6,502 research outputs found
The NIR structure of the barred galaxy NGC253 from VISTA
[abridged] We used J and Ks band images acquired with the VISTA telescope as
part of the science verification to quantify the structures in the stellar disk
of the barred Sc galaxy NGC253. Moving outward from the galaxy center, we find
a nuclear ring within the bright 1 kpc diameter nucleus, then a bar, a ring
with 2.9 kpc radius. From the Ks image we obtain a new measure of the
deprojected length of the bar of 2.5 kpc. The bar's strength, as derived from
the curvature of the dust lanes in the J-Ks image, is typical of weak bars.
From the deprojected length of the bar, we establish the corotation radius
(R_CR=3 kpc) and bar pattern speed (Omega_b = 61.3 km /s kpc), which provides
the connection between the high-frequency structures in the disk and the
orbital resonances induced by the bar. The nuclear ring is located at the inner
Lindblad resonance. The second ring does not have a resonant origin, but it
could be a merger remnant or a transient structure formed during an
intermediate stage of the bar formation. The inferred bar pattern speed places
the outer Lindblad resonance within the optical disk at 4.9 kpc, in the same
radial range as the peak in the HI surface density. The disk of NGC253 has a
down-bending profile with a break at R~9.3 kpc, which corresponds to about 3
times the scale length of the inner disk. We discuss the evidence for a
threshold in star formation efficiency as a possible explanation of the steep
gradient in the surface brightness profile at large radii. The NIR photometry
unveils the dynamical response of the NGC253 stellar disk to its central bar.
The formation of the bar may be related to the merger event that determined the
truncation of stars and gas at large radii and the perturbation of the disk's
outer edge.Comment: Accepted for publication in Astronomy & Astrphysics. High resolution
pdf file is available at the following link:
https://www.dropbox.com/s/4o4cofs1lyjrtpv/NGC253.pd
Efficient Symmetry Reduction and the Use of State Symmetries for Symbolic Model Checking
One technique to reduce the state-space explosion problem in temporal logic
model checking is symmetry reduction. The combination of symmetry reduction and
symbolic model checking by using BDDs suffered a long time from the
prohibitively large BDD for the orbit relation. Dynamic symmetry reduction
calculates representatives of equivalence classes of states dynamically and
thus avoids the construction of the orbit relation. In this paper, we present a
new efficient model checking algorithm based on dynamic symmetry reduction. Our
experiments show that the algorithm is very fast and allows the verification of
larger systems. We additionally implemented the use of state symmetries for
symbolic symmetry reduction. To our knowledge we are the first who investigated
state symmetries in combination with BDD based symbolic model checking
Randomized benchmarking of single and multi-qubit control in liquid-state NMR quantum information processing
Being able to quantify the level of coherent control in a proposed device
implementing a quantum information processor (QIP) is an important task for
both comparing different devices and assessing a device's prospects with
regards to achieving fault-tolerant quantum control. We implement in a
liquid-state nuclear magnetic resonance QIP the randomized benchmarking
protocol presented by Knill et al (PRA 77: 012307 (2008)). We report an error
per randomized pulse of with a
single qubit QIP and show an experimentally relevant error model where the
randomized benchmarking gives a signature fidelity decay which is not possible
to interpret as a single error per gate. We explore and experimentally
investigate multi-qubit extensions of this protocol and report an average error
rate for one and two qubit gates of for a three
qubit QIP. We estimate that these error rates are still not decoherence limited
and thus can be improved with modifications to the control hardware and
software.Comment: 10 pages, 6 figures, submitted versio
Experimental effects of mindfulness inductions on self-regulation: Systematic review and meta-analysis.
Self-regulation is the control of aspects of the self to allow pursuit of long-term goals, and it is proposed as a central pathway through which mindfulness may exert benefits on well-being. However, the effects of a single mindfulness induction on self-regulation are not clear, as there has been no comprehensive review of this evidence. The current review synthesized existing findings relating to the effect of a mindfulness induction delivered in a laboratory setting on measures of self-regulation. Twenty-seven studies were included and grouped according to 3 outcomes: regulation of experimentally induced negative affect (k = 15; meta-analysis), emotion-regulation strategies (k = 7) and executive functions (k = 9; narrative synthesis). A mindfulness induction was superior to comparison groups in enhancing the regulation of negative affect (d = -.28). Executive-function performance was enhanced only when the experimental design included an affect induction or when the outcome was sustained attention. The effect on emotion-regulation strategies was inconclusive, but with emerging evidence for an effect on rumination. Overall, the findings indicate that, in the form of an induction, mindfulness may have the most immediate effect on attention mechanisms rather than exerting cognitive changes in other domains, as are often reported outcomes of longer mindfulness training. Through effecting change in attention, emotion regulation of negative affect can be enhanced, and subsequently, executive-function performance more quickly restored. The interpretations of the findings are caveated with consideration of the low quality of many of the included study designs determined by the quality appraisal tool
A systematic review of the role of parents in the development of anxious cognitions in children
Anxious cognitions and parental behavior are important in the development of child anxiety. The current review aims to appraise the literature on the relationship between parental factors and chid anxious cognitions. Online database searches of PsycInfo, Scopus, ProQuest Dissertations and Web of Science were systematically searched using key terms related to 'parent', 'child', 'anxiety' and 'cognitions'. Included studies (N = 13) were quality assessed and study findings were appraised in line with cognitive behavioral frameworks of the parental pathways to the development of anxious cognitions in children. Reviewed studies confirmed that parental factors have a role in the development of their children's anxious cognitions by modelling fearful responses, reducing their child's autonomy, and indirectly via their own expectations about their child. Limitations of the literature are considered, including issues of measurement. Future research should consider multi-modal assessment of parental factors and examine parental behavior and child anxious cognitions in the context of real-life threatening events
Model Checking CTL is Almost Always Inherently Sequential
The model checking problem for CTL is known to be P-complete (Clarke,
Emerson, and Sistla (1986), see Schnoebelen (2002)). We consider fragments of
CTL obtained by restricting the use of temporal modalities or the use of
negations---restrictions already studied for LTL by Sistla and Clarke (1985)
and Markey (2004). For all these fragments, except for the trivial case without
any temporal operator, we systematically prove model checking to be either
inherently sequential (P-complete) or very efficiently parallelizable
(LOGCFL-complete). For most fragments, however, model checking for CTL is
already P-complete. Hence our results indicate that, in cases where the
combined complexity is of relevance, approaching CTL model checking by
parallelism cannot be expected to result in any significant speedup. We also
completely determine the complexity of the model checking problem for all
fragments of the extensions ECTL, CTL+, and ECTL+
United Kingdom: Citizenship education in the United Kingdom: comparing England, Northern Ireland, Scotland and Wales
Purpose: In this country case study the authors undertake a comparative analysis of citizenship education across the four nations of the UK. The curriculum and contexts in England, Scotland, Wales and Northern Ireland are first described. Then the article considers how each national example engages with fundamental expectations of citizenship education, specifically in relation to questions of citizenship status and the relationship between citizens and the state; political identity; and active citizenship processes.
Approach: Drawing on the authors’ collective experience and insights into policy and practice in each nation, we started with a ‘generative conversation’ to identify key issues for inclusion in this case study.
Findings: The article unearths a variety of constraints and problems, and situates these in a broader policyscape in which policy accretion and policy approximation generate a permissive culture, which has undermined the promise of citizenship education as an entitlement for all young people
Frequentist Evaluation of Group Sequential Clinical Trial Designs
Group sequential stopping rules are often used as guidelines in the monitoring of clinical trials in order to address the ethical and efficiency issues inherent in human testing of a new treatment or preventive agent for disease. Such stopping rules have been proposed based on a variety of different criteria, both scientific (e.g., estimates of treatment effect) and statistical (e.g., frequentist type I error, Bayesian posterior probabilities, stochastic curtailment). It is easily shown, however, that a stopping rule based on one of those criteria induces a stopping rule on all other criteria. Thus the basis used to initially define a stopping rule is relatively unimportant so long as the operating characteristics of the stopping rule are fully investigated. In this paper we describe how the frequentist operating characteristics of a particular stopping rule might be evaluated in order to ensure that the selected clinical trial design satisfies the constraints imposed by the many different disciplines represented by the clinical trial collaborators
Bayesian Evaluation of Group Sequential Clinical Trial Designs
Clincal trial designs often incorporate a sequential stopping rule to serve as a guide in the early termination of a study. When choosing a particular stopping rule, it is most common to examine frequentist operating characteristics such as type I error, statistical power, and precision of confi- dence intervals (Emerson, et al. [1]). Increasingly, however, clinical trials are designed and analyzed in the Bayesian paradigm. In this paper we describe how the Bayesian operating characteristics of a particular stopping rule might be evaluated and communicated to the scientific community. In particular, we consider a choice of probability models and a family of prior distributions that allows concise presentation of Bayesian properties for a specified sampling plan
Information-theoretic equilibration: the appearance of irreversibility under complex quantum dynamics
The question of how irreversibility can emerge as a generic phenomena when
the underlying mechanical theory is reversible has been a long-standing
fundamental problem for both classical and quantum mechanics. We describe a
mechanism for the appearance of irreversibility that applies to coherent,
isolated systems in a pure quantum state. This equilibration mechanism requires
only an assumption of sufficiently complex internal dynamics and natural
information-theoretic constraints arising from the infeasibility of collecting
an astronomical amount of measurement data. Remarkably, we are able to prove
that irreversibility can be understood as typical without assuming decoherence
or restricting to coarse-grained observables, and hence occurs under distinct
conditions and time-scales than those implied by the usual decoherence point of
view. We illustrate the effect numerically in several model systems and prove
that the effect is typical under the standard random-matrix conjecture for
complex quantum systems.Comment: 15 pages, 7 figures. Discussion has been clarified and additional
numerical evidence for information theoretic equilibration is provided for a
variant of the Heisenberg model as well as one and two-dimensional random
local Hamiltonian
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