Cobalt dotiertes ZnO als verdünnter magnetischer Halbleiter

Verdünnte magnetische Halbleiter (DMS) sind technologisch vielversprechende Materialien mit sowohl ferromagnetischen als auch halbleitenden Eigenschaften. Sie gehören zu den entscheidenden Verbindungen bei der Entwicklung neuartiger Spintronikanwendungen. Bisher scheiterte der technologische Einsatz jedoch daran, dass die Curie Temperatur der meisten magnetischen Halbleiter viel zu niedrig ist. Neue Verbindungen auf Basis von ZnO wie Zn1-xCoxO sollen jedoch Ferromagnetismus oberhalb von Raumtemperatur zeigen. Die theoretischen Grundlagen der magnetischen Wechselwirkungen sind jedoch nicht verstanden und erfordern daher umfangreiche experimentelle Untersuchungen. Im Rahmen dieser Arbeit wurden dünne Filme aus Zn0.95Co0.05O mittels Laserablation hergestellt und bezüglich ihrer magnetischen, elektrischen und strukturellen Eigenschaften untersucht, mit dem Ziel den Ferromagnetismus in diesem Material besser zu verstehen. Dabei kamen verschiedene experimentelle Methoden zum Einsatz: wie Magnetometrie, Röntgendiffraktometrie, Magnetischer Röntgenzirkulardichroismus (XMCD), Elektronenspinresonanz sowie magnetoelektrische Transportmessungen. Bei entsprechend defektfördernden Herstellungsbedingungen zeigen die Proben klare ferromagnetische Eigenschaften oberhalb von Raumtemperatur mit einer Sättigungsmagnetisierung von ca. 2 Bohr Magneton / Co sowie einer Remanenz von bis zu 90%. Elektrische Transportmessungen zeigen zudem einen deutlichen Magnetowiderstand sowie einen anomalen Hall Effekt. Letzterer steigt mit der Probenmagnetisierung und spricht für intrinsischen Ferromagnetismus sowie eine geringe Spinpolarisation. Da der Ferromagnetismus mit höherer Ladungsträgerdichte jedoch verschwindet, ist eine ferromagnetische Wechselwirkung über die Leitungselektronen auszuschließen. Eine genauere Auswertung der magnetoelektrischen Messdaten deutet zudem auf ein leitendes Störstellenband hin, das unter Umständen selbst spinpolarisiert ist. Vieles spricht somit dafür, dass die ferromagnetische Ordnung über magnetische Polaronen zustande kommt. Einige strukturelle und magnetometrische Ergebnisse sowie Elektronenspinresonanzmessungen deuten zudem auf metallische Ausscheidungen in Form von Cobalt Clustern hin, die einen zusätzlichen extrinsischen ferromagnetischen Beitrag liefern, der deutlich größer sein könnte als der intrinsische. Überraschenderweise zeigen XMCD Messungen jedoch, dass Cobalt überhaupt nicht am Ferromagnetismus beteiligt ist. Insgesamt gibt es Anzeichen, dass magnetische Defekte eine entscheidende Rolle hinsichtlich des Magnetismus in Zn0.95Co0.05O spielen.

Studium hochkomplexer atomarer Spektren mittels Methoden der Laserresonanzionisation

In dieser Arbeit wurden umfangreiche laserspektroskopische Studien mit dem Zielrneines verbesserten Verständnisses höchst komplexer Spektren der Lanthanide und Aktinide durchgeführt. Einen Schwerpunkt bildete die Bestimmung bisher nicht oder mit unbefriedigender Genauigkeit bekannter erster Ionisationspotentiale für diese Elemente.rnHierzu wurden drei unterschiedliche experimentelle Methoden eingesetzt. Die Bestimmung des Ionisationspotentiales aus Rydbergserien wurde an den Beispielen Eisen, Mangan und Kobalt mit gemessenen Werten von IPFe = 63737, 6 ± 0, 2stat ± 0, 1syst cm−1, IPMn = 59959, 6 ± 0, 4 cm−1 beziehungsweise IPCo = 63564, 77 ± 0, 12 cm−1 zunächst erfolgreich erprobt. Die bestehenden Literaturwerte konnten in diesen Fällen bestätigt werden und bei Eisen und Kobalt die Genauigkeit etwa um einen Faktor drei bzw. acht verbessert werden. Im Falle der Lanthaniden und Aktiniden jedoch ist die Komplexität der Spektren derart hoch, dass Rydbergserien in einer Vielzahl weiterer Zustände beliebiger Konfiguration nicht oder kaum identifiziert werden können.rnUm dennoch das Ionisationspotential bestimmen zu können, wurde die verzögerte, gepulste Feldionisation wie auch das Verfahren der Isolated Core Excitation am Beispiel des Dysprosiums erprobt. Aus den so identifizierten Rydbergserien konnten Werte von IPFeld = 47899 ± 3 cm−1 beziehungsweise IPICE = 47900, 4 ± 1, 4 cm−1 bestimmt werden. Als komplementärer Ansatz, der auf ein möglichst reichhaltiges Spektrum in der Nähe des Ionisationspotentiales angewiesen ist, wurde zusätzlich die Sattelpunktsmethode erfolgreich eingesetzt. Das Ionisationspotential des Dysprosium wurde damit zu IPDy = 47901, 8±0, 3 cm−1 bestimmt, wobei am Samarium, dessen Ionisationspotential aus der Literatur mit höchster Genauigkeit bekannt ist, bestätigt werden konnte, dassrnauftretende systematische Fehler kleiner als 1 cm−1 sind. Das bisher sehr ungenau bekannte Ionisationspotential des Praseodyms wurde schließlich zu IPPr = 44120, 0 ± 0, 6 cm−1 gemessen. Hiermit wird der bisherige Literaturwert bei einer Verbesserung der Genauigkeit um zwei Größenordnungen um etwa 50 cm−1 nach oben korrigiert. Aus der Systematik der Ionisationspotentiale der Lanthaniden konnte schließlich das Ionisationspotential des radioaktiven Promethiums mit IPPm = 44985 ± 140 cm−1 vorhergesagt werden. Abschließend wurde die Laserresonanzionisation des Elements Protactinium demonstriertrnund das Ionisationspotential erstmals experimentell bestimmt. Ein Wert vonrn49000±110 cm−1 konnte aus dem charakteristischen Verhalten verschiedener Anregungsschemata gefolgert werden. Dieser Wert liegt etwa 1500 cm−1 höher als der bisherige Literaturwert, theoretische Vorhersagen weichen ebenfalls stark ab. Beide Abweichungen können über eine Betrachtung der Systematik der Ionisationspotentiale in der Aktinidenreihe hervorragend verstanden werden.

Messung dynamischer Prozesse in der Nähe von Grenzflächen mit Hilfe neu entwickelter Lichtstreumethoden

Die vorliegende Arbeit behandelt die Entwicklung und Erprobung zweier neuer dynamischer Lichtstreumethoden: Die Resonanz verstärkte Lichtstreuung (REDLS: resonance enhanced dynamic light scattering) und die Wellenleiter verstärkte Lichtstreuung (WEDLS: waveguide enhanced dynamic light scattering). Beide Methoden verwenden eine Kombination aus evaneszenten Wellen und dynamischer Lichtstreuung: Bei der REDLS-Technik wird das evaneszentes Feld eines Oberflächenplasmons verwendet, bei der WEDLS-Technik handelt es sich um das evaneszente Feld von Metallfilm verstärkten Leckwellenleitermoden. Die neuen Methoden liefern Informationen über die Dynamik an Grenzflächen über ein breites Zeitfenster (einige Nanosekunden bis hin zu mehreren Sekunden) mit einer räumlichen Auflösung im sub-Mikrometerbereich. Sie erweitern somit das Gebiet der dynamischen Lichtstreuung in evaneszenter Geometrie, bei dem bislang nur die evanescent wave dynamic light scattering (EWDLS) - Technik zur Verfügung stand. Bei der EWDLS-Technik wird das evaneszente Feld der Totalreflexion als kohärenter Lichtstrahl für die dynamische Lichtstreuung verwendet. Ein Vergleich mit der EWDLS-Technik zeigt ein stark erhöhtes Signal/Rausch-Verhältnis bei den neu entwickelten Techniken aufgrund der resonanten Anregung. Zusätzlich ist es sowohl bei der REDLS- als auch bei der WEDLS-Technik möglich Grenzflächenmodifikationen und damit z.B. Adsorptionsprozesse zu detektieren. Der Einfluss einer Grenzfläche auf die Diffusion von PS-Latex-Partikeln wurde untersucht. Die Grenzfläche bestand im Fall der REDLS-Technik aus Gold, bei der WEDLS-Technik aus PMMA. Die Funktionsweise und die Gültigkeit der neu entwickelten Techniken wurde mit Hilfe von PS-Latex-Partikeln mit hydrodynamischen Radien von R =11nm bis hin zu R=204nm demonstriert.

Femtosecond laser-based investigations of magnetic circular dichroism in near-threshold photoemission

During the last decades magnetic circular dichroism (MCD) has attracted much interest and evolved into various experimental methods for the investigation of magnetic thin films. For example, synchrotron-based X-ray magnetic circular dichroism (XMCD) displays the absolute values of spin and orbital magnetic moments. It thereby benefits from large asymmetry values of more than 30% due to the excitation of atomic core-levels. Similarly large values are also expected for threshold photoemission magnetic circular dichroism (TPMCD). Using lasers with photon energies in the range of the sample work function this method gives access to the occupied electronic structure close to the Fermi level. However, except for the case of Ni(001) there exist only few studies on TPMCD moreover revealing much smaller asymmetries than XMCD-measurements. Also the basic physical mechanisms of TPMCD are not satisfactorily understood. In this work we therefore investigate TPMCD in one- and two-photon photoemission (1PPE and 2PPE) for ferromagnetic Heusler alloys and ultrathin Co films using ultrashort pulsed laser light. The observed dichroism is explained by a non-conventional photoemission model using spin-resolved band-structure calculations and linear response theory. For the two Heusler alloys Ni2MnGa and Co2FeSi we give first evidence of TPMCD in the regime of two-photon photoemission. Systematic investigations concerning general properties of TPMCD in 1PPE and 2PPE are carried out at ultrathin Co films grown on Pt(111). Here, photon-energy dependent measurements reveal asymmetries of 1.9% in 1PPE and 11.7% in 2PPE. TPMCD measurements at decreased work function even yield larger asymmetries of 6.2% (1PPE) and 17% (2PPE), respectively. This demonstrates that enlarged asymmetries are also attainable for the TPMCD effect on Co(111). Furthermore, we find that the TPMCD asymmetry is bulk-sensitive for 1PPE and 2PPE. This means that the basic mechanism leading to the observed dichroism must be connected to Co bulk properties; surface effects do not play a crucial role. Finally, the enhanced TPMCD asymmetries in 2PPE compared to the 1PPE case are traced back to the dominant influence of the first excitation step and the existence of a real intermediate state. The observed TPMCD asymmetries cannot be interpreted by conventional photoemission theory which only considers direct interband transitions in the direction of observation (Γ-L). For Co(111), these transitions lead to evanescent final states. The excitation to such states, however, is incompatible with the measured bulk-sensitivity of the asymmetry. Therefore, we generalize this model by proposing the TPMCD signal to arise mostly from direct interband transitions in crystallographic directions other than (Γ-L). The necessary additional momentum transfer to the excited electrons is most probably provided by electron-phonon or -magnon scattering processes. Corresponding calculations on the basis of this model are in reasonable agreement with the experimental results so that this approach represents a promising tool for a quantitative description of the TPMCD effect. The present findings encourage an implementation of our experimental technique to time- and spatially-resolved photoemission electron microscopy, thereby enabling a real time imaging of magnetization dynamics of single excited states in a ferromagnetic material on a femtosecond timescale.

Experiments on Pro-Sociality and Environmental Issues

The thesis comprises three essays that use experimental methods, one about other-regarding motivations in economic behavior and the others on pro-social behavior in two environmental economics problems. The first chapter studies how the expectations of the others and the concern to maintain a balance between effort exerted and rewards obtained interact in shaping the behavior in a modified dictator game. We find that dictators condition their choices on recipients' expectations only when there is a high probability that the the recipient will not be compensated for her effort. Otherwise, dictators tend to balance the efforts and rewards of the recipients, irrespective of the recipients' expectations. In the second chapter, I investigate the problem of local opposition to large public projects (e.g. landfills, incinerators, etc.). In particular, the experiment shows how the uncertainty about the project's quality makes the community living in the host site skeptical about the project. I also test whether side-transfers and costly information disclosure can help to increase the efficiency. Both tools succesfully make the host more willing to accept the project, but they lead to the realization of different types of projects. The last chapter is an experiment on climate negotiations. To avoid the global warming, countries are called to cooperate in the abatement of their emissions. We study whether the dynamic aspect of the climate change makes cooperation across countries behaviorally more difficult. We also consider inequality across countries as a possible factor that hinders international cooperation.

Advanced polymeric materials for applications in technical equipment for snow sports

The thesis is divided in three chapters, each one covering one topic. Initially, the thermo-mechanical and impact properties of materials used for back protectors have been analysed. Dynamical mechanical analysis (DMTA) has shown that materials used for soft-shell protectors present frequency-sensitive properties. Furthermore, through impact tests, the shock absorbing characteristics of the materials have been investigated proving the differences between soft and hard-shell protectors; moreover it has been demonstrated that the materials used for soft-shell protectors maintain their protective properties after multi-impacts. The second chapter covers the effect of the visco-elastic properties of the thermoplastic polymers on the flexural and rebound behaviours of ski boots. DMTA analysis on the materials and flexural and rebound testing on the boots have been performed. A comparison of the results highlighted a correlation between the visco-elastic properties and the flexural and rebound behaviour of ski boots. The same experimental methods have been used to investigate the influence of the design on the flexural and rebound behaviours. Finally in the third chapter the thermoplastic materials employed for the construction of ski boots soles have been characterized in terms of chemical composition, hardness, crystallinity, surface roughness and coefficient of friction (COF). The results showed a relation between material hardness and grip, in particular softer materials provide more grip with respect to harder materials. On the contrary, the surface roughness has a negative effect on friction because of the decrease in contact area. The measure of grip on inclined wet surfaces showed again a relation between hardness and grip. The performance ranking of the different materials has been the same for the COF and for the slip angle tests, indicating that COF can be used as a parameter for the choice of the optimal material to be used for the soles of ski boots.

Dotierte Nanographenstreifen mit definierten Randstrukturen

Die in der vorliegenden Dissertation entwickelten organochemischen Protokolle und Konzepte erweitern die Bottom-Up-Synthese von atompräzisen Nanographenstreifen (GNR) um zwei fundamentale Bereiche. Zum einen die Dotierung der halbleitenden GNR mit Schwefel oder Stickstoffatomen und zum anderen ein Protokoll für eine lösungsbasierte Synthese von stickstoffdotierten Zickzack-Streifen.rnDie Dotierung von GNR beinhaltet die Synthese von monomeren Bausteinen bei denen, im Gegensatz zu ihren reinen Kohlenstoffhomologen, definierte Positionen am Rand mit zwei oder vier Stickstoff- beziehungsweise zwei Schwefelatomen ersetzt wurden. Die Synthese atompräziser GNR konnte mit verschiedenen experimentellen Methoden analysiert und anschaulich über STM visualisiert werden. Neben einer n-Dotierung gelang so auch erstmals eine Bottom-Up-Synthese von schwefeldotierten GNR. Eine mögliche Anwendung in der Nanoelektronik aufbauend auf dotierten GNR wurde bestätigt, indem durch Co-Polymerisation von stickstoffhaltigen mit reinen Kohlenstoffmonomeren Heteroschnittstellen zwischen dotierten und undotierten Bereichen hergestellt werden konnten. Solche Heteroschnittstellen sind fundamentale Grundlage von Dioden und damit Basis einer Vielzahl elektronischer Elemente wie Solarzellen oder Leuchtdioden.rnWährend für halbleitende GNR mit einer Armlehnen-Form ein breites Spektrum an organischen Syntheseprotokollen zur Verfügung stand, existierte zu Beginn dieser Arbeit keines für GNR mit Zickzack-Struktur. Innerhalb dieser Arbeit konnte eine Bottom-Up-Synthese zur Erschließung stickstoffdotierter GNR mit Zickzack-Randstruktur erarbeitet werden. Durch die Verwendung eines (2-Hydroxymethyl)phenylboronsäureesters werden Hydroxymethylsubsituenten entlang eines Polyphenylenrückgrats eingebaut, die nach Kondensation mit dem Stickstoffatom eine Zickzack-Kante ergeben. Innerhalb der synthetisierten Zielstrukturen kann das 9a-Azaphenalen als letztes, bislang nicht erschlossenes Isomer der Azaphenalene, als wiederkehrende Struktur, gefunden werden. Die Reaktivität der Zickzackkante konnte zudem zum Aufbau einer Vielzahl bislang unzugänglicher, polycyclischer Heteroaromaten über 1,3-dipolare Addition dieses polycyclischen Azomethin Ylides (PAMY) genutzt werden.rn

Emission cross sections for neutral xenon impacted by Xe+ and Xe2+

Ion impact emission cross sections for eleven transitions from the 5p56p configuration to the 5p56s configuration of neutral xenon occurring in the spectral region between 700 nm and 1000 nm have been measured experimentally. Collisions between both singly- and doublyionized xenon and neutral xenon have been studied. These cross sections are of primary use in the development of a spectrographic diagnostic for Hall effect thruster plasma. A detailed discussion of the experimental methods and the subsequent data reduction is included. The results are presented and the importance of these data for spectrographic emission models of Hall effect thruster plasmas is discussed.

Thickness measurement of dynamic thin liquid films generated by plug-annular flow in non-wetting microchannels

Surface tension forces are significant at millimeter length-scales, causing profoundly different flow morphologies in microchannels than in macroscale flows. The existence and morphology of thin liquid films is particularly relevant for predicting performance and operational stability of devices containing microscale two phase flows. Analytical, computational, and experimental methods previously employed in the study of thin liquid films are discussed. Thicknesses before and after a novel film morphology, referred to as a `shock,' are measured with a novel film thickness measurement technique that uses confocal microscopy. Film thicknesses predicted by previous work are compared to experimental results. Methods for increasing the accuracy of the confocal film thickness measurement technique are discussed.

DEVELOPMENT OF CONFOCAL IMAGING TECHNIQUES FOR PROBING INTERFACIAL DYNAMICS IN MICROSCALE, GAS-LIQUID, TWO-PHASE FLOW

Micro-scale, two-phase flow is found in a variety of devices such as Lab-on-a-chip, bio-chips, micro-heat exchangers, and fuel cells. Knowledge of the fluid behavior near the dynamic gas-liquid interface is required for developing accurate predictive models. Light is distorted near a curved gas-liquid interface preventing accurate measurement of interfacial shape and internal liquid velocities. This research focused on the development of experimental methods designed to isolate and probe dynamic liquid films and measure velocity fields near a moving gas-liquid interface. A high-speed, reflectance, swept-field confocal (RSFC) imaging system was developed for imaging near curved surfaces. Experimental studies of dynamic gas-liquid interface of micro-scale, two-phase flow were conducted in three phases. Dynamic liquid film thicknesses of segmented, two-phase flow were measured using the RSFC and compared to a classic film thickness deposition model. Flow fields near a steadily moving meniscus were measured using RSFC and particle tracking velocimetry. The RSFC provided high speed imaging near the menisci without distortion caused the gas-liquid interface. Finally, interfacial morphology for internal two-phase flow and droplet evaporation were measured using interferograms produced by the RSFC imaging technique. Each technique can be used independently or simultaneously when.

Predictive oncology: a review of multidisciplinary, multiscale in silico modeling linking phenotype, morphology and growth.

Empirical evidence and theoretical studies suggest that the phenotype, i.e., cellular- and molecular-scale dynamics, including proliferation rate and adhesiveness due to microenvironmental factors and gene expression that govern tumor growth and invasiveness, also determine gross tumor-scale morphology. It has been difficult to quantify the relative effect of these links on disease progression and prognosis using conventional clinical and experimental methods and observables. As a result, successful individualized treatment of highly malignant and invasive cancers, such as glioblastoma, via surgical resection and chemotherapy cannot be offered and outcomes are generally poor. What is needed is a deterministic, quantifiable method to enable understanding of the connections between phenotype and tumor morphology. Here, we critically assess advantages and disadvantages of recent computational modeling efforts (e.g., continuum, discrete, and cellular automata models) that have pursued this understanding. Based on this assessment, we review a multiscale, i.e., from the molecular to the gross tumor scale, mathematical and computational "first-principle" approach based on mass conservation and other physical laws, such as employed in reaction-diffusion systems. Model variables describe known characteristics of tumor behavior, and parameters and functional relationships across scales are informed from in vitro, in vivo and ex vivo biology. We review the feasibility of this methodology that, once coupled to tumor imaging and tumor biopsy or cell culture data, should enable prediction of tumor growth and therapy outcome through quantification of the relation between the underlying dynamics and morphological characteristics. In particular, morphologic stability analysis of this mathematical model reveals that tumor cell patterning at the tumor-host interface is regulated by cell proliferation, adhesion and other phenotypic characteristics: histopathology information of tumor boundary can be inputted to the mathematical model and used as a phenotype-diagnostic tool to predict collective and individual tumor cell invasion of surrounding tissue. This approach further provides a means to deterministically test effects of novel and hypothetical therapy strategies on tumor behavior.

Water–montmorillonite systems: Neutron scattering and tracer throughdiffusion studies

Designs for deep geological respositories of nuclear waste include bentonite as a hydraulic and chemisorption buffer material to protect the biosphere from leakage of radionuclides. Bentonite is chosen because it is a cheap, naturally occurring material with the required properties. It consists essentially of montmorillonite, a swelling clay mineral. Upon contact with groundwater such clays can seal the repository by incorporating water in the interlayers of their crystalline structure. The intercalated water exhibits significantly different properties to bulk water in the surrounding interparticle pores, such as lower diffusion coefficients (González Sánchez et. al. 2008). This doctoral thesis presents water distribution and diffusion behavior on various time and space scales in montmorillonite. Experimental results are presented for Na- and Cs-montmorillonite samples with a range of bulk dry densities (0.8 to 1.7 g/cm3). The experimental methods employed were neutron scattering (backscattering, diffraction, time-of-flight), adsorption measurements (water, nitrogen) and tracer-through diffusion. For the tracer experiments the samples were fully saturated via the liquid phase under volume-constrained conditions. In contrast, for the neutron scattering experiments, the samples were hydrated via the vapor phase and subsequently compacted, leaving a significant fraction of interparticle pores unfilled with water. Owing to these differences in saturation, the water contents of the samples for neutron scattering were characterized by gravimetry whereas those for the tracer experiments were obtained from the bulk dry density. The amount of surface water in interlayer pores could be successfully discriminated from the amount of bulk-like water in interparticle pores in Na- and Csmontmorillonite using neutron spectroscopy. For the first time in the literature, the distribution of water between these two pore environments was deciphered as a function of gravimetric water content. The amount was compared to a geometrical estimation of the amount of interlayer and interparticle water determined by neutron diffraction and adsorption measurements. The relative abundances of the 1 to 4 molecular water layers in the interlayer were determined from the area ratios of the (001)-diffraction peaks. Depending on the characterization method, different fractions of surface water and interlayer water were obtained. Only surface and interlayer water exists in amontmorillonite with water contents up to 0.18 g/g according to spectroscopic measurements and up to 0.32 g/g according to geometrical estimations, respectively. At higher water contents, bulk-like and interparticle water also exists. The amounts increase monotonically, but not linearly, from zero to 0.33 g/g for bulk-like water and to 0.43 g/g for interparticle water. It was found that water most likely redistributes between the surface and interlayer sites during the spectroscopic measurements and therefore the reported fraction is relevant only below about -10 ºC (Anderson, 1967). The redistribution effect can explain the discrepancy in fractions between the methods. In a novel approach the fractions of water in different pore environments were treated as a fixed parameter to derive local diffusion coefficients for water from quasielastic neutron scattering data, in particular for samples with high water contents. Local diffusion coefficients were obtained for the 1 to 4 molecular water layers in the interlayer of 0.5·10–9, 0.9·10–9, 1.5·10–9 and 1.4·10–9 m²/s, respectively, taking account of the different water fractions (molecular water layer, bulk-like water). The diffusive transport of 22Na and HTO through Na-montmorillonite was measured on the laboratory experimental scale (i.e. cm, days) by tracer through-diffusion experiments. We confirmed that diffusion of HTO is independent of the ionic strength of the external solution in contact with the clay sample but dependent on the bulk dry density. In contrast, the diffusion of 22Na was found to depend on both the ionic strength of the pore solution and on the bulk dry density. The ratio of the pore and surface diffusion could be experimentally determined for 22Na from the dependence of the diffusion coefficient on the ionic strength. Activation energies were derived from the temperaturedependent diffusion coefficients via the Arrhenius relation. In samples with high bulk dry density the activation energies are slightly higher than those of bulk water whereas in low density samples they are lower. The activation energies as a function of ionic strengths of the pore solutions are similar for 22Na and HTO. The facts that (i) the slope of the logarithmic effective diffusion coefficients as a function of the logarithmic ionic strength is less than unity for low bulk dry densities and (ii) two water populations can be observed for high gravimetric water contents (low bulk dry densities) support the interlayer and interparticle porosity model proposed by Glaus et al. (2007), Bourg et al. (2006, 2007) and Gimmi and Kosakowski (2011).

Using Factorial Surveys and Stated Choice Experiments to Investigate Discriminatory Attitudes and Preferences

Empirical research on discriminatory attitudes and behaviour grapples with the social undesirability of its object. In many studies using regular survey methods, estimates are biased, and the social context of discrimination is not taken into account. Several methods have been developed, especially to deal with the first problem. In this regard, the estimation of the ‘true value’ of discriminatory attitudes is at the centre of interest. However, methodological contributions focusing on the social context of attitude communication and discriminatory behaviour, as well as the correlation between both, are rare. We present two experimental methods which address those issues: factorial surveys and stated choice experiments. In a first study, the usefulness of factorial surveys is demonstrated with data on German anti-Semitism (N=279). We show that the rate of approval with anti-Semitic statements increases if (a) respondents are told that the majority of fellows agree with such statements, (b) the term “Jews” is replaced by the term “Israelis”, and (c) reference to the Holocaust is made. Apart from the main effects of these experimental factors, significant interaction effects regarding the political attitudes and social status of respondents are observed. In a second study, a stated choice experiment on the purchase of olive oil and tomatoes was conducted in Germany (N=440). We find that respondents prefer Italian and Dutch products (control treatment) compared to Israeli and Palestinian ones (discrimination treatments). There are no significant differences between preferences for a so called ‘Peace product’ (which is produced jointly by Israelis and Palestinians) and products from Italy as well as the Netherlands. Yet, taking discriminatory attitudes (anti-Semitic and anti-Arabic attitudes) into account, a strong correlation between those attitudes and stated behaviour (purchase of Israeli, Palestinian and jointly produced products) can be found. This adds support to the hypothesis that discriminatory attitudes hold behavioural consequences.

Understanding the Sharing Economy: The Role of Response to Negative Reviews in the Peer-To-Peer Accommodation Sharing Network?

Recognizing the potentially ruinous effect of negative reviews on the reputation of the hosts as well as a subjective nature of the travel experience judgements, peer-to-peer accommodation sharing plat-forms, like Airbnb, have readily embraced the “response” option, empowering hosts with the voice to challenge, deny or at least apologize for the subject of critique. However, the effects of different re-sponse strategies on trusting beliefs towards the host remain unclear. To fill this gap, this study focus-es on understanding the impact of different response strategies and review negativity on trusting be-liefs towards the host in peer-to-peer accommodation sharing setting utilizing experimental methods. Examination of two different contexts, varying in the controllability of the subject of complaint, re-veals that when the subject of complaint is controllable by a host, such strategies as confession / apol-ogy and denial can improve trusting beliefs towards the host. However, when the subject of criticism is beyond the control of the host, denial of the issue does not yield guest’s confidence in the host, where-as confession and excuse have positive influence on trusting beliefs.

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica

We present successful 81 Kr-Kr radiometric dating of ancient polarice. Krypton was extracted from the air bubbles in four∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The 81 Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean abso-lute age offset of 6±2.5 ka. Our experimental methods and sampling strategy are validated by (i) 85 Kr and 39 Ar analyses that show the samples to be free of modern air contamination and (ii)air content measurements that show the ice did not experience gas loss. We estimate the error in the 81 Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130–115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA 81Kr analysis requires a 40–80-kg ice sample; as sample requirements continue to decrease, 81 Kr dating of ice cores is a future possibility.