [3] N.H. Ngo et al, JQSRT 129, 89 (2013) [4] N.H. Ngo et al, JQSRT 134, 105 (2014) [5] L.S. Rothman et al, JQSRT 130, 4 (2013) [6] V.M. Devi et al, JQSRT 113, 1013 (2012) [7] L. Lodi et al, J Chem Phys 135, 034113 (2011) [8] J. Tennyson, University College London, Private communicatio

Modeling elongational viscosity and brittle fracture of 10 polystyrene Pom-Poms by the hierarchical molecular stress function model

A Pom-Pom polymer with qa side chains of molecular weight Mw,a at both ends of a backbone chain of molecular weight Mw,b is the simplest branched polymer topology. Ten nearly monodisperse polystyrene Pom-Pom systems synthesized via an optimized anionic polymerization and a grafting-onto method with Mw,b of 100 to 400 kg/mol, Mw,a of 9 to 50 kg/mol, and qa between 9 and 22 are considered. We analyze the elongational rheology of the Pom-Poms by use of the hierarchical multi-mode molecular stress function (HMMSF) model, which has been shown to predict the elongational viscosity of linear and long-chain branched (LCB) polymer melts based exclusively on the linear-viscoelastic characterization and a single material parameter, the so-called dilution modulus GD. For the Pom-Poms considered here, we show that GD can be identified with the plateau modulus G0N=GD, and the modeling of the elongational viscosity of the Pom-Poms does therefore not require any fitting parameter but is fully determined by the linear-viscoelastic characterization of the melts. Due to the high strain hardening of the Pom-Poms, brittle fracture is observed at higher strains and strain rates, which is well described by the entropic fracture criterion