Persistent Currents in Small, Imperfect Hubbard Rings

We have done a study with small, imperfect Hubbard rings with exact diagonalization. The results for few-electron rings show, that the imperfection, whether localized or not, nearly always decrease, but can also \emph{increase} the persistent current, depending on the character of the imperfection and the on-site interaction. The calculations are generally in agreement with more specialized studies. In most cases the electron spin plays an important role.Comment: 6 pages, 4 figure

Association of shift work with mood disorders and sleep problems according to chronotype: a 17-year cohort study

Both evening chronotype and shift work are associated with depressive symptoms. This study examined whether the association between shift work and mood disorders and sleep problems varies by chronotype. The study population included 10637 participants from the Finnish Hospital Personnel Cohort Study. Work schedule was assessed using repeated questionnaires between 2000 and 2017. Chronotype, assessed using a single item from the Diurnal Type Scale, was categorized into definite morning, somewhat morning, somewhat evening, and definite evening types. The presence of mood disorders was identified by the 12-item General Health Questionnaire. Sleep problems were assessed by self-reported frequency of difficulty falling asleep and maintaining asleep. Longitudinal fixed effects models were used to examine the associations between shift work and the presence of mood disorders and sleep problems, stratified by chronotype. We found that fixed night work was associated with mood disorders among somewhat evening (adjusted odds ratio [OR] 1.91, 95% CI 1.09-3.34) and definite evening-type workers (adjusted OR 2.05, 95% CI 1.06-3.98). Shift work with night shifts was associated with mood disorders among definite evening-type workers (adjusted OR 1.75, 95% CI 1.18-2.60). Similarly, fixed night work was associated with difficulty maintaining sleep only among evening-type workers. In conclusion, evening chronotype increase the vulnerability to mood disorders and sleep disturbances related to night work

On the formation of Wigner molecules in small quantum dots

It was recently argued that in small quantum dots the electrons could crystallize at much higher densities than in the infinite two-dimensional electron gas. We compare predictions that the onset of spin polarization and the formation of Wigner molecules occurs at a density parameter $r_s\approx 4 a_B^*$ to the results of a straight-forward diagonalization of the Hamiltonian matrix

Spectral properties of rotating electrons in quantum dots and their relation to quantum Hall liquids

The exact diagonalization technique is used to study many-particle properties of interacting electrons with spin, confined in a two-dimensional harmonic potential. The single-particle basis is limited to the lowest Landau level. The results are analyzed as a function of the total angular momentum of the system. Only at angular momenta corresponding to the filling factors 1, 1/3, 1/5 etc. the system is fully polarized. The lowest energy states exhibit spin-waves, domains, and localization, depending on the angular momentum. Vortices exist only at excited polarized states. The high angular momentum limit shows localization of electrons and separation of the charge and spin excitations.Comment: 14 pages 18 figure

Rotational and vibrational spectra of quantum rings

One can confine the two-dimensional electron gas in semiconductor heterostructures electrostatically or by etching techniques such that a small electron island is formed. These man-made ``artificial atoms'' provide the experimental realization of a text-book example of many-particle physics: a finite number of quantum particles in a trap. Much effort was spent on making such "quantum dots" smaller and going from the mesoscopic to the quantum regime. Far-reaching analogies to the physics of atoms, nuclei or metal clusters were obvious from the very beginning: The concepts of shell structure and Hund's rules were found to apply -- just as in real atoms! In this Letter, we report the discovery that electrons confined in ring-shaped quantum dots form rather rigid molecules with antiferromagnetic order in the ground state. This can be seen best from an analysis of the rotational and vibrational excitations

Pade approximants for the ground-state energy of closed-shell quantum dots

Analytic approximations to the ground-state energy of closed-shell quantum dots (number of electrons from 2 to 210) are presented in the form of two-point Pade approximants. These Pade approximants are constructed from the small- and large-density limits of the energy. We estimated that the maximum error, reached for intermediate densities, is less than 3%. Within the present approximation the ground-state is found to be unpolarized.Comment: 4 pages, RevTeX, 3 ps figure

Order-disorder transition in nanoscopic semiconductor quantum rings

Using the path integral Monte Carlo technique we show that semiconductor quantum rings with up to six electrons exhibit a temperature, ring diameter, and particle number dependent transition between spin ordered and disordered Wigner crystals. Due to the small number of particles the transition extends over a broad temperature range and is clearly identifiable from the electron pair correlation functions.Comment: 4 pages, 5 figures, For recent information on physics of small systems see http://www.smallsystems.d

Predictors of employment in young adults with psychiatric work disability

AIM: Mental disorders are the leading cause of work disability among young adults in the industrialized world. Factors predicting employment after long-term psychiatric work disability are largely unknown. METHODS: We linked personal and clinical information from the benefit applications and medical certificates of 1163 young adults (18-34 years) with a new-onset fixed-term psychiatric disability pension in 2008 with employment records between 2005 and 2013. The outcomes were starting employment during and being employed at the end of follow-up. RESULTS: Of the participants, 48% had been employed during and 22% were employed at the end of follow-up. Sustained employment history, university education (master's degree) and no recorded psychological symptoms in childhood were associated with both subsequent employment outcomes. Women and participants under 25 years were more likely to start employment. Depression and other mental disorders (vs psychotic diagnose) and having no comorbid mental disorders or substance abuse were associated with employment at the end of follow-up. CONCLUSIONS: Sustained employment history, university education and no recorded psychological symptoms during childhood predict a return to employment among young adults after a fixed-term psychiatric work disability pension. Pro-active interventions in psychological problems during childhood could enhance employment after a period of work disability

Prediction of neo-adjuvant chemotherapy response in bladder cancer : the impact of clinical parameters and routine biomarkers

Purpose To investigate the role of clinical parameters and immunohistochemical (IHC) biomarkers in their feasibility to predict the effect of neo-adjuvant chemotherapy (NAC) in patients with muscle-invasive urothelial bladder cancer (MIBC). Materials and methods The first 76 consecutive patients with MIBC treated with NAC and radical cystectomy in two University hospitals in Finland between 2008 and 2013 were chosen for this study. After excluding patients with non-urothelial cancer, less than two cycles of chemotherapy, no tissue material for IHC analysis or non-muscle-invasive bladder cancer in re-review, 59 patients were included in the final analysis. A tissue microarray block was constructed from the transurethral resection samples and IHC stainings of Ki-67, p53, Her-2 and EGFR were made. The correlations between histological features in transurethral resection samples and immune-histochemical stainings were calculated. The associations of clinicopathological parameters and IHC stainings with NAC response were evaluated. Factors affecting survival were estimated. Results The complete response rate after NAC was 44%. A higher number of chemotherapy cycles was associated with better response to neo-adjuvant chemotherapy. No response to neo-adjuvant chemotherapy and female gender was associated with decreased cancer-specific survival. The IHC stainings used failed to show an association with neo-adjuvant chemotherapy response and overall or cancer specific survival. Conclusions Patients who do not respond to neo-adjuvant chemotherapy do significantly worse than responders. This study could not find clinical tools to distinguish responders from non-responders. Further studies preferably with larger cohorts addressing this issue are warranted to improve the selection of patients for neo-adjuvant chemotherapy.Peer reviewe

Hartree-Fock dynamics in highly excited quantum dots

Time-dependent Hartree-Fock theory is used to describe density oscillations of symmetry-unrestricted two-dimensional nanostructures. In the small amplitude limit the results reproduce those obtained within a perturbative approach such as the linearized time-dependent Hartree-Fock one. The nonlinear regime is explored by studying large amplitude oscillations in a non-parabolic potential, which are shown to introduce a strong coupling with internal degrees of freedom. This excitation of internal modes, mainly of monopole and quadrupole character, results in sizeable modifications of the dipole absorption.Comment: 4 pages, 4 embedded figure