Controlled Coulomb effects in core-shell quantum rings

We analyse theoretically the possibilities of contactless control of in-gap states formed by a pair of electrons confined in a triangular quantum ring. The in-gap states are corner-localized states associated with two electrons occupying the same corner area, and thus shifted to much higher energies than other corner states, but still they are below the energies of corner-side-localized states. We show how the energies, degeneracy and splittings between consecutive levels change with the orientation of an external electric field relatively to the polygonal cross section. We also show how absorption changes in the presence of external electric and magnetic fields.Comment: 4 pages, 2 figure

Magnetotransport in a time-modulated double quantum point contact system

We report on a time-dependent Lippmann-Schwinger scattering theory that allows us to study the transport spectroscopy in a time-modulated double quantum point contact system in the presence of a perpendicular magnetic field. Magnetotransport properties involving inter-subband and inter-sideband transitions are tunable by adjusting the time-modulated split-gates and the applied magnetic field. The observed magnetic field induced Fano resonance feature may be useful for the application of quantum switching.Comment: 3 pages, 4 figure

Generalized Master equation approach to mesoscopic time-dependent transport

We use a generalized Master equation (GME) formalism to describe the non-equilibrium time-dependent transport through a short quantum wire connected to semi-infinite biased leads. The contact strength between the leads and the wire are modulated by out-of-phase time-dependent functions which simulate a turnstile device. One lead is fixed at one end of the sample whereas the other lead has a variable placement. The system is described by a lattice model. We find that the currents in both leads depend on the placement of the second lead. In the rather small bias regime we obtain transient currents flowing against the bias for short time intervals. The GME is solved numerically in small time steps without resorting to the traditional Markov and rotating wave approximations. The Coulomb interaction between the electrons in the sample is included via the exact diagonalization method

The prognostic value of injury severity, location of event, and age at injury in pediatric traumatic head injuries

Jonas G Halldorsson1, Kjell M Flekkoy2, Gudmundur B Arnkelsson3, Kristinn Tomasson4, Kristinn R Gudmundsson5, Eirikur Orn Arnarson1,61Psychological Health Services, Landspitali University Hospital, Reykjavik, Iceland; 2Department of Psychology, University of Oslo, and Department of Geriatric Medicine, Ulleval University Hospital, Oslo, Norway; 3Department of Psychology, University of Iceland, Reykjavik, Iceland; 4Administration of Occupational Safety and Health, Reykjavik, Iceland; 5Department of Neurosurgery, Landspitali University Hospital, Reykjavik, Iceland; 6Faculty of Medicine, University of Iceland, Reykjavik, IcelandAims: To estimate the prognostic value of injury severity, location of event, and demographic parameters, for symptoms of pediatric traumatic head injury (THI) 4 years later.Methods: Data were collected prospectively from Reykjavik City Hospital on all patients age 0–19 years, diagnosed with THI (n = 408) during one year. Information was collected on patient demographics, location of traumatic event, cause of injury, injury severity, and ICD-9 diagnosis. Injury severity was estimated according to the Head Injury Severity Scale (HISS). Four years post-injury, a questionnaire on late symptoms attributed to the THI was sent.Results: Symptoms reported were more common among patients with moderate/severe THI than among others (p < 0.001). The event location had prognostic value (p < 0.05). Overall, 72% of patients with moderate/severe motor vehicle-related THI reported symptoms. There was a curvilinear age effect (p < 0.05). Symptoms were least frequent in the youngest age group, 0–4 years, and most frequent in the age group 5–14 years. Gender and urban/rural residence were not significantly related to symptoms.Conclusions: Motor vehicle related moderate/severe THI resulted in a high rate of late symptoms. Location had a prognostic value. Patients with motor vehicle-related THI need special consideration regardless of injury severity.Keywords: follow-up, pediatric, symptoms, traumatic head injur

The acetylcholine index: an electroencephalographic marker of cholinergic activity in the living human brain applied to Alzheimer's disease and other dementias.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Files. This article is open access.The cholinergic hypothesis is well established and has led to the development of pharmacological treatments for Alzheimer's disease (AD). However, there has previously been no physiological means of monitoring cholinergic activity in vivo.An electroencephalography (EEG)-based acetylcholine (Ach) index reflecting the cholinergic activity in the brain was developed using data from a scopolamine challenge study. The applicability of the Ach index was examined in an elderly population of healthy controls and patients suffering from various causes of cognitive decline.The Ach index showed a strong reduction in the severe stages of AD dementia. A high correlation was demonstrated between the Ach index and cognitive function. The index was reduced in patients with mild cognitive impairment and prodromal AD, indicating a decreased cholinergic activity. When considering the distribution of the Ach index in a population of healthy elderly subjects, an age-related threshold was revealed, beyond which there is a general decline in cholinergic activity.The EEG-based Ach index provides, for the first time, a physiological means of monitoring the cholinergic activity in the human brain in vivo. This has great potential for aiding diagnosis and patient stratification as well as for monitoring disease progression and treatment response.Icelandic Technology Development Fund/051221006 Icelandic Technology Development Fund/08120600

Urban–rural differences in pediatric traumatic head injuries: A prospective nationwide study

Jonas G Halldorsson1, Kjell M Flekkoy2, Kristinn R Gudmundsson3, Gudmundur B Arnkelsson4, Eirikur Orn Arnarson1,51Psychological Health Services, Landspitali University Hospital, Reykjavik, Iceland; 2Department of Psychology, University of Oslo, Oslo, Norway; 3Department of Neurosurgery, Landspitali University Hospital, Reykjavik, Iceland; 4Faculty of Social Science, University of Iceland, Reykjavik, Iceland; 5Faculty of Medicine, University of Iceland, Reykjavik, IcelandAims: To estimate differences in the incidence of recorded traumatic head injuries by gender, age, severity, and geographical area.Methods: The study was prospective and nationwide. Data were collected from all hospitals, emergency units and healthcare centers in Iceland regarding all Icelandic children and adolescents 0–19 years old consecutively diagnosed with traumatic head injuries (N = 550) during a one-year period.Results: Annual incidence of minimal, mild, moderate/severe, and fatal head injuries (ICD-9 850–854) was 6.41 per 1000, with 95% confi dence interval (CI) 5.9, 7.0. Annual incidence of minimal head injuries (ICD-9 850) treated at emergency units was 4.65 (CI 4.2, 5.1) per 1000, mild head injuries admitted to hospital (ICD-9 850) was 1.50 (CI 1.3, 1.8) per 1000, and moderate/severe nonfatal injuries (ICD-9 851–854) was 0.21 (CI 0.1, 0.3) per 1000. Death rate was 0.05 (CI 0.0, 0.1) per 1000. Young children were at greater risk of sustaining minimal head injuries than older ones. Boys were at greater risk than girls were. In rural areas, incidence of recorded minimal head injuries was low.Conclusions: Use of nationwide estimate of the incidence of pediatric head injury shows important differences between urban and rural areas as well as between different age groups.Keywords: incidence, nationwide, pediatric, prospective, traumatic head injuries, urban-rural difference

Excitons in core-shell nanowires with polygonal cross sections

The distinctive prismatic geometry of semiconductor core-shell nanowires leads to complex localization patterns of carriers. Here, we describe the formation of optically active in-gap excitonic states induced by the interplay between localization of carriers in the corners and their mutual Coulomb interaction. To compute the energy spectra and configurations of excitons created in the conductive shell, we use a multi-electron numerical approach based on the exact solution of the multi-particle Hamiltonian for electrons in the valence and conduction bands, which includes the Coulomb interaction in a nonperturbative manner. We expose the formation of well separated quasidegenerate levels, and focus on the implications of the electron localization in the corners or on the sides of triangular, square and hexagonal cross sections. We obtain excitonic in-gap states associated with symmetrically distributed electrons in the spin singlet configuration. They acquire large contributions due to Coulomb interaction, and thus are shifted to much higher energies than other states corresponding to the conduction electron and the vacancy localized in the same corner. We compare the results of the multi-electron method with those of an electron-hole model and we show that the latter does not reproduce the singlet excitonic states. We also obtain the exciton lifetime and explain selection rules which govern the recombination process.This work was supported by the Icelandic Research Fun