Superconducting Vortices in Half-Metals

When the impurity mean free path is short, only spin-polarized Cooper pairs which are non-locally and antisymmetrically correlated in time may exist in a half-metallic ferromagnet. As a consequence, the half-metal acts as an odd-frequency superconducting condensate. We demonstrate both analytically and numerically that quantum vortices can emerge in half-metals despite the complete absence of conventional superconducting correlations. Because these metals are conducting in only one spin band, we show that a circulating spin supercurrent accompanies these vortices. Moreover, we demonstrate that magnetic disorder at the interfaces with the superconductor influences the position at which the vortices nucleate. This insight can be used to help determine the effective interfacial misalignment angles for the magnetization in hybrid structures, since the vortex position is experimentally observable via STM-measurements. We also give a brief discussion regarding which superconducting order parameter to use for odd-frequency triplet Cooper pairs in the quasiclassical theory.Comment: 9 pages, 8 figure

Compressive Time Delay Estimation Using Interpolation

Time delay estimation has long been an active area of research. In this work, we show that compressive sensing with interpolation may be used to achieve good estimation precision while lowering the sampling frequency. We propose an Interpolating Band-Excluded Orthogonal Matching Pursuit algorithm that uses one of two interpolation functions to estimate the time delay parameter. The numerical results show that interpolation improves estimation precision and that compressive sensing provides an elegant tradeoff that may lower the required sampling frequency while still attaining a desired estimation performance.Comment: 5 pages, 2 figures, technical report supporting 1 page submission for GlobalSIP 201

Compressive Parameter Estimation for Sparse Translation-Invariant Signals Using Polar Interpolation

We propose new compressive parameter estimation algorithms that make use of polar interpolation to improve the estimator precision. Our work extends previous approaches involving polar interpolation for compressive parameter estimation in two aspects: (i) we extend the formulation from real non-negative amplitude parameters to arbitrary complex ones, and (ii) we allow for mismatch between the manifold described by the parameters and its polar approximation. To quantify the improvements afforded by the proposed extensions, we evaluate six algorithms for estimation of parameters in sparse translation-invariant signals, exemplified with the time delay estimation problem. The evaluation is based on three performance metrics: estimator precision, sampling rate and computational complexity. We use compressive sensing with all the algorithms to lower the necessary sampling rate and show that it is still possible to attain good estimation precision and keep the computational complexity low. Our numerical experiments show that the proposed algorithms outperform existing approaches that either leverage polynomial interpolation or are based on a conversion to a frequency-estimation problem followed by a super-resolution algorithm. The algorithms studied here provide various tradeoffs between computational complexity, estimation precision, and necessary sampling rate. The work shows that compressive sensing for the class of sparse translation-invariant signals allows for a decrease in sampling rate and that the use of polar interpolation increases the estimation precision.Comment: 13 pages, 5 figures, to appear in IEEE Transactions on Signal Processing; minor edits and correction

Reliable Identification of RFID Tags Using Multiple Independent Reader Sessions

Radio Frequency Identification (RFID) systems are gaining momentum in various applications of logistics, inventory, etc. A generic problem in such systems is to ensure that the RFID readers can reliably read a set of RFID tags, such that the probability of missing tags stays below an acceptable value. A tag may be missing (left unread) due to errors in the communication link towards the reader e.g. due to obstacles in the radio path. The present paper proposes techniques that use multiple reader sessions, during which the system of readers obtains a running estimate of the probability to have at least one tag missing. Based on such an estimate, it is decided whether an additional reader session is required. Two methods are proposed, they rely on the statistical independence of the tag reading errors across different reader sessions, which is a plausible assumption when e.g. each reader session is executed on different readers. The first method uses statistical relationships that are valid when the reader sessions are independent. The second method is obtained by modifying an existing capture-recapture estimator. The results show that, when the reader sessions are independent, the proposed mechanisms provide a good approximation to the probability of missing tags, such that the number of reader sessions made, meets the target specification. If the assumption of independence is violated, the estimators are still useful, but they should be corrected by a margin of additional reader sessions to ensure that the target probability of missing tags is met.Comment: Presented at IEEE RFID 2009 Conferenc

Safe Today, Tomorrow, and Together: A Dynamic Perspective on Team Psychological Safety

There is an increasing focus in organizations on building psychologically safe teams. This follows a large—and rapidly growing—body of research supporting the importance of team psychological safety for effective teamwork. Still, there is a lack of research on the dynamics of team psychological safety. This is somewhat surprising given the ever-changing nature of teams and leaves us with an incomplete understanding of team psychological safety. This dissertation makes several important contributions to the research field. Paper 1 provides a comprehensive overview of the temporal dynamics of team emergent states, of which team psychological safety is one. This literature review shows that team emergent states have no universal pattern, why team emergent states should be measured as emergent, why team emergent states arise, the consequences of temporal dynamics, and why studying the emergent element of these states matters. Overall, the paper raises awareness of the importance of taking the “emergent” in team emergent states seriously. In Paper 2, I explore the dynamic nature of team psychological safety. By studying teams from when they are established and over different time horizons, this paper reveals how temporally dynamic team psychological safety may indeed be and how its emergence and development relate to the practices of the team. Since team psychological safety may both wax and wane, time itself is neither sufficient nor necessarily positive. Instead, team psychological safety reveals itself as a perishable good. Where Papers 1 and 2 emphasize the temporal dynamics of team psychological safety, Paper 3 addresses the within-team dynamics—more specifically, how sharedness among team members (that is, team psychological safety climate strength) moderates the relationship between team psychological safety and team performance. Moreover, explorative analyses reveal how sharedness is not necessarily beneficial. In particular, when psychological safety is low, a safe team member among the unsafe may positively impact team performance. In sum, this thesis contributes to the research field by identifying the emergent nature of team emergent states in general and team psychological safety in particular and by revising the view of team psychological safety as necessarily being perceived similarly among team members. I discuss the theoretical contributions and practical implications of these findings. Keywords: team emergent states, team psychological safety, temporal dynamics, team psychological safety climate strength, team performanc

Barriers and facilitators to increasing work participation among people with moderate to severe mental illness

This thesis seeks to identify facilitators and barriers to obtaining employment for people in treatment for moderate to severe mental illness. Many people with mental illness wish to pursue life goals such as ordinary employment, and several studies have demonstrated the positive association between employment and physical and mental health. Even so, obtaining ordinary employment can be a challenge, which is demonstrated by high unemployment rates among people with moderate to severe mental illness. The current thesis bases most of its work on an effect evaluation of the vocational rehabilitation program Individual Placement and Support (IPS). IPS provides long-term, individualized follow-up through an IPS specialist, with the goal of obtaining competitive employment. Alhthough numerous international studies have proven IPS to be more effective than traditional forms of vocational rehabilitation, the trial described in this thesis was the first to investigate the effect of IPS in a Norwegian context. This context is characterized by a generous welfare system, which has many advantages, but may also create incentives to remain outside the workforce. It was therefore not given that IPS would be more effective than ordinary vocational services in this context. The effect evaluation did, however, prove it to be effective also in Norway. The work presented in the current thesis seeks to understand how the intervention works, and which factors influence employment for its target group. Paper 1 investigates the IPS implementation through a process evaluation, utilizing data from IPS service providers, fidelity reports, and participants. The study uses mixed methods, with an emphasis on the quantitative material. Results from paper 1 show that IPS was implemented successfully across the six pilot centers, as demonstrated by satisfactory fidelity scores during the project period. Fidelity scores did indicate implementation challenges related to employment contact, providing community-based services, and integration with health services, which was further elaborated on in interviews with IPS specialists. Participants were overall very satisfied with the intervention, and emphasized the important role of the IPS specialist. Moreover, participants found freedom of disclosure to be important for participation. Less than half of the participants regarded their illness as a barrier to participation in the intervention. Paper 2 investigates baseline-measured predictors for employment after 18 months, and whether group allocation (IPS vs TAU) moderates this effect. The study population consists of 327 participants from the IPS trial, and log binary regression analyses were conducted to investigate the research questions. Results indicate that while involuntary hospitalization is a strong negative predictor for employment at 18 months’ follow-up, directive emotional support and non-directive instrumental support positively predict employment. Self-reported measures of anxiety and depression, directive instrumental and non-directive emotional support, age, and education did not predict employment at 18 months in this study, supporting an inclusive approach to providing vocational rehabilitation to the target group. Paper 3 investigates the perspective of Norwegian workplaces and their assessment of fictive job candidates who either had a mental illness, a physical disability, or a cultural minority background. Results show that supervisors and employees in Norwegian workplaces were generally reluctant towards vignette characters with a mental illness in terms of hireability. However, respondents who reported to have previous work experience with a colleague resembling the vignette character in question, generally assessed this character more positively than those who did not have this experience. Main concerns regarding the characters with a mental illness were social interaction and increased workload for colleagues. The paper concludes that job candidates with some kind of health issue are still likely to be underestimated in the labor market. In conclusion, the findings of the PhD thesis highlight specific barriers and facilitators operating on different levels, to work participation for people with moderate to severe mental illness. It provides avenues for further research on these factors, and provides insights which may enhance vocational services for people in treatment for moderate to severe mental illness. Finally, findings on the workplace perspective should be addressed in the practical job development efforts conducted by IPS specialists, as well as in the governmental efforts to create a more inclusive work life.Doktorgradsavhandlin

Climbing and Angles: A Study of how two Teachers Internalize and Implement the Intentions of a Teaching Experiment

In this innovative teaching experiment, the context of climbing is used to induce the teaching and learning of angle concepts. This article reports on the outcomes of a three day teaching and climbing experiment and the impact of this experience on the teacher’s understanding of meso and micro embodiments of mathematics, angle representations, as well as shifts in their attitudes about teaching/learning geometry

Compressive Sensing for Spread Spectrum Receivers

With the advent of ubiquitous computing there are two design parameters of wireless communication devices that become very important power: efficiency and production cost. Compressive sensing enables the receiver in such devices to sample below the Shannon-Nyquist sampling rate, which may lead to a decrease in the two design parameters. This paper investigates the use of Compressive Sensing (CS) in a general Code Division Multiple Access (CDMA) receiver. We show that when using spread spectrum codes in the signal domain, the CS measurement matrix may be simplified. This measurement scheme, named Compressive Spread Spectrum (CSS), allows for a simple, effective receiver design. Furthermore, we numerically evaluate the proposed receiver in terms of bit error rate under different signal to noise ratio conditions and compare it with other receiver structures. These numerical experiments show that though the bit error rate performance is degraded by the subsampling in the CS-enabled receivers, this may be remedied by including quantization in the receiver model. We also study the computational complexity of the proposed receiver design under different sparsity and measurement ratios. Our work shows that it is possible to subsample a CDMA signal using CSS and that in one example the CSS receiver outperforms the classical receiver.Comment: 11 pages, 11 figures, 1 table, accepted for publication in IEEE Transactions on Wireless Communication

Vectors in climbing

In this article, the work on mesospace embodiments of mathematics is further developed by exploring the teaching and learning of vector concepts through climbing activities. The relevance and connection between climbing and vector algebra notions is illustrated via embedded digital videos