Search

Your search keyword '"Wikberg, Emma"' showing total 30 results
Start Over Author "Wikberg, Emma"
30 results on '"Wikberg, Emma"'

2. Nontrivial ground-state degeneracies and generalized fractional excitations in the 1D lattice

Author

Wikberg, Emma

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Quantum Gases, Quantum Physics
Abstract

We study a 1D lattice Hamiltonian, relevant for a wide range of interesting physical systems like, e.g., the quantum-Hall system, cold atoms or molecules in optical lattices, and TCNQ salts. Through a tuning of the interaction parameters and a departure from a strictly convex interaction, nontrivial ground-state degeneracies and fractionally charged excitations emerge. The excitations, being a generalization of the fractional charges known from the fractional quantum-Hall effect, appear as domain walls between inequivalent ground states and carry the charge +e/mq or -e/mq, where m is an integer and associated with the specified interaction, and v = p/q is the filling fraction in the lattice. The description points at an interesting resemblance to states connected to non-Abelian statistics, which is central for the concept of topological quantum computing., Comment: 8 pages, 1 figure

Published
2012

3. Fractional domain walls from on-site softening in dipolar bosons

Author

Wikberg, Emma, Larson, Jonas, Bergholtz, Emil J., and Karlhede, Anders

Subjects
Condensed Matter - Quantum Gases, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Abstract

We study dipolar bosons in a 1D optical lattice and identify a region in parameter space---strong coupling but relatively weak on-site repulsion---hosting a series of stable charge-density-wave (CDW) states whose low-energy excitations, built from "fractional domain walls," have remarkable similarities to those of non-Abelian fractional quantum Hall states. Here, a conventional domain wall between translated CDW's may be split by inserting strings of degenerate, but inequivalent, CDW states. Outside these insulating regions, we find numerous supersolids as well as a superfluid regime. The mentioned phases should be accessible experimentally and, in particular, the fractional domain walls can be created in the ground state using single-site addressing, i.e., by locally changing the chemical potential., Comment: 6 pages, 3 figures. Extended discussion. As published

Published
2011
Full Text
View/download PDF

4. Spin chain description of rotating bosons at $\nu=1$

Author

Wikberg, Emma, Bergholtz, Emil J., and Karlhede, Anders

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Abstract

We consider bosons at Landau level filling $\nu=1$ on a thin torus. In analogy with previous work on fermions at filling $\nu =1/2$, we map the low-energy sector onto a spin-1/2 chain. While the fermionic system may realize the gapless XY-phase, we show that typically this does not happen for the bosonic system. Instead, both delta function and Coulomb interaction lead to gapped phases in the bosonic system, and in particular we identify a phase corresponding to the non-abelian Moore-Read state. In the spin language, the hamiltonian is dominated by a ferromagnetic next-nearest neighbor interaction, which leads to a description consistent with the non-trivial degeneracies of the ground and excited states of this phase of matter. In addition we comment on the similarities and differences of the two systems mentioned above and fermions at $\nu=5/2$., Comment: Published. 19 pages, 4 figures

Published
2009
Full Text
View/download PDF

5. Improvements of 177Lu SPECT images from sparsely acquired projections by reconstruction with deep-learning-generated synthetic projections.

Author

Wikberg, Emma, Essen, Martijn van, Rydén, Tobias, Svensson, Johanna, Gjertsson, Peter, and Bernhardt, Peter

Subjects
ARTIFICIAL neural networks, SINGLE-photon emission computed tomography, BONE marrow, COMPUTED tomography, STANDARD deviations, DUAL-energy X-ray absorptiometry
Abstract

Background: For dosimetry, the demand for whole-body SPECT/CT imaging, which require long acquisition durations with dual-head Anger cameras, is increasing. Here we evaluated sparsely acquired projections and assessed whether the addition of deep-learning-generated synthetic intermediate projections (SIPs) could improve the image quality while preserving dosimetric accuracy. Methods: This study included 16 patients treated with 177Lu-DOTATATE with SPECT/CT imaging (120 projections, 120P) at four time points. Deep neural networks (CUSIPs) were designed and trained to compile 90 SIPs from 30 acquired projections (30P). The 120P, 30P, and three different CUSIP sets (30P + 90 SIPs) were reconstructed using Monte Carlo-based OSEM reconstruction (yielding 120P_rec, 30P_rec, and CUSIP_recs). The noise levels were visually compared. Quantitative measures of normalised root mean square error, normalised mean absolute error, peak signal-to-noise ratio, and structural similarity were evaluated, and kidney and bone marrow absorbed doses were estimated for each reconstruction set. Results: The use of SIPs visually improved noise levels. All quantitative measures demonstrated high similarity between CUSIP sets and 120P. Linear regression showed nearly perfect concordance of the kidney and bone marrow absorbed doses for all reconstruction sets, compared to the doses of 120P_rec (R2 ≥ 0.97). Compared to 120P_rec, the mean relative difference in kidney absorbed dose, for all reconstruction sets, was within 3%. For bone marrow absorbed doses, there was a higher dissipation in relative differences, and CUSIP_recs outperformed 30P_rec in mean relative difference (within 4% compared to 9%). Kidney and bone marrow absorbed doses for 30P_rec were statistically significantly different from those of 120_rec, as opposed to the absorbed doses of the best performing CUSIP_rec, where no statistically significant difference was found. Conclusion: When performing SPECT/CT reconstruction, the use of SIPs can substantially reduce acquisition durations in SPECT/CT imaging, enabling acquisition of multiple fields of view of high image quality with satisfactory dosimetric accuracy. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

6. Degeneracy of non-abelian quantum Hall states on the torus: domain walls and conformal field theory

Author

Ardonne, Eddy, Bergholtz, Emil J., Kailasvuori, Janik, and Wikberg, Emma

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We analyze the non-abelian Read-Rezayi quantum Hall states on the torus, where it is natural to employ a mapping of the many-body problem onto a one-dimensional lattice model. On the thin torus--the Tao-Thouless (TT) limit--the interacting many-body problem is exactly solvable. The Read-Rezayi states at filling $\nu=\frac k {kM+2}$ are known to be exact ground states of a local repulsive $k+1$-body interaction, and in the TT limit this is manifested in that all states in the ground state manifold have exactly $k$ particles on any $kM+2$ consecutive sites. For $M\neq 0$ the two-body correlations of these states also imply that there is no more than one particle on $M$ adjacent sites. The fractionally charged quasiparticles and quasiholes appear as domain walls between the ground states, and we show that the number of distinct domain wall patterns gives rise to the nontrivial degeneracies, required by the non-abelian statistics of these states. In the second part of the paper we consider the quasihole degeneracies from a conformal field theory (CFT) perspective, and show that the counting of the domain wall patterns maps one to one on the CFT counting via the fusion rules. Moreover we extend the CFT analysis to topologies of higher genus., Comment: 15 pages

Published
2008
Full Text
View/download PDF

10. Evaluation of reconstruction methods and image noise levels concerning visual assessment of simulated liver lesions in 111In-octreotide SPECT imaging.

Author

Wikberg, Emma, van Essen, Martijn, Rydén, Tobias, Svensson, Johanna, Gjertsson, Peter, and Bernhardt, Peter

Subjects
*COLLIMATORS, *IMAGE reconstruction, *SINGLE-photon emission computed tomography, *EVALUATION methodology, *EARLY detection of cancer, *SIGNAL-to-noise ratio, *HEPATIC veins
Abstract

Background: Early cancer detection is crucial for patients' survival. The image quality in 111In-octreotide SPECT imaging could be improved by using Monte Carlo (MC)-based reconstruction. The aim of this observational study was to determine the detection rate of simulated liver lesions for MC-based ordered subset expectation maximization (OSEM) reconstruction compared to conventional attenuation-corrected OSEM reconstruction. Methods: Thirty-seven SPECT/CT examinations with 111In-octreotide were randomly selected. The inclusion criterion was no liver lesions at the time of examination and for the following 3 years. SPECT images of spheres representing lesions were simulated using MC. The raw data of the spheres were added to the raw data of the established healthy patients in 26 of the examinations, and the remaining 11 examinations were not modified. The images were reconstructed using conventional OSEM reconstruction with attenuation correction and post filtering (fAC OSEM) and MC-based OSEM reconstruction without and with post filtering (MC OSEM and fMC OSEM, respectively). The images were visually and blindly evaluated by a nuclear medicine specialist. The criteria evaluated were liver lesion yes or no, including coordinates if yes, with confidence level 1–3. The percentage of detected lesions and accuracy (percentage of correctly classified cases), as well as tumor-to-normal tissue concentration (TNC) ratios and signal-to-noise ratios (SNRs), were evaluated. Results: The detection rates were 30.8% for fAC OSEM, 42.3% for fMC OSEM, and 50.0% for MC OSEM. The accuracies were 45.9% for fAC OSEM, 45.9% for fMC OSEM, and 54.1% for MC OSEM. The number of false positives was higher for fMC and MC OSEM. The observer's confidence level was higher in filtered images than in unfiltered images. TNC ratios were significantly higher, statistically, with MC OSEM and fMC OSEM than with AC OSEM, but SNRs were similar due to higher noise with MC OSEM. Conclusion: One in two lesions were found using MC OSEM versus one in three using conventional reconstruction. TNC ratios were significantly improved, statistically, using MC-based reconstruction, but the noise levels increased and consequently the confidence level of the observer decreased. For further improvements, image noise needs to be suppressed. [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
View/download PDF

11. I Plan de Inclusión y Cohesión Social de Monóvar 2021-2025

Author

Universidad de Alicante. Departamento de Sociología I, Universidad de Alicante. Departamento de Sociología II, Universidad de Alicante. Departamento de Humanidades Contemporáneas, Ortega Fernández, Javier, Sanchís-Ramón, María-José, Ortuño Garrigós, Ana Isabel, Håkonsdatter Wikberg, Emma, Universidad de Alicante. Departamento de Sociología I, Universidad de Alicante. Departamento de Sociología II, Universidad de Alicante. Departamento de Humanidades Contemporáneas, Ortega Fernández, Javier, Sanchís-Ramón, María-José, Ortuño Garrigós, Ana Isabel, and Håkonsdatter Wikberg, Emma

Abstract

A través de este libro se presenta el resultado sistematizado de un proceso de investigación social aplicado para la elaboración del I Plan de Inclusión y Cohesión Social de Monóvar (Alicante). Se desarrolla a través de la articulación de diferentes técnicas de investigación, aunque prevaleciendo en todo momento una metodología cualitativa. Se elabora desde un planteamiento epistemológico de implicación y aplicabilidad, por lo que el resultado más relevante son las siete líneas estratégicas en materia de inclusión y cohesión social y cultural. Se ofrece una radiografía sociológica y antropológica sobre diferentes temáticas, véase por ejemplo los procesos de vulnerabilidad social, la exclusión de determinados colectivos sociales o los recursos culturales para la cohesión social que están funcionando.

Published
2022

12. I Plan de Inclusión y Cohesión Social de Monóvar 2021-2025

Author

Ortega Fernández, Javier, Sanchís-Ramón, María-José, Ortuño Garrigós, Ana Isabel, Håkonsdatter Wikberg, Emma, Universidad de Alicante. Departamento de Sociología I, Universidad de Alicante. Departamento de Sociología II, Universidad de Alicante. Departamento de Humanidades Contemporáneas, and CRITERI - Socioeconomia Crítica i Territori

Subjects
Cohesión Social, Inclusión Social, IAP, Planificación, Antropología Social, Sociología
Abstract

A través de este libro se presenta el resultado sistematizado de un proceso de investigación social aplicado para la elaboración del I Plan de Inclusión y Cohesión Social de Monóvar (Alicante). Se desarrolla a través de la articulación de diferentes técnicas de investigación, aunque prevaleciendo en todo momento una metodología cualitativa. Se elabora desde un planteamiento epistemológico de implicación y aplicabilidad, por lo que el resultado más relevante son las siete líneas estratégicas en materia de inclusión y cohesión social y cultural. Se ofrece una radiografía sociológica y antropológica sobre diferentes temáticas, véase por ejemplo los procesos de vulnerabilidad social, la exclusión de determinados colectivos sociales o los recursos culturales para la cohesión social que están funcionando. Vicepresidencia y Conselleria de Igualdad y Políticas Inclusivas - Generalitat Valenciana / Ayuntamiento de Monóvar

Published
2022

13. Ya soy Antropóloga ¿Y ahora qué? Experiencias de profesionales ejerciendo la antroplogía fuera de la Universidad

Author

Wikberg, Emma Håkonsdatter, Wikberg, and García Castaño, Francisco Javier

Subjects
Experiencias de profesionales, Antropología aplicada, Profesionalización de la antropología, Formación en antropología
Abstract

Este proyecto tiene como objetivo aproximarnos a las experiencias de los y las profesionales que ejercen la antropología fuera de la Academia, dando visibilidad a esta realidad que es vital para la culminación de la profesionalización en España. En un primer lugar se presenta el contexto en el que se enmarca la antropología como profesión, a través de un recorrido histórico por la disciplina. A continuación exponen los resultados del trabajo de campo, llevado a cabo a partir de entrevistas en profundidad a 13 profesionales de la antropología y la observación participante en varios congresos y jornadas cuya temática era la profesionalización. Con este contenido se realiza una aproximación etnográfica, dividida en dos capítulos principales. Primero, sobre cómo la formación en antropología condiciona la práctica profesional. Y segundo, sobre las ventajas e inconvenientes de trabajar como antropólogo/a fuera de la universidad., This Project aims to approach to the experiences of professionals who practice anthropology outside the Academy, giving visibility to this reality, which is paramount for the culmination of professionalization in Spain. In the first place, the context in which anthropology as a profession is framed is presented, through a historical journey through the discipline. Down below, they present the results of the field work, carried out from in- depth interviews with 13 anthropology professionals and the participant observation that took part in several congresses and conferences on the subject of professionalization. With this content, an ethnographic approach is made, divided into two main chapters. First, on how training in anthropology conditions professional practice. And second, about the advantages and disadvantages of working as an anthropologist outside university.

Published
2021

18. Non-abelian quantum Hall states and fractional charges in one dimension

Author

Wikberg, Emma

Subjects
Physical Sciences, Fysik, Condensed Matter Physics, Den kondenserade materiens fysik
Abstract

The fractional quantum Hall effect has, since its discovery around 30 years ago, been a vivid field of research—both experimentally and theoretically. In this thesis we investigate certain non-abelian quantum Hall states by mapping the two-dimensional system onto a thin torus, where the problem becomes effectively one-dimensional and hopping is suppressed, meaning that the classical electrostatic interaction dominates. The approach assists with a simplified view of ground states and their degeneracies, as well as of the nature of the fractionally charged, minimal excitations of the corresponding quantum Hall states. Similar models are also relevant for cold atoms trapped in one-dimensional optical lattices, where interaction parameters are available for tuning, which opens up for realizing interesting lattice states in controllable environments. The diverse applicability of the one-dimensional electrostatic lattice hamiltonian motivates the exploration of the systems and models treated in this work. In the absence of hopping or tunneling, the low-energy behavior of the one-dimensional lattice system is ultimately dependent on the nature of the electrostatic interaction present. For ordinary interactions such as Coulomb, the ground state at particle filling fraction ν= p/q has a well-known q-fold center-of-mass degeneracy and the elementary excitations are domain walls of fractional charge e* = ±e/q. These appear in abelian quantum Hall systems and are known since earlier. In this work, we show how other types of interaction give rise to increased ground state degeneracies and, as a result, to the emergence of split fractional charges recognized from non- abelian quantum Hall systems. At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript.

Published
2013

22. Fractional domain walls from on-site softening in dipolar bosons

Author

Wikberg, Emma, Larson, Jonas, Bergholtz, Emil J., Karlhede, Anders, Wikberg, Emma, Larson, Jonas, Bergholtz, Emil J., and Karlhede, Anders

Abstract

We study dipolar bosons in a 1D optical lattice and identify a region in parameter space-strong coupling but relatively weak on-site repulsion-hosting a series of stable charge-density-wave (CDW) states whose low-energy excitations, built from fractional domain walls, have remarkable similarities to those of non-Abelian fractional quantum Hall states. Here, a conventional domain wall between translated CDW's may be split by inserting strings of degenerate, but inequivalent, CDW states. Outside these insulating regions, we find numerous supersolids as well as a superfluid regime. The mentioned phases should be accessible experimentally and, in particular, the fractional domain walls can be created in the ground state using single-site addressing, i.e., by locally changing the chemical potential., 4

Published
2012
Full Text
View/download PDF

24. Pfaffian quantum Hall state made simple : Multiple vacua and domain walls on a thin torus

Author

Bergholtz, E. J., Kailasvuori, J., Wikberg, Emma, Hansson, Thors Hans, Karlhede, Anders, Bergholtz, E. J., Kailasvuori, J., Wikberg, Emma, Hansson, Thors Hans, and Karlhede, Anders

Abstract

We analyze the Moore-Read Pfaffian state on a thin torus. The known sixfold degeneracy is realized by two inequivalent crystalline states with a four- and twofold degeneracy, respectively. The fundamental quasihole and quasiparticle excitations are domain walls between these vacua, and simple counting arguments give a Hilbert space of dimension 2n−1 for 2n−k holes and k particles at fixed positions and assign each a charge ±e∕4. This generalizes the known properties of the hole excitations in the Pfaffian state as deduced using conformal field theory techniques. Numerical calculations using a model Hamiltonian and a small number of particles support the presence of a stable phase with degenerate vacua and quarter-charged domain walls also away from the thin-torus limit. A spin-chain Hamiltonian encodes the degenerate vacua and the various domain walls.

Published
2006
Full Text
View/download PDF

29. Intracranial volume is normal in infants with sagittal synostosis.

Author

Fischer, Sara, Maltese, Giovanni, Tarnow, Peter, Wikberg, Emma, Bernhardt, Peter, Tovetjärn, Robert, and Kölby, Lars

Subjects
CRANIOSYNOSTOSES, DIAGNOSTIC imaging centers, CRANIOFACIAL abnormalities, INFANTS, THERAPEUTICS
Abstract

Premature sagittal synostosis results in an elongated, narrow skull shape, scaphocephaly. It has been unclear whether the intracranial volume (ICV) of these children is different from that of normal children. The aim of the present study was to precisely determine the ICV in a large cohort of children with premature sagittal synostosis and to compare it to the ICV of a sex- and age-matched control group. All patients (n = 143) with isolated sagittal synostosis registered in the Goteborg Craniofacial Registry until the end of 2012 with a preoperative CT examination were identified. For each case, a sex- and age- (±30 days) matched control was identified from children who had undergone CT for post-traumatic or neurological reasons. The ICV was measured in a semi-automatic MATLAB program with functions such as region growing, watershed, and thresholding in axial CT slices. The ICV was calculated using the Cavalieri principle. The mean (± SEM) values of ICV for children with sagittal synostosis and for corresponding controls were 866 ± 13 ml and 870 ± 15 ml, respectively. The mean ages of these groups were 173 ± 8 days and 172 ± 8 days, respectively. Subgroup analysis of sex and age at CT (⩽180 days and >180 days) did not reveal any differences in ICV between cases and controls. Precise determination of ICV in addition to the use of adequate controls has made it possible to conclude that children with premature isolated sagittal synostosis have a normal ICV. [ABSTRACT FROM AUTHOR]

Published
2015
Full Text
View/download PDF

30. Springs produce favorable morphological outcomes compared to H-Craniectomy in a two-center comparison of matched cases

Author

Unander-Scharin, Jesper, Daniel, Nowinski, Enblad, Per, Lif, Hanna, Nysjö, Johan, Bhatti Søfteland, Madiha, Tarnow, Peter, Maltese, Giovanni, Fischer, Sara, Kölby, Lars, Wikberg, Emma, Unander-Scharin, Jesper, Daniel, Nowinski, Enblad, Per, Lif, Hanna, Nysjö, Johan, Bhatti Søfteland, Madiha, Tarnow, Peter, Maltese, Giovanni, Fischer, Sara, Kölby, Lars, and Wikberg, Emma

Abstract

Sagittal synostosis is the most common type of premature suture closure and many surgical techniques are used for correction of the scaphocephalic skull shape. Direct comparisons of the outcome of different surgical techniques for correction of craniosynostosis are rare. The aim of the present study was to compare the outcome of craniotomy combined with springs and H-craniectomy for non-syndromic sagittal synostosis. This study was enabled by the synchronization of pre- and postoperative imaging, follow-up and data collection for the two craniofacial national referral centers in Sweden, using two fundamentally different surgical techniques - Craniotomy with springs (Gothenburg) and H-Craniectomy (Uppsala). Twenty-three pairs of patients matched for sex and preoperative cephalic index (CI) were included. CI, total intracranial volume and partial intracranial volumes were measured before surgery and at 3 years of age. Perioperative data including operation time, blood loss, volume of transfused blood and length of hospital stay were also gathered. Craniotomy with springs had less bleeding and lower transfusion rates than H-craniectomy. However, the spring-assisted surgery requires two operations. Three spring-related complications occurred . The total surgery time was similar for both groups. Most importantly, in the compiled analysis of changes in CI and partial volume distribution, the craniotomy combined with springs was demonstrated to produce a superior morphological correction.

Catalog

Books, media, physical & digital resources
See catalog results