69 research outputs found
Charge dynamics in molecular junctions: Nonequilibrium Green's Function approach made fast
Real-time Green's function simulations of molecular junctions (open quantum
systems) are typically performed by solving the Kadanoff-Baym equations (KBE).
The KBE, however, impose a serious limitation on the maximum propagation time
due to the large memory storage needed. In this work we propose a simplified
Green's function approach based on the Generalized Kadanoff-Baym Ansatz (GKBA)
to overcome the KBE limitation on time, significantly speed up the
calculations, and yet stay close to the KBE results. This is achieved through a
twofold advance: first we show how to make the GKBA work in open systems and
then construct a suitable quasi-particle propagator that includes correlation
effects in a diagrammatic fashion. We also provide evidence that our GKBA
scheme, although already in good agreement with the KBE approach, can be
further improved without increasing the computational cost.Comment: 13 pages, 13 figure
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
Longitudinal Validity and Minimal Important Change for the Modified Lower Extremity Functional Scale (LEFS) in Orthopedic Foot and Ankle Patients
The lower extremity functional scale (LEFS) is a patient-reported outcome measure for lower extremity disorders. Aim of this study was to assess the longitudinal validity including responsiveness and test-retest reliability of the revised 15-item version, and to define the minimal important change (MIC) of the modified LEFS in a generic sample of orthopedic foot and ankle patients who underwent surgery. Responsiveness, effect size, and standardized response mean were measured by determining the score change between the baseline and 6 months administration of the LEFS from 156 patients. There was no significant difference between preoperative (median 78, interquartile range [IQR] 64.2-90.3) and postoperative (median 75.0, IQR 61.7-95.0) scores. Both effect size and standardized response mean were low (0.06 and 0.06, respectively). Test-retest reliability of the LEFS was satisfactory. Intraclass correlation coefficient was 0.85 (95% confidence interval 0.81-0.88). MIC value could not be estimated due to the lack of significant score change. The modified LEFS presented with relatively low longitudinal validity in a cohort of generic orthopedic foot and ankle patients. The findings of this study indicate that the modified LEFS might not be the optimal instrument in assessing the clinical change over time for these patients. (c) 2021 The Author(s). This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)Peer reviewe
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
Validation of the Finnish FACE-Q for use in patients undergoing surgery for functional problems or malignancy
The aim of this study was to produce a Finnish version of the FACE-Q scales Satisfaction with Forehead and Eyebrows, Adverse effects: Forehead, Eyebrows and Scalp, and Adverse effects: Cheeks, Lower face and Neck, and assess the performance of these scales and the Satisfaction with Facial Appearance, Satisfaction with Outcome and Appearance-related Psychosocial Distress in patients who had undergone surgery for functional problems or malignancy affecting the forehead or cheeks. The general health-related outcomes instrument 15 D was used as a reference. Patients who had undergone a frontal lift, a direct brow lift, a facelift or an excision of a facial tumor in Helsinki University Hospital plastic surgery department in 2009-2019 were identified. A postal survey study was conducted with 305 patients, of whom 135 (44%) responded. Diagnoses included facial nerve dysfunction (53%), brow ptosis (21%) and skin, mucosal or salivary gland tumor (20%). The FACE-Q scales displayed high internal consistency (Cronbach's alphas >= 0.80) and good reliability on repeat administration. The exploratory factor analysis revealed unifactorial influences for all scales except the Adverse effects: Forehead, Eyebrows and Scalp. Weak correlations with 15 D dimensions were detected. The FACE-Q scales evaluated here are suitable for use in patients with functional problems or malignancy.Peer reviewe
Application of the FACE-Q rhinoplasty module in a mixed reconstructive and corrective rhinoplasty population in Finland
The FACE-Q Rhinoplasty module is a patient-reported outcome instrument developed for the assessment of primarily aesthetic outcomes of rhinoplasty. The aim of our study was to produce a Finnish version of the instrument and validate it for use in patients undergoing nasal reconstruction as well as those treated with a rhinoplasty. Finnish versions of the FACE-Q scales Satisfaction with Nose, Satisfaction with Nostrils and Adverse Effects: Nose, were translated following established guidelines. Patients undergoing nasal resection, reconstruction or rhinoplasty in Helsinki University Hospital plastic surgery department in 2009-2019 were identified using theatre records. A total of 240 Finnish-speaking patients 18-85 years old were approached with a postal survey questionnaire. The questionnaire included the translated FACE-Q modules and those for Satisfaction with Facial Appearance, Appearance-Related Psychosocial Distress and Satisfaction with Outcome, as well as the general health-related quality of life instrument 15 D. The FACE-Q scales translated readily to Finnish. Eighty-three patients (35%) responded to the survey. Most FACE-Q scales performed well with high internal consistency (Cronbach's alphas 0.87-0.92) and repeatability. Only the Adverse Effects: Nose scale displayed poor consistency and a floor effect with 18% of the patients reporting no adverse outcomes. Answers to the Appearance-Related Psychosocial Distress scale were skewed towards no experienced stress. Answers to the other scales were normally distributed with weak correlation with 15 D dimensions. The Finnish translations of the FACE-Q Rhinoplasty scales perform well at assessing a diverse group of patients including those undergoing nasal reconstruction as well as those undergoing rhinoplasty.Peer reviewe
Longitudinal Validity and Minimal Important Change for the Modified Lower Extremity Functional Scale (LEFS) in Orthopedic Foot and Ankle Patients
The lower extremity functional scale (LEFS) is a patient-reported outcome measure for lower extremity disorders. Aim of this study was to assess the longitudinal validity including responsiveness and test-retest reliability of the revised 15-item version, and to define the minimal important change (MIC) of the modified LEFS in a generic sample of orthopedic foot and ankle patients who underwent surgery. Responsiveness, effect size, and standardized response mean were measured by determining the score change between the baseline and 6 months administration of the LEFS from 156 patients. There was no significant difference between preoperative (median 78, interquartile range [IQR] 64.2-90.3) and postoperative (median 75.0, IQR 61.7-95.0) scores. Both effect size and standardized response mean were low (0.06 and 0.06, respectively). Test-retest reliability of the LEFS was satisfactory. Intraclass correlation coefficient was 0.85 (95% confidence interval 0.81-0.88). MIC value could not be estimated due to the lack of significant score change. The modified LEFS presented with relatively low longitudinal validity in a cohort of generic orthopedic foot and ankle patients. The findings of this study indicate that the modified LEFS might not be the optimal instrument in assessing the clinical change over time for these patients.</p
Non-adiabatic and time-resolved photoelectron spectroscopy for molecular systems
We quantify the non-adiabatic contributions to the vibronic sidebands of
equilibrium and explicitly time-resolved non-equilibrium photoelectron spectra
for a vibronic model system of Trans-Polyacetylene. Using exact
diagonalization, we directly evaluate the sum-over-states expressions for the
linear-response photocurrent. We show that spurious peaks appear in the
Born-Oppenheimer approximation for the vibronic spectral function, which are
not present in the exact spectral function of the system. The effect can be
traced back to the factorized nature of the Born-Oppenheimer initial and final
photoemission states and also persists when either only initial, or final
states are replaced by correlated vibronic states. Only when correlated initial
and final vibronic states are taken into account, the spurious spectral weights
of the Born-Oppenheimer approximation are suppressed. In the non-equilibrium
case, we illustrate for an initial Franck-Condon excitation and an explicit
pump-pulse excitation how the vibronic wavepacket motion of the system can be
traced in the time-resolved photoelectron spectra as function of the pump-probe
delay
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 60Â 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 30Â dB HL or more by age 70Â years, and 55% of men and 45% of women by age 80Â 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
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