Real-time switching between multiple steady-states in quantum transport

We study transport through an interacting model system consisting of a central correlated site coupled to finite bandwidth tight-binding leads, which are considered as effectively noninteracting. Its nonequilibrium properties are determined by real-time propagation of the Kadanoff-Baym equations after applying a bias voltage to the system. The electronic interactions on the central site are incorporated by means of self-energy approximations at Hartree-Fock, second Born and GW level. We investigate the conditions under which multiple steady-state solutions occur within different self-energy approximations, and analyze in detail the nature of these states from an analysis of their spectral functions. At the Hartree-Fock level at least two stable steady-state solutions with different densities and currents can be found. By applying a gate voltage-pulse at a given time we are able to switch between these solutions. With the same parameters we find only one steady-state solution when the self-consistent second Born and GW approximations are considered. We therefore conclude that treatment of many-body interactions beyond mean-field can destroy bistability and lead to qualitatively different results as compared those at mean-field level.Comment: 10 pages, 8 figures, Submitted at "Progress in Nonequilibrium Green's Functions IV" conferenc

Comparative study of many-body perturbation theory and time-dependent density functional theory in the out-of-equilibrium Anderson model

We study time-dependent electron transport through an Anderson model. The electronic interactions on the impurity site are included via the self-energy approximations at Hartree-Fock (HF), second Born (2B), GW, and T-Matrix level as well as within a time-dependent density functional (TDDFT) scheme based on the adiabatic Bethe-Ansatz local density approximation (ABALDA) for the exchange correlation potential. The Anderson model is driven out of equilibrium by applying a bias to the leads and its nonequilibrium dynamics is determined by real-time propagation. The time-dependent currents and densities are compared to benchmark results obtained with the time-dependent density matrix renormalization group (tDMRG) method. Many-body perturbation theory beyond HF gives results in close agreement with tDMRG especially within the 2B approximation. We find that the TDDFT approach with the ABALDA approximation produces accurate results for the densities on the impurity site but overestimates the currents. This problem is found to have its origin in an overestimation of the lead densities which indicates that the exchange correlation potential must attain nonzero values in the leads.Comment: 11 pages, 9 figure

Correlation effects in bistability at the nanoscale: steady state and beyond

The possibility of finding multistability in the density and current of an interacting nanoscale junction coupled to semi-infinite leads is studied at various levels of approximation. The system is driven out of equilibrium by an external bias and the non-equilibrium properties are determined by real-time propagation using both time-dependent density functional theory (TDDFT) and many-body perturbation theory (MBPT). In TDDFT the exchange-correlation effects are described within a recently proposed adiabatic local density approximation (ALDA). In MBPT the electron-electron interaction is incorporated in a many-body self-energy which is then approximated at the Hartree-Fock (HF), second-Born (2B) and GW level. Assuming the existence of a steady-state and solving directly the steady-state equations we find multiple solutions in the HF approximation and within the ALDA. In these cases we investigate if and how these solutions can be reached through time evolution and how to reversibly switch between them. We further show that for the same cases the inclusion of dynamical correlation effects suppresses bistability.Comment: 13 pages, 12 figure

Prevalence of age-related hearing loss in Europe: a review

Populations are becoming progressively older thus presenting symptoms of diminished organ function due to degenerative processes. These may be physiological or caused by additional factors damaging the organ. Presbyacusis refers to the physiological age-related changes of the peripheral and central auditory system leading to hearing impairment and difficulty understanding spoken language. In contrast to epidemiological data of other continents, the prevalence of age-related hearing loss (ARHL) in Europe is not well defined, due in part to the use of different classification systems. We performed a systematic literature review with the aim of gaining a picture of the prevalence of ARHL in Europe. The review included only population and epidemiological studies in English since 1970 with samples in European countries with subjects aged 60 years and above. Nineteen studies met our selection criteria and additional five studies reported self-reported hearing impairment. When these data were crudely averaged and interpolated, roughly 30% of men and 20% of women in Europe were found to have a hearing loss of 30 dB HL or more by age 70 years, and 55% of men and 45% of women by age 80 years. Apparent problems in comparing the available data were the heterogeneity of measures and cut-offs for grades of hearing impairment. Our systematic review of epidemiological data revealed more information gaps than information that would allow gaining a meaningful picture of prevalence of ARHL. The need for standardized procedures when collecting and reporting epidemiological data on hearing loss has become evident. Development of hearing loss over time in conjunction with the increase in life expectancy is a major factor determining strategies of detection and correction of ARHL. Thus, we recommend using the WHO classification of hearing loss strictly and including standard audiometric measures in population-based health surveys

Power Loading-Induced Fatigue is Influenced by Menstrual Cycle Phase

Purpose To examine the effects of fatiguing power-loading on neuromuscular properties, force production, and metabolic capacities during four phases of the menstrual cycle (MC); menstruation (M), mid-follicular (mid FOL), ovulation (OV), and mid-luteal (mid LUT). Methods Sixteen eumenorrheic women performed sessions of maximal explosive leg press (2x10 at 60%1RM load with 2 min recovery between sets). Serum hormones and neuromuscular responses were measured. Results The loading protocol significantly decreased power (between -14.2% and -12.5%; p < 0.001) and maximal force production (between MVC; -15.0% and -7.8%; p < 0.001–0.05), while decreasing activation level (between AL; -6.9% and -2.2%; p < 0.001–0.05) in all MC-phases. The decreases in AL were greater during mid LUT (p < 0.01) compared to OV. Changes in MVC and AL associated (r2 = 0.53; p < 0.01) at all MC-phases. The decrease in EMG during MVC did not differ between the MC-phases, however, mean power frequency was higher during M (+7.7%; p < 0.05) and mid LUT (+3.1%; p < 0.05) compared to OV (-7.5%). Resting twitch force decreased during mid FOL (-6.9%; p < 0.05) and mid LUT (-16.2%; p < 0.001), and these values were significantly decreased (p < 0.05) compared to OV. In addition, resting twitch force at mid LUT was lower (p < 0.01) compared to M. Blood lactate levels increased more (p < 0.05) during M compared to mid LUT. Some serum hormone concentrations associated with fatigue-induced changes in neuromuscular properties and force production, but these correlations behaved differently between the MC-phases. Conclusions OV may offer a more favorable hormonal milieu for acute neural responses, while mid FOL and mid LUT appear to be superior for acute muscular responses.peerReviewe

Epidemiology of A3243G, the mutation for mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes: prevalence of the mutation in an adult population.

Mitochondrial diseases are characterized by considerable clinical variability and are most often caused by mutations in mtDNA. Because of the phenotypic variability, epidemiological studies of the frequency of these disorders have been difficult to perform. We studied the prevalence of the mtDNA mutation at nucleotide 3243 in an adult population of 245,201 individuals. This mutation is the most common molecular etiology of MELAS syndrome (mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes), one of the clinical entities among the mitochondrial disorders. Patients with diabetes mellitus, sensorineural hearing impairment, epilepsy, occipital brain infarct, ophthalmoplegia, cerebral white-matter disease, basal-ganglia calcifications, hypertrophic cardiomyopathy, or ataxia were ascertained on the basis of defined clinical criteria and family-history data. A total of 615 patients were identified, and 480 samples were examined for the mutation. The mutation was found in 11 pedigrees, and its frequency was calculated to be >=16. 3/100,000 in the adult population (95% confidence interval 11.3-21. 4/100,000). The mutation had arisen in the population at least nine times, as determined by mtDNA haplotyping. Clinical evaluation of the probands revealed a syndrome that most frequently consisted of hearing impairment, cognitive decline, and short stature. The high prevalence of the common MELAS mutation in the adult population suggests that mitochondrial disorders constitute one of the largest diagnostic categories of neurogenetic diseases

Tympanostomies and tonsillar surgery in children during the COVID-19 pandemic in Finland

Abstract Objective: To assess the impact of social restrictions due to COVID‐19 on the number of tympanostomies and tonsillar surgeries in children. Methods: Incidences were calculated per 100 000 children for tonsillar surgery and tympanostomies in 2020 and compared to the mean incidence of referral years 2017 to 2019 by incidence rate ratios (IRR) with 95% confidence intervals (CIs). Median waiting times were also compared. Results: Before the lockdown, tonsillar surgery incidence was 33.4/100000 (IRR 1.14, CI 0.76–1.71) in February 2020. After the lockdown began, the incidence of tonsillar surgery was 1.4/100000 (IRR 0.04, CI 0.01–0.15) in April. In June, tonsillar operation incidence started to increase (20.4 per 100 000). The incidence of tympanostomies was 81% lower (IRR 0.19, CI 0.09–0.39) in April 2020 and 61% lower (IRR 0.39, CI 0.22–0.69) in August 2020 than in 2017‐2019. These incidence rates remained lower all year (December 2020 IRR 0.13, CI 0.05–0.33). Median waiting time for tonsillar surgery was 3.3 months in 2020 and 1.6 months in 2017 to 2019; P &lt;.001, and for tympanostomies 1.3 months in 2020 and 1.0 months in 2017 to 2019, P &lt;.001. The referral rate to otorhinolaryngology during the severest restrictions was 35% lower in April and May 2020 compared with the reference years. Conclusion: This study suggests that the restrictions against COVID‐19 reduced the incidence rates of tonsil surgery and tympanostomies in children. Also, the lockdown and cancellations of elective operations in spring 2020 led to increased waiting times. These findings may help in preparing for future pandemics