Publications by authors named "Helgi Sigurdsson"

Exploring the non-Hermitian properties of semiconductor materials for optical applications is at the forefront of photonic research. However, the selection of appropriate systems to implement such photonic devices remains a topic of debate. In this work, we demonstrate that a perovskite crystal, characterized by its easy and low-cost manufacturing, when placed between two distributed Bragg reflectors with an air gap, can form a natural double microcavity.

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Background: Impact of Merkel cell polyomavirus (MCPyV) associated Merkel cell carcinoma (MCC) has not been assessed in the Icelandic population, nor in a whole population elsewhere.

Objectives: The primary objective was to assess trends in the incidence of MCC in Iceland and the association with MCPyV. Secondary objectives aimed to analyze MCC outcomes.

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Background: Melanoma is increasing worldwide, with incidence rates of invasive melanoma and melanoma in situ (MIS) varying by country.

Objective: To provide updated invasive melanoma and MIS incidence and mortality trends in Iceland and explore differences among sex and rurality.

Methods: In this whole-population study using the Icelandic Cancer Registry, patients diagnosed with invasive melanoma or MIS between 1957 and 2021 were included.

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Bound states in the continuum have recently been utilized in photonic crystal gratings to achieve strong coupling and ultralow threshold condensation of exciton-polariton quasiparticles with atypical Dirac-like features in their dispersion relation. Here, we develop the single- and many-body theory of these new effective relativistic polaritonic modes and describe their mean-field condensation dynamics facilitated by the interplay between protection from the radiative continuum and negative-mass optical trapping. Our theory accounts for tunable grating parameters giving full control over the diffractive coupling properties between guided polaritons and the radiative continuum, unexplored for polariton condensates.

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Vortices are topologically distinctive objects appearing as phase twists in coherent fields of optical beams and Bose-Einstein condensates. Structured networks and artificial lattices of coupled vortices could offer a powerful platform to study and simulate interaction mechanisms between constituents of condensed matter systems, such as antiferromagnetic interactions, by replacement of spin angular momentum with orbital angular momentum. Here, we realize such a platform using a macroscopic quantum fluid of light based on exciton-polariton condensates.

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Perovskite crystals-with their exceptional nonlinear optical properties, lasing and waveguiding capabilities-offer a promising platform for integrated photonic circuitry within the strong-coupling regime at room temperature. Here we demonstrate a versatile template-assisted method to efficiently fabricate large-scale waveguiding perovskite crystals of arbitrarily predefined geometry such as microwires, couplers and splitters. We non-resonantly stimulate a condensate of waveguided exciton-polaritons resulting in bright polariton lasing from the transverse interfaces and corners of our perovskite microstructures.

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Intrauterine devices (IUDs) are a safe and common form of contraception. Uterine rupture and migration of the IUD is a rare complication of insertion but can be serious and cause damage to adjacent organs. We present a case report of a 43 year old woman with chronic abdominal pain who was diagnosed with an IUD in the wall of the sigmoid colon.

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The appearance of quantized vortices in the classical "rotating bucket" experiments of liquid helium and ultracold dilute gases provides the means for fundamental and comparative studies of different superfluids. Here, we realize the rotating bucket experiment for optically trapped quantum fluid of light based on exciton-polariton Bose-Einstein condensate in semiconductor microcavity. We use the beating note of two frequency-stabilized single-mode lasers to generate an asymmetric time-periodic rotating, nonresonant excitation profile that both injects and stirs the condensate through its interaction with a background exciton reservoir.

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The field of spinoptronics is underpinned by good control over photonic spin-orbit coupling in devices that have strong optical nonlinearities. Such devices might hold the key to a new era of optoelectronics where momentum and polarization degrees of freedom of light are interwoven and interfaced with electronics. However, manipulating photons through electrical means is a daunting task given their charge neutrality.

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We demonstrate spontaneous formation of a nonlinear vortex cluster state in a microcavity exciton-polariton condensate with time-periodic sign flipping of its topological charges at the GHz scale. When optically pumped with a ring-shaped nonresonant laser, the trapped condensate experiences intricate high-order mode competition and fractures into two distinct trap levels. The resulting mode interference leads to robust condensate density beatings with periodic appearance of orderly arranged phase singularities.

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Spin-orbit interactions which couple the spin of a particle with its momentum degrees of freedom lie at the center of spintronic applications. Of special interest in semiconductor physics are Rashba and Dresselhaus spin-orbit coupling. When equal in strength, the Rashba and Dresselhaus fields result in SU(2) spin rotation symmetry and emergence of the persistent spin helix only investigated for charge carriers in semiconductor quantum wells.

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Vorticity is a key ingredient to a broad variety of fluid phenomena, and its quantised version is considered to be the hallmark of superfluidity. Circulating flows that correspond to vortices of a large topological charge, termed giant vortices, are notoriously difficult to realise and even when externally imprinted, they are unstable, breaking into many vortices of a single charge. In spite of many theoretical proposals on the formation and stabilisation of giant vortices in ultra-cold atomic Bose-Einstein condensates and other superfluid systems, their experimental realisation remains elusive.

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Introduction: Self-expandable metal stents (SEMS) are a known treatment option for obstruction due to colorectal cancer. The objective of this project was to estimate the usage of such stents in Iceland between 2000-2018. We evaluated the number of patients who received the stent as a bridge to surgery (BtoS) or as a palliative therapy (PT) and evaluated complication rate and the technical and clinical success rate.

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Using a sub-millimeter exciton-polariton waveguide suitable for integrated photonics, we experimentally demonstrate nonlinear modulation of pico-Joule pulses at the same time as amplification sufficient to compensate the system losses. By comparison with a numerical model we explain the observed interplay of gain and nonlinearity as amplification of the interacting polariton field by stimulated scattering from an incoherent continuous-wave reservoir that is depleted by the pulses. This combination of gain and giant ultrafast nonlinearity operating on picosecond pulses has the potential to open up new directions in low-power all-optical information processing and nonlinear photonic simulation of conservative and driven-dissipative systems.

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Purpose - We wanted to examine the potential of the Scandinavian Sarcoma Group (SSG) Central Register, and evaluate referral and treatment practice for soft-tissue sarcomas in the extremities and trunk wall (STS) in the Nordic countries. Background - Based on incidence rates from the literature, 8,150 (7,000-9,300) cases of STS of the extremity and trunk wall should have been diagnosed in Norway, Finland, Iceland, and Sweden from 1987 through 2011. The SSG Register has 6,027 cases registered from this period, with 5,837 having complete registration of key variables.

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Background: The impact of an inherited BRCA2 mutation on the prognosis of women with breast cancer has not been well documented. We studied the effects of oestrogen receptor (ER) status, other prognostic factors and treatments on survival in a large cohort of BRCA2 mutation carriers.

Methods: We identified 285 breast cancer patients with a 999del5 BRCA2 mutation and matched them with 570 non-carrier patients.

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Article Synopsis
  • BRCA2 mutation carriers have a significantly higher risk of death from breast cancer compared to noncarriers, particularly in those with diploid tumours.
  • The study analyzed the long-term survival of 2,967 Icelandic breast cancer patients, revealing that adverse prognostic factors differ between mutation carriers and noncarriers.
  • Findings suggest that while BRCA2 carriers face worse outcomes overall, those with aneuploid tumours experience similar survival rates to noncarriers.
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Wound control in laparostomy for the treatment of intra-abdominal hypertension remains challenging and numerous techniques have been described. We report the first UK experience with a new commercially available device specifically designed to facilitate management of the open abdomen. A 44-year-old gentleman presented with a 3-day history of constant severe epigastric pain and associated vomiting.

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To identify new risk variants for cutaneous basal cell carcinoma, we performed a genome-wide association study of 16 million SNPs identified through whole-genome sequencing of 457 Icelanders. We imputed genotypes for 41,675 Illumina SNP chip-typed Icelanders and their relatives. In the discovery phase, the strongest signal came from rs78378222[C] (odds ratio (OR) = 2.

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Objective: To study the epidemiology and severity of C. difficile infections (CDI) at Landspítali over 11 year period, 1998-2008.

Material And Methods: CDI were identified by a positive toxin assay in stools from the database of the Department of Microbiology.

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We used an approach that we term ancestry-shift refinement mapping to investigate an association, originally discovered in a GWAS of a Chinese population, between rs2046210[T] and breast cancer susceptibility. The locus is on 6q25.1 in proximity to the C6orf97 and estrogen receptor alpha (ESR1) genes.

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Effects of susceptibility variants may depend on from which parent they are inherited. Although many associations between sequence variants and human traits have been discovered through genome-wide associations, the impact of parental origin has largely been ignored. Here we show that for 38,167 Icelanders genotyped using single nucleotide polymorphism (SNP) chips, the parental origin of most alleles can be determined.

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Introduction: About 25% of patients with rectal cancer have incurable disease at the time of diagnosis. In the current study from Western Norway (population of 981 000) we focused on the utilisation of specialist care in patients with primarily incurable rectal cancer.

Patients And Methods: Between 1997 and 2002, 1 167 patients were diagnosed with rectal cancer, of whom 297 (25%) had incurable disease, according to consecutive and prospective reporting to the Norwegian Colorectal Cancer Registry.

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Vacuum-assisted closure (VAC) is a well-established treatment for complicated wound infections and chronic wounds, including poststernotomy mediastinitis. The use of VAC in treating high-energy trauma has been more limited. We present a case where VAC was successfully used to treat a contaminated self-inflicted gunshot-wound of the chest and abdomen.

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