Interplay between nanometer-scale strain variations and externally applied strain in graphene

We present a molecular modeling study analyzing nanometer-scale strain variations in graphene as a function of externally applied tensile strain. We consider two different mechanisms that could underlie nanometer-scale strain variations: static perturbations from lattice imperfections of an underlying substrate and thermal fluctuations. For both cases we observe a decrease in the out-of-plane atomic displacements with increasing strain, which is accompanied by an increase in the in-plane displacements. Reflecting the non-linear elastic properties of graphene, both trends together yield a non-monotonic variation of the total displacements with increasing tensile strain. This variation allows to test the role of nanometer-scale strain variations in limiting the carrier mobility of high-quality graphene samples

High speed collision and reconnection of Abelian Higgs strings in the deep type-II regime

We study high speed collision and reconnection of cosmic strings in the type-II regime (scalar-to-gauge mass ratios larger than one) of the Abelian Higgs model. New phenomena such as multiple reconnections and clustering of small scale structure have been observed and reported in a previous paper, as well as the fact that the previously observed loop that mediates the second intercommutation is only a loop for sufficiently large beta = m_scalar^2/m_gauge^2. Here we give a more detailed account of our study, involving 3D numerical simulations with beta in the range 1 to 64, the largest value simulated to date, as well as 2D simulations of vortex-antivortex (v-av) collisions to understand the possible relation to the new 3D phenomena. Our simulations give further support to the idea that Abelian Higgs strings never pass through each other, unless this is the result of a double reconnection; and that the critical velocity (v_c) for double reconnection goes down with increasing mass ratio, but energy conservation suggests a lower bound around 0.77c. We discuss the qualitative change in the intermediate state observed for large mass ratios. We relate it to a similar change in the outcome of 2D v-av collisions in the form of radiating bound states. In the deep type-II regime the angular dependence of v_c for double reconnection does not seem to conform to semi-analytic predictions based on the Nambu-Goto approximation. We model the high angle collisions reasonably well by incorporating the effect of core interactions, and the torque they produce on the approaching strings, into the Nambu-Goto description of the collision. An interesting, counterintuitive aspect is that the effective collision angle is smaller because of the torque. Our results suggest differences in network evolution and radiation output with respect to the predictions based on Nambu-Goto or beta = 1 Abelian Higgs dynamics.Comment: 13 pages, 7 figures Send For Publication in Physics Review

Limits on the Mass, Velocity and Orbit of PSR J1933−-6211

We present a high-precision timing analysis of PSR J1933$-$6211, a millisecond pulsar (MSP) with a 3.5-ms spin period and a white dwarf (WD) companion, using data from the Parkes radio telescope. Since we have accurately measured the polarization properties of this pulsar we have applied the matrix template matching approach in which the times of arrival are measured using full polarimetric information. We achieved a weighted root-mean-square timing residuals (rms) of the timing residuals of 1.23 $\rm \mu s$, 15.5$\%$ improvement compared to the total intensity timing analysis. After studying the scintillation properties of this pulsar we put constraints on the inclination angle of the system. Based on these measurements and on $\chi^2$ mapping we put a 2-$\sigma$ upper limit on the companion mass (0.44 M$_\odot$). Since this mass limit cannot reveal the nature of the companion we further investigate the possibility of the companion to be a He WD. Applying the orbital period-mass relation for such WDs, we conclude that the mass of a He WD companion would be about 0.26$\pm$0.01 M$_\odot$ which, combined with the measured mass function and orbital inclination limits, would lead to a light pulsar mass $\leqslant$ 1.0 M$_\odot$. This result seems unlikely based on current neutron star formation models and we therefore conclude that PSR J1933$-$6211 most likely has a CO WD companion, which allows for a solution with a more massive pulsar

On detection of the stochastic gravitational-wave background using the Parkes pulsar timing array

We search for the signature of an isotropic stochastic gravitational-wave background in pulsar timing observations using a frequency-domain correlation technique. These observations, which span roughly 12 yr, were obtained with the 64-m Parkes radio telescope augmented by public domain observations from the Arecibo Observatory. A wide range of signal processing issues unique to pulsar timing and not previously presented in the literature are discussed. These include the effects of quadratic removal, irregular sampling, and variable errors which exacerbate the spectral leakage inherent in estimating the steep red spectrum of the gravitational-wave background. These observations are found to be consistent with the null hypothesis, that no gravitational-wave background is present, with 76 percent confidence. We show that the detection statistic is dominated by the contributions of only a few pulsars because of the inhomogeneity of this data set. The issues of detecting the signature of a gravitational-wave background with future observations are discussed.Comment: 12 pages, 8 figures, 7 tables, accepted for publication in MNRA

Deep XMM-Newton Spectroscopic and Timing Observations of the Isolated Radio Millisecond Pulsar PSR J0030+0451

We present deep XMM-Newton EPIC spectroscopic and timing X-ray observations of the nearby solitary radio millisecond pulsar, PSR J0030+0451. Its emission spectrum in the 0.1-10 keV range is found to be remarkably similar to that of the nearest and best studied millisecond pulsar, PSR J0437-4715, being well described by a predominantly thermal two-temperature model plus a faint hard tail evident above ~2 keV. The pulsed emission in the 0.3-2 keV band is characterized by two broad pulses with pulsed fraction ~60-70%, consistent with a mostly thermal origin of the X-rays only if the surface polar cap radiation is from a light-element atmosphere. Modeling of the thermal pulses permits us to place constraints on the neutron star radius of R>10.7 (95% confidence) and R>10.4 km (at 99.9% confidence) for M=1.4 M_sun.Comment: 8 pages, 7 figures; accepted for publication in The Astrophysical Journa

Collective learning in schools described: building collective learning capacity

Processes of collective learning are expected to increase the professionalism of teachers and school leaders. Little is known about the processes of collective learning which take place in schools and about the way in which those processes may be improved. This paper describes a research into processes of collective learning at three primary schools. Processes of collective learning are described which took place in small teams in these schools. It is also pointed out which attempts can be made in order to reinforce these processes in the schools mentioned

Isotopic analysis of Solenopsis geminata diets in invaded Indonesian savanna.

OBJECTIVE: To examine the extent to which smokers express negative statements about quitting and the extent to which these statements influence general practitioners' (GPs') and practice nurses' (PNs') (dis)continuation of guideline-recommended smoking cessation care. METHODS: Fifty-two video-consultations were observed (GP-consultations: 2007-2008; PN-consultations: 2010-2011). Dialogues were transcribed verbatim and professionals' and patients' speech units were coded and analysed using sequential analyses (n=1424 speech units). RESULTS: GPs focused on asking about smoking (GPs: 42.4% versus PNs: 26.2%, p=0.011) and advising them to quit (GPs: 15.3% versus PNs: 3.5%, p<0.001), whereas PNs focused on assisting them with quitting (GPs: 25.4% versus PNs: 55.2%, p<0.001). Overall, patients expressed more negative statements about quitting than positive statements (negative: 25.3% versus positive: 11.9%, p<0.001), especially when PNs assessed their willingness to quit (OR 3.61, 95% CI 1.44-9.01) or assisted them with quitting (OR 2.23, 95% CI 1.43-3.48). PRACTICE IMPLICATIONS: An alternative approach to smoking cessation care is proposed in which GPs' tasks are limited to asking, advising, and arranging follow-up. This approach seems the least likely to evoke negative statements of patients about quitting during dialogues with GPs and is compatible with the tasks and skills of PNs who could, subsequently, assist smokers with quitting

The Academic Collaborative Center Older Adults:A description of co-creation between science, care practice and education with the aim to contribute to person-centered care for older adult

Long-term care for older adults is in transition. Organizations offering long-term care for older adults are expected to provide person-centered care (PCC) in a complex context, with older adults aging in place and participating in society for as long as possible, staff shortages and the slow adoption of technological solutions. To address these challenges, these organizations increasingly use scientific knowledge to evaluate and innovate long-term care. This paper describes how co-creation, in the sense of close, intensive, and equivalent collaboration between science, care practice, and education, is a key factor in the success of improving long-term care for older adults. Such co-creation is central in the Academic Collaborative Center (ACC) Older Adults of Tilburg University. In this ACC, Tilburg University has joined forces with ten organizations that provide care for older adults and CZ zorgkantoor to create both scientific knowledge and societal impact in order to improve the quality of person-centered care for older adults. In the Netherlands, a “zorgkantoor” arranges long-term (residential) care on behalf of the national government. A zorgkantoor makes agreements on cost and quality with care providers and helps people that are in need of care to decide what the best possible option in their situation is. The CZ zorgkantoor arranges the long-term (residential) care in the south and southwest of the Netherlands. This paper describes how we create scientific knowledge to contribute to the knowledge base of PCC for older adults by conducting social scientific research in which the perspectives of older adults are central. Subsequently, we show how we create societal impact by facilitating and stimulating the use of our scientific knowledge in daily care practice. In the closing section, our ambitions for the future are discussed