Electric field measurements with stratospheric balloons

Electric fields and currents in the middle atmosphere are important elements of the modern picture of this region. Balloon instruments, reaching the level of the stratosphere, were used extensively for the experimental work. The research has shown good progress, both in the MAP period and in the years before and after. The knowledge was increased about, e.g., the upper atmosphere potential, the electric properties of the medium itself and about the coupling with magnetospheric (ionospheric) fields and currents. Also various measurements have brought about a discussion of the possible existence of hitherto unknown sources. Throughout the MAP period the work on a possible definition of an electric index has continued

Evidence for a direct band gap in the topological insulator Bi2Se3 from theory and experiment

Using angle-resolved photoelectron spectroscopy and ab-initio GW calculations, we unambiguously show that the widely investigated three-dimensional topological insulator Bi2Se3 has a direct band gap at the Gamma point. Experimentally, this is shown by a three-dimensional band mapping in large fractions of the Brillouin zone. Theoretically, we demonstrate that the valence band maximum is located at the Brillouin center only if many-body effects are included in the calculation. Otherwise, it is found in a high-symmetry mirror plane away from the zone center.Comment: 8 pages, 4 figure

Kan vi stole på lærebøkene? En kvalitativ studie om samsvaret mellom læreplanmål og lærebøker

I denne masteravhandlingen belyses samsvaret mellom kompetansemålene i LK06 og et utvalg av lærebøker som benyttes i undervisningen på mellomtrinnet i den norske grunnskolen. Studien baserer seg på en kvalitativ tilnærming der jeg benytter meg av kvalitativ tekstanalyse som forskningsmetode. I studien blir det først foretatt en analyse av kompetansemålene i LK06. Dette blir gjort ved å dele de komplekst sammensatte kompetansemålene i mindre delmål bestående av ferdigheter og kunnskaper. Ved å benytte meg av begrepene sterk og svak innramming har jeg videre vurdert graden av valgfrihet som ligger i hvert enkelt av disse delmålene. Det vil si i hvor stor grad elevene selv kan være med på å bestemme hvordan kompetansen i de ulike delmålene skal oppnås. Ut fra denne inndelingen har jeg utarbeidet et analyseskjema som har gjort det mulig å identifisere den tilsvarende kompetansen i lærebøkene. Ut fra mine tolkninger kategoriserte jeg graden av samsvar mellom kompetansemålenes delmål og lærebøkenes innhold i tre kategorier; godt samsvar, delvis samsvar og manglende samsvar. Til slutt ble resultatet innenfor hver av disse kategoriene tallfestet for å skape oversikt over analyseresultatene. Sentrale funn i studien viser at innholdet i de undersøkte lærebøkene i stor grad samsvarer med kompetansemålene i LK06. Funnene i studien er sett i lys av grundig drøfting av studiens validitet og reliabilitet

In-plane magnetic anisotropy of Fe atoms on Bi2_2Se3_3(111)

The robustness of the gapless topological surface state hosted by a 3D topological insulator against perturbations of magnetic origin has been the focus of recent investigations. We present a comprehensive study of the magnetic properties of Fe impurities on a prototypical 3D topological insulator Bi$_2$Se$_3$ using local low temperature scanning tunneling microscopy and integral x-ray magnetic circular dichroism techniques. Single Fe adatoms on the Bi$_2$Se$_3$ surface, in the coverage range $\approx 1$ are heavily relaxed into the surface and exhibit a magnetic easy axis within the surface-plane, contrary to what was assumed in recent investigations on the opening of a gap. Using \textit{ab initio} approaches, we demonstrate that an in-plane easy axis arises from the combination of the crystal field and dynamic hybridization effects.Comment: 5 pages, 3 figures, typos correcte

Multi-method observations and modelling of the three-dimensional currents associated with a very strong Ps6 event

A pulsation event has been studied which showed Ps6-type characteristics with a period of about 20 min. Data from a number of magnetometer and riometer measurements over a large area have been combined with balloon measurements of the electric field to obtain a detailed description of the ionospheric current system during the event. The pulsations reported here occured over an interval longer than 3 h and showed large magnetic variations, up to 700 nT.  A model of the three-dimensional current flow has been derived which agrees with the data. It is concluded that most of the magnetic disturbance measured on the ground is caused by Hall-currents.           ARK: https://n2t.net/ark:/88439/y016745 Permalink: https://geophysicsjournal.com/article/211 &nbsp

On the minimization of Dirichlet eigenvalues of the Laplace operator

We study the variational problem \inf \{\lambda_k(\Omega): \Omega\ \textup{open in}\ \R^m,\ |\Omega| < \infty, \ \h(\partial \Omega) \le 1 \}, where $\lambda_k(\Omega)$ is the $k$'th eigenvalue of the Dirichlet Laplacian acting in $L^2(\Omega)$, \h(\partial \Omega) is the $(m-1)$- dimensional Hausdorff measure of the boundary of $\Omega$, and $|\Omega|$ is the Lebesgue measure of $\Omega$. If $m=2$, and $k=2,3, \cdots$, then there exists a convex minimiser $\Omega_{2,k}$. If $m \ge 2$, and if $\Omega_{m,k}$ is a minimiser, then $\Omega_{m,k}^*:= \textup{int}(\overline{\Omega_{m,k}})$ is also a minimiser, and $\R^m\setminus \Omega_{m,k}^*$ is connected. Upper bounds are obtained for the number of components of $\Omega_{m,k}$. It is shown that if $m\ge 3$, and $k\le m+1$ then $\Omega_{m,k}$ has at most $4$ components. Furthermore $\Omega_{m,k}$ is connected in the following cases : (i) $m\ge 2, k=2,$ (ii) $m=3,4,5,$ and $k=3,4,$ (iii) $m=4,5,$ and $k=5,$ (iv) $m=5$ and $k=6$. Finally, upper bounds on the number of components are obtained for minimisers for other constraints such as the Lebesgue measure and the torsional rigidity.Comment: 16 page

Embeddings of SL(2,Z) into the Cremona group

Geometric and dynamic properties of embeddings of SL(2,Z) into the Cremona group are studied. Infinitely many non-conjugate embeddings which preserve the type (i.e. which send elliptic, parabolic and hyperbolic elements onto elements of the same type) are provided. The existence of infinitely many non-conjugate elliptic, parabolic and hyperbolic embeddings is also shown. In particular, a group G of automorphisms of a smooth surface S obtained by blowing-up 10 points of the complex projective plane is given. The group G is isomorphic to SL(2,Z), preserves an elliptic curve and all its elements of infinite order are hyperbolic.Comment: to appear in Transformation Group

Health-related quality of life from 20 to 32 years of age in very low birth weight individuals : a longitudinal study

Background Preterm birth with very low birth weight (VLBW, birth weight < 1500 g) is associated with health problems later in life. How VLBW individuals perceive their physical and mental health-related quality of life (HRQoL) is important to understand their putative burden of disease. Previous studies have shown mixed results, and longitudinal studies into adulthood have been requested. This study aimed to investigate differences in HRQoL between preterm VLBW and term born individuals at 32 years of age, and to study changes in HRQoL from 20 to 32 years. Methods In a geographically based longitudinal study, 45 VLBW and 68 term born control participants completed the Short Form 36 Health Survey (SF-36) at 32 years of age. Data from three previous timepoints was also available (20, 23 and 28 years of age). The SF-36 yields eight domain scores as well as a physical and a mental component summary. Between-group differences in these variables were investigated. We also performed subgroup analyses excluding individuals with disabilities, i.e., cerebral palsy and/or low estimated intelligence quotient. Results At 32 years of age, the physical component summary was 5.1 points lower (95% confidence interval (CI): 8.6 to 1.6), and the mental component summary 4.1 points lower (95% CI: 8.4 to - 0.3) in the VLBW group compared with the control group. For both physical and mental component summaries there was an overall decline in HRQoL from 20 to 32 years of age in the VLBW group. When we excluded individuals with disabilities (n = 10), group differences in domain scores at 32 years were reduced, but physical functioning, bodily pain, general health, and role-emotional scores remained lower in the VLBW subgroup without disabilities compared with the control group. Conclusion We found that VLBW individuals reported lower HRQoL than term born controls at 32 years of age, and that HRQoL declined in the VLBW group from 20 to 32 years of age. This was in part, but not exclusively explained by VLBW individuals with disabilities.Peer reviewe