Estimates of Effective Hubbard Model Parameters for C20 isomers

We report on an effective Hubbard Hamiltonian approach for the study of electronic correlations in C$_{20}$ isomers, cage, bowl and ring, with quantum Monte Carlo and exact diagonalization methods. The tight-binding hopping parameter, $t$, in the effective Hamiltonian is determined by a fit to density functional theory calculations, and the on-site Coulomb interaction, $U/t$, is determined by calculating the isomers' affinity energies, which are compared to experimental values. For the C$_{20}$ fullerene cage we estimate $t_{\rm cage}\simeq 0.68-1.36$ eV and $(U/t)_{\rm cage} \simeq 7.1-12.2$. The resulting effective Hamiltonian is then used to study the shift of spectral peaks in the density of states of neutral and one-electron-doped C$_{20}$ isomers. Energy gaps are also extracted for possible future comparison with experiments.Comment: 6 pages, 5 figure

Extended Hubbard model on a C20_{20} molecule

The electronic correlations on a C$_{20}$ molecule, as described by an extended Hubbard Hamiltonian with a nearest neighbor Coulomb interaction of strength $V$, are studied using quantum Monte Carlo and exact diagonalization methods. For electron doped C$_{20}$, it is known that pair-binding arising from a purely electronic mechanism is absent within the standard Hubbard model (V=0). Here we show that this is also the case for hole doping for $0<U/t\leq 3$ and that, for both electron and hole doping, the effect of a non-zero $V$ is to work against pair-binding. We also study the magnetic properties of the neutral molecule, and find transitions between spin singlet and triplet ground states for either fixed $U$ or $V$ values. In addition, spin, charge and pairing correlation functions on C$_{20}$ are computed. The spin-spin and charge-charge correlations are very short-range, although a weak enhancement in the pairing correlation is observed for a distance equal to the molecular diameter.Comment: 9 pages, 8 figures, 4 table

Single-particle Excitation Spectra of C60_{60} Molecules and Monolayers

In this paper we present calculations of single-particle excitation spectra of neutral and three-electron-doped Hubbard C$_{60}$ molecules and monolayers from large-scale quantum Monte Carlo simulations and cluster perturbation theory. By a comparison to experimental photoemission, inverse photoemission, and angle-resolved photoemission data, we estimate the intermolecular hopping integrals and the C$_{60}$ molecular orientation angle, finding agreement with recent X-ray photoelectron diffraction (XPD) experiments. Our results demonstrate that a simple effective Hubbard model, with intermediate coupling, $U=4t$, provides a reasonable basis for modeling the properties of C$_{60}$ compounds.Comment: 6 page

The attention network test: a characteristic pattern of deficits in children with ADHD

<p>Abstract</p> <p>Background</p> <p>The Attention Network test (ANT) gives measures of different aspects of the complex process of attention. We ask if children with Attention Deficit Hyperactivity Disorder (ADHD) will show a characteristic pattern of deficits on this test.</p> <p>Methods</p> <p>The sample included 157 children (M = 10 years) who performed the child version of ANT as participants of the Bergen Child Study. Children with an ADHD diagnosis (N = 45) were compared to a group of children with other diagnoses (N = 55) and a group of children without any diagnosis (N = 57).</p> <p>Results</p> <p>The group of children with ADHD showed low accuracy scores and a variable response set, indicating an inattentive response style. No differences were found between the groups on RT and accuracy measures of the alerting, orienting, and conflict networks. A high correlation between full scale IQ (FSIQ) and ANT measures was only found in the ADHD group. When FSIQ score was included as a covariate, the group differences were not statistically significant on any ANT measure.</p> <p>Conclusion</p> <p>The present study showed that accuracy and variability measures rather than measures of the three attention networks conveyed the characteristic pattern of deficits in children with ADHD. The results emphasized the importance of including these measures to extend the sensitivity of the ANT, and the importance of reporting results both with and without FSIQ as a covariate.</p

Dissipative production of a maximally entangled steady state

Entangled states are a key resource in fundamental quantum physics, quantum cryp-tography, and quantum computation [1].To date, controlled unitary interactions applied to a quantum system, so-called "quantum gates", have been the most widely used method to deterministically create entanglement [2]. These processes require high-fidelity state preparation as well as minimizing the decoherence that inevitably arises from coupling between the system and the environment and imperfect control of the system parameters. Here, on the contrary, we combine unitary processes with engineered dissipation to deterministically produce and stabilize an approximate Bell state of two trapped-ion qubits independent of their initial state. While previous works along this line involved the application of sequences of multiple time-dependent gates [3] or generated entanglement of atomic ensembles dissipatively but relied on a measurement record for steady-state entanglement [4], we implement the process in a continuous time-independent fashion, analogous to optical pumping of atomic states. By continuously driving the system towards steady-state, the entanglement is stabilized even in the presence of experimental noise and decoherence. Our demonstration of an entangled steady state of two qubits represents a step towards dissipative state engineering, dissipative quantum computation, and dissipative phase transitions [5-7]. Following this approach, engineered coupling to the environment may be applied to a broad range of experimental systems to achieve desired quantum dynamics or steady states. Indeed, concurrently with this work, an entangled steady state of two superconducting qubits was demonstrated using dissipation [8].Comment: 25 pages, 5 figure

Spatial Frequency Scheduling for Uplink SC-FDMA based Linearly Precoded LTE Multiuser MIMO Systems

This paper investigates the performance of the uplink single carrier (SC) frequency division multiple access (FDMA) based linearly precoded multiuser multiple input multiple output (MIMO) systems with frequency domain packet scheduling. A mathematical expression of the received signal to interference plus noise ratio (SINR) for the studied systems is derived and a utility function based spatial frequency packet scheduling algorithms is investigated. The schedulers are shown to be able to exploit the available multiuser diversity in time, frequency and spatial domains

Mindfulness-based cognitive therapy improves insomnia symptoms in individuals with recurrent depression: secondary analyses from a randomized controlled trial

Background: Embedded within a randomized efficacy trial, the present study aimed to investigate whether mindfulness-based cognitive therapy (MBCT) for recurrent depression improved symptoms of insomnia. Methods: Sixty-eight remitted participants with at least three prior episodes of depression were randomized to 8 weeks of MBCT (n = 33) or a waitlist control condition (n = 35). The Bergen Insomnia Scale was used to screen for insomnia symptoms before and after the intervention. The analyses were conducted using one-way between-groups analyses of covariance. Results: Twenty-five MBCT participants and 30 waitlist controls completed the study (74.5% females; mean age 40.7 ± 12.9 years). At baseline, 83.6% screened positive for the insomnia diagnosis. Following the intervention and after controlling for corresponding insomnia parameters at baseline, MBCT completers reported significantly less severe insomnia symptoms (p = 0.017), as well as less problems with prolonged sleep onset (p = 0.047) and nocturnal awakenings (p = 0.023), relative to controls. No group differences were found on early morning awakening, daytime impairment, or dissatisfaction with sleep. Conclusion: The results suggest that MBCT improves certain insomnia symptoms. However, additional sleep-specific interventions may be needed to further improve this population’s sleep.publishedVersio

Low Persistence of Inattention Symptoms From Childhood to Adolescence: A Population-Based Study

Objective: To investigate the persistence of dimensional measures of inattention in a population-based, gender-balanced sample of adolescents with parent reports of inattention from childhood and self-reports of inattention in adolescence. Method: Adolescents, 16–19 years old, completed the Adult ADHD Self Report Scale. Their parents completed the Swanson, Nolan, and Pelham Rating Scale—4th Edition when they were 7–9 and 11–13 years old. Results: More severe inattention in boys than girls in childhood shifted to a female predominance in adolescence. The correlation between reports of inattention in childhood and adolescence was weak, with parent reports explaining only ~5% of the variance in the inattention score reported in adolescence. Conclusion: The weak association between inattention in childhood and adolescence is consistent with the emerging challenges associated with being an adolescent, but the impact of shifts in informants, gender and age on symtpom presentations should be investigated in future studies.publishedVersio

Goal management training for adults with ADHD – clients’ experiences with a group-based intervention

Background: There is growing evidence for the efficacy of group-based interventions for adults with ADHD. However, there is still a lack of research investigating how clients experience participating in such interventions. The aim of the current study was to explore how adults with ADHD experience participating in a group-based intervention (Goal Management Training) for ADHD. Method: We conducted individual, semi-structured, interviews with ten adults with ADHD who had participated in Goal Management Training administered as a group intervention. The interviews were transcribed verbatim and analyzed using thematic analysis within a hermeneutic phenomenological framework. Results: Our analysis identified three main themes. The participants’ starting point captured the participants’ motivation and expectations prior to treatment. The ambiguity of the group – the various meanings of the group consisted of three sub-themes (The group created a sense of belonging - “I am not alone”; The personal cost of participating in the group - “At times it was a hot mess”; and The group supported the learning experience - “We worked with it together”). The group promoted positive change – How the group affected the participants’ everyday lives consisted of two sub-themes (Managing ADHD in daily life - “It’s much easier to handle everyday life”, and Personal growth - “Gaining new perspectives”). Conclusion: The group format was experienced as a valuable aspect of treatment. The structure provided by Goal Management Training allowed participants to expand their perspectives and experience improved management of ADHD, as well as personal growth. The opportunity to exchange experiences with others in similar situations was seen as particularly beneficial and brought feelings of recognition and belonging. However, some also experienced the group as a burden at times, for instance by stealing one’s focus. This study expands existing knowledge by exploring clients’ experiences of participating in group-based interventions for ADHD and shows how the group format provided participants with more than they had hoped for. While expecting a more instrumental outcome of treatment, such as tools to manage ADHD, participants also gained a welcomed, but unexpected outcome of personal growth.publishedVersio