Ultrafast spectroscopy is used to study essential characteristics of solid-state materials. We use ultrafast techniques to study semiconductors at THz frequencies, as well as demonstrate new single-shot measurement techniques. The future of electronics is in the THz regime. We study a crucial characteristic of semiconductors used in devices: the critical field at which the material becomes conductive. GaAs is a promising semiconductor for high-speed devices, and we use enhanced THz electric fields to measure the critical fields at 0.7, 0.9, 1.1, and 1.5 THz frequencies. Single-shot spectroscopy is a technique used to measure ultrafast time scale laser pulses. We show that a new, optical-fiber-based single-shot technique can map out the electric field of THz pulses. Also, we show two variants on this single-shot theme that can be used to measure ultrafast signals. We compare a classic pump-probe measurement to two types of single-shot measurements that use either a spectrometer or a 3 km fiber optic cable and oscilloscope, and we discuss important considerations to recovering the sample response.

Abstract This thesis studies the long-term evolution of the photospheric magnetic field using surface flux transport simulations. The photospheric magnetic field and magnetic activity are tightly connected to space weather, and affect the whole heliosphere including the Earth. However, due to a lack of reliable observations our understanding of the long-term evolution of the photospheric magnetic field is still poor. Surface flux transport models, which are capable of simulating the evolution of the whole surface field from observations of solar activity, can be used to study the field in times when direct observations are not available. In this thesis we validate our surface flux transport model, optimize its parameters and test its sensitivity to uncertainties in parameter values and input data. We find a need to extend the model with a decay term to properly model the deep and long minimum between solar cycles 23 and 24, and simulate the photospheric magnetic field of cycles 21–24 using magnetographic observations as input. We also study consequences of hemispherically asymmetric activity, and show that activity in one hemisphere is enough to maintain polar fields in both hemispheres through cross-equatorial flow of magnetic flux. We develop a new method to reconstruct active regions from calcium K line and sunspot polarity observations. We show that this reconstruction is able to accurately capture the correct axial dipole moment of active regions. We study the axial dipole moments of observed active regions and find that a significant fraction of them have a sign opposite to the sign expected from Hale’s and Joy’s laws, proving that the new reconstruction method has an advantage over existing methods that rely on Hale’s and Joy’s laws to define polarities. We show one example of a long simulation covering solar cycles 15–21, demonstrating that using the active region reconstruction and surface flux transport model presented in this thesis it is possible to simulate the large-scale evolution of the photospheric magnetic field over the past century. / Original papers The original publications are not included in the electronic version of the dissertation. Virtanen, I. O. I., Virtanen, I. I., Pevtsov, A. A., Yeates, A., & Mursula, K. (2017). Reconstructing solar magnetic fields from historical observations. II. Testing the surface flux transport model. Astronomy & Astrophysics, 604, A8. https://doi.org/10.1051/0004-6361/201730415 http://jultika.oulu.fi/Record/nbnfi-fe2017103050356 Virtanen, I. O. I., Virtanen, I. I., Pevtsov, A. A., & Mursula, K. (2018). Reconstructing solar magnetic fields from historical observations. III. Activity in one hemisphere is sufficient to cause polar field reversals in both hemispheres. Astronomy & Astrophysics, 616, A134. https://doi.org/10.1051/0004-6361/201732323 http://jultika.oulu.fi/Record/nbnfi-fe201902205813 Virtanen, I. O. I., Virtanen, I. I., Pevtsov, A. A., Bertello, L., Yeates, A., & Mursula, K. (2019). Reconstructing solar magnetic fields from historical observations. IV. Testing the reconstruction method. Astronomy & Astrophysics, 627, A11. https://doi.org/10.1051/0004-6361/201935606 http://jultika.oulu.fi/Record/nbnfi-fe2019091828628 Virtanen, I. O. I., Virtanen, I. I., Pevtsov, A. A., & Mursula, K. (2019) Axial dipole moment of solar active regions in cycles 21-24. Manuscript.

My dissertation focuses on changes in health-related behavior in react to information-based intervention. The first chapter analyzes the results of a field experiment to investigate the effects of comparative information on the daily number of steps taken of adults. The second chapter further explores the effects using qualitative analysis. The third chapter intends to offer explanations in the mechanisms of the results from the first chapter. My first chapter uncovers how patterns in the daily number of steps of adults are affected by information that compares one with unknown peers. I conducted a field experiment that used fitness trackers to collect daily and minute-by-minute data on the total number of steps an individual takes in a day. Participants were randomized into a group that was provided with comparison information and a group that did not receive such information. I examined whether individuals in the two groups behaved differently during and after the intervention period. I find no clear evidence of an aggregate impact of social norms on the daily number of steps taken. However, I find individuals who are not overweight or nor married or cohabiting are more likely to be influenced by social norms. Greater treatment effects are found among individuals whose number of steps that are at the tails of the distribution curve. My second chapter reports the results of the textual data from the survey in the field experiment. I present dominant themes that emerged from answers to the open-ended essay questions in the survey. The results support that health concern, body image, appearance, psychological factors, peers and friends are major motives for being physically active. For participation in the study specifically, text messages that contain comparative information produced some improvement of the exercise level. However, participants also requested more interactions with peers, additional information provision, rewards for reaching goals. The results imply external incentives play a smaller role in promoting daily number of steps. In the third chapter, I conduct a survey experimentation to test the effectiveness of informing descriptive social norms and types of text messages in predictions about health-related behaviors. First, I investigate if errors in beliefs about activity levels exist and I find no evidence of over- or under-confidence in one’s own activity levels. Further analysis provide preliminary evidence of negative effects of informedness in predictions about one’s own behavior. However, the intention-to-treat effects of comparative information are unclear. The data provide evidence in favor of the correlation between first-order personal beliefs, not higher-order normative beliefs, in predicting an increase number of steps taken in response to intervention with text messages.

While various forms of teachers' habitus have been described in education studies, little consideration has so far been given to their interaction with fields in schools. This article draws on Bourdieu's theory and related concepts of field, habitus, capital and doxa to explore types of teacher professionalism, especially in Austrian secondary schools where innovative measures and reforms have been introduced. By combining a model of teaching profession with a Bourdieu-based analysis in the interpretation of 70 interviews with secondary school teachers, we show that a double field structure has emerged in some schools, where a field of traditional teaching competes with one of new professional field teaching. We argue that further initiatives will be needed from the field of education policy and other forces in society to stabilise the field of new professional teaching. This article illustrates the dynamic interrelationship between professional habitus and conflicting fields in one particular school.

This study however is confined to the Quarter-mile Intermediate Hurdles, as we know it today, an event for which, besides having a great deal of technical knowledge the participant must also be a highly trained individual. Even in Greek times, though, the individuals would train themselves hard in order to be better equipped to face the task which was in front of them. This, however, is the only similarity which exists between ancient Greek athletes and the modern day conception of the Quarter-mile Hurdles.

The Kapitza-Dirac effect is similar to the canonical experiment on diffraction of electrons through slits in an opaque screen, except that the diffraction grating has been replaced by a standing wave of light. Remarkably, incident electrons are diffracted by the standing light wave almost as if by a standard diffraction grating. Only recently has this effect been confirmed experimentally in this form [1], although it was originally predicted by Kapitza and Dirac almost 70 years ago. This paper examines the relativistic effects involved in this phenomena using the formalism of quantum field theory.

acase@tulane.edu / Ever since the successful isolation of graphene, plenty of researches have been pursued to study fundamental physics in low-dimensional van der Waals materials, referred to as materials with the existence of out of plane vdW force. Not only graphene but also many other novel vdW materials start to emerge and play important roles in quantum physics. Due to the highly preserved crystal quality of the nanostructures achieved by micromechanical exfoliation, a variety of new phenomenon have been discovered in these novel materials. This dissertation focuses on the discovery and electronic properties study of new vdW materials both in 2D and 1D systems. Semiconducting transition metal dichalcogenides with layered structure have been viewed as the promising channel materials for field-effect transistors (FETs) in modern electronics. To characterize the performance, we have fabricated FETs based on multilayer WS2 thin crystals. By using gold as the contact metal and varying the thickness of the crystal, high-performance FETs with on/off ratio of 108 and mobility up to 234 cm2V-1s-1 at room temperature have been realized. The high performance is associated with the minimized Schottky barrier and a shallow impurity level below the conduction band. Elementary substance and binary compound crystals have limited members belong to 2D or 1D family. Thus, expanding the research to ternary compound materials is necessary. In this regard, we focused on a novel ternary compound 2D material Nb3SiTe6 and studied its magneto-transport. We have discovered that by using such a high crystalline 2D metal, we could study the inelastic electron-phonon (e-ph) interactions involved with reducing dimensions. From 3D bulk to 2D films with a rigid substrate, the weak antilocalization (WAL) signature is gradually enhanced according to our magnetoresistance (MR) measurements. Systematic studies of the temperature dependence of the dephasing rate in the crystal with various thicknesses suggest the suppression of electron-phonon interaction due to quantum confinement of the phonon spectrum. Our work shows great consistency with the long-standing predicted theory. We have successfully expanded the mechanical exfoliation method to 1D material group. As demonstrated by semiconducting quasi-1D materials, Ta2Pd3Se8 (TPdS) and Ta2Pt3Se8 (TPtS), the external force can efficiently break the weak vdW interactions between ribbons. In our work, we have produced ultrathin 1D TPdS and TPtS nanowires, and fabricated 1D FETs showing p-type and n-type transistor behavior respectively. Moreover, we have successfully built the functional logic NOT gate using these two different 1D FETs. / 1 / Xue Liu

The diffeomorphism field is introduced to the physics literature in [1] where it arises as a background field coupled to Polyakov’s quantum gravity in two dimensions, where Einstein’s gravity is trivial. Moreover, it is seen in many ways as the gravitational analog of the Yang-Mills field. This raises the question of whether the diffeomorphism field exists in higher dimensions, playing an essential role in gravity either by supplementing Einstein’s theory or by modifying it. With this motivation, several distinct theories governing the dynamics of the diffeomorphism field have been constructed and developed by mimicking the construction of the Yang-Mills theory from the Kac-Moody algebra. This analogy, however, is not perfect and there are many subtleties and difficulties encountered. This thesis constitutes a further development. The previously proposed theories are carefully examined; certain subtleties and problems in them have been discovered and made apparent. Some of these problems have been solved, and for others possible routes to follow have been laid down. Finally, other geometric approaches than the ones followed before are investigated.

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