2,327 research outputs found
Ferromagnetic Luttinger Liquids
We study weak itinerant ferromagnetism in one-dimensional Fermi systems using
perturbation theory and bosonization. We find that longitudinal spin
fluctuations propagate ballistically with velocity v_m << v_F, where v_F is the
Fermi velocity. This leads to a large anomalous dimension in the spin-channel
and strong algebraic singularities in the single-particle spectral function and
in the transverse structure factor for momentum transfers q ~ 2 Delta/v_F,
where 2 Delta is the exchange splitting.Comment: 4 pages, 3 figure
Dynamical steady states in driven quantum systems
We derive dynamical equations for a driven, dissipative quantum system in which the environment-induced relaxation rate is comparable to the Rabi frequency, avoiding assumptions on the frequency dependence of the environmental coupling. When the environmental coupling varies significantly on the scale of the Rabi frequency, secular or rotating wave approximations break down. We avoid these approximations, yielding dynamical steady states which account for the interaction between driven quantum dots and their phonon environment. The theory, which is motivated by recent experimental observations, qualitatively and quantitatively describes the transition from asymmetric unsaturated resonances at weak driving to population inversion at strong driving
The role of transposable elements in health and diseases of the central nervous system
First discovered in maize by Barbara McClintock in the 1940s, transposable elements (TEs) are DNA sequences that in some cases have the ability to move along chromosomes or "transpose" in the genome. This revolutionary finding was initially met with resistance by the scientific community and viewed by some as heretical. A large body of knowledge has accumulated over the last 60 years on the biology of TEs. Indeed, it is now known that TEs can generate genomic instability and reconfigure gene expression networks both in the germline and somatic cells. This review highlights recent findings on the role of TEs in health and diseases of the CNS, which were presented at the 2013 Society for Neuroscience meeting. The work of the speakers in this symposium shows that TEs are expressed and active in the brain, challenging the dogma that neuronal genomes are static and revealing that they are susceptible to somatic genomic alterations. These new findings on TE expression and function in the CNS have major implications for understanding the neuroplasticity of the brain, which could hypothetically have a role in shaping individual behavior and contribute to vulnerability to disease
Harnessing nuclear spin polarization fluctuations in a semiconductor nanowire
Soon after the first measurements of nuclear magnetic resonance (NMR) in a
condensed matter system, Bloch predicted the presence of statistical
fluctuations proportional to in the polarization of an ensemble of
spins. First observed by Sleator et al., so-called "spin noise" has
recently emerged as a critical ingredient in nanometer-scale magnetic resonance
imaging (nanoMRI). This prominence is a direct result of MRI resolution
improving to better than 100 nm^3, a size-scale in which statistical spin
fluctuations begin to dominate the polarization dynamics. We demonstrate a
technique that creates spin order in nanometer-scale ensembles of nuclear spins
by harnessing these fluctuations to produce polarizations both larger and
narrower than the natural thermal distribution. We focus on ensembles
containing ~10^6 phosphorus and hydrogen spins associated with single InP and
GaP nanowires (NWs) and their hydrogen-containing adsorbate layers. We monitor,
control, and capture fluctuations in the ensemble's spin polarization in
real-time and store them for extended periods. This selective capture of large
polarization fluctuations may provide a route for enhancing the weak magnetic
signals produced by nanometer-scale volumes of nuclear spins. The scheme may
also prove useful for initializing the nuclear hyperfine field of electron spin
qubits in the solid-state.Comment: 18 pages, 5 figure
Charge-based quantum computing using single donors in semiconductors
Solid-state quantum computer architectures with qubits encoded using single
atoms are now feasible given recent advances in atomic doping of
semiconductors. Here we present a charge qubit consisting of two dopant atoms
in a semiconductor crystal, one of which is singly ionised. Surface electrodes
control the qubit and a radio-frequency single electron transistor provides
fast readout. The calculated single gate times, of order 50ps or less, are much
shorter than the expected decoherence time. We propose universal one- and
two-qubit gate operations for this system and discuss prospects for fabrication
and scale up.Comment: 5 pages, 4 figures, updated version submitted to Physical Review
Different expressions of the same mode: a recent dialogue between archaeological and contemporary drawing practices
In this article we explore what we perceive as pertinent features of shared experience at the excavations of an Iron Age Hillfort at Bodfari, North Wales, referencing artist, archaeologist and examples of seminal art works and archaeological records resulting through inter-disciplinary collaboration. We explore ways along which archaeological and artistic practices of improvisation become entangled and productive through their different modes of mark-making. We contend that marks and memories of artist and archaeologist alike emerge interactively, through the mutually constituting effects of the object of study, the tools of exploration, and the practitioners themselves, when they are enmeshed in the cross-modally bound activities. These include, but are not limited to, remote sensing, surveying, mattocking, trowelling, drawing, photographing, videoing and sound recording. These marks represent the co-signatories: the gesture of the often anonymous practitioners, the voice of the deposits, as well as the imprint of the tools, and their interplay creates a multi-threaded narrative documenting their modes of intra-action, in short our practices. They occupy the conceptual space of paradata, and in the process of saturating the interstices of digital cognitive prosthetics they lend probity to their translations in both art form and archive
Positive words carry less information than negative words
We show that the frequency of word use is not only determined by the word
length \cite{Zipf1935} and the average information content
\cite{Piantadosi2011}, but also by its emotional content. We have analyzed
three established lexica of affective word usage in English, German, and
Spanish, to verify that these lexica have a neutral, unbiased, emotional
content. Taking into account the frequency of word usage, we find that words
with a positive emotional content are more frequently used. This lends support
to Pollyanna hypothesis \cite{Boucher1969} that there should be a positive bias
in human expression. We also find that negative words contain more information
than positive words, as the informativeness of a word increases uniformly with
its valence decrease. Our findings support earlier conjectures about (i) the
relation between word frequency and information content, and (ii) the impact of
positive emotions on communication and social links.Comment: 16 pages, 3 figures, 3 table
Feasibility of telephone-delivered therapy for common mental health difficulties embedded in paediatric epilepsy clinics
Background:
Mental and physical health treatment should be delivered together for children and young people with epilepsy. Training healthcare professionals (HCPs) in epilepsy services to deliver mental health interventions is an important way to facilitate integrated care.
Objective:
To determine the feasibility of remotely delivered assessment and psychological treatment for mental health difficulties delivered by HCPs in pediatric epilepsy clinics with limited formal training in psychological interventions. We hypothesized that it would be (i) feasible to train HCPs to deliver the psychological intervention and (ii) that participants receiving the psychological therapy would report reductions in symptoms of mental health difficulties including anxiety, depression, and behavior difficulties and improve quality of life.
Methods:
Thirty-four children and young people with epilepsy who had impairing symptoms of a common mental health difficulty (anxiety, depression, disruptive behavior, and/or trauma) were allocated to receive 6 months of a modular cognitive behavioral intervention delivered by a HCP with limited formal psychological therapy experience. Thirteen HCPs were trained in delivery of the intervention. Healthcare professional competence was assessed in a two-stage process. Parent-reported measures of mental health symptoms and quality of life were completed at baseline and following the intervention. Paired t-tests were used to analyze changes in symptoms over time.
Results:
All thirteen HCPs who participated in the training were considered competent in therapeutic delivery by the end of the training period. Twenty-three patients completed pre- and post-intervention measures and were included in the analysis. There were statistically significant improvements in: symptoms of mental health problems (p = 0.01; Cohen’s d = 0.62), total impact of mental health problems (p = 0.03; Cohen’s d = 0.52), anxiety and depression symptoms (p = 0.02; Cohen’s d = 0.57) and quality of life (p = 0.01; Cohen’s d = 0.57).
Conclusion:
A modular cognitive behavioral treatment delivered over the telephone by HCPs with limited experience of psychological therapy was feasible and effective in treating mental health problems in children and young people with epilepsy. Health-related Quality of Life also improved over the duration of treatment. A randomized controlled trial (RCT) is needed to demonstrate efficacy of the intervention
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