8,518 research outputs found
Spiral order by disorder and lattice nematic order in a frustrated Heisenberg antiferromagnet on the honeycomb lattice
Motivated by recent experiments on BiMnO(NO), we study a
frustrated - Heisenberg model on the two dimensional (2D) honeycomb
lattice. The classical - Heisenberg model on the two dimensional (2D)
honeycomb lattice has N\'eel order for , it
exhibits a one-parameter family of degenerate incommensurate spin spiral ground
states where the spiral wave vector can point in any direction. Spin wave
fluctuations at leading order lift this accidental degeneracy in favor of
specific wave vectors, leading to spiral order by disorder. For spin ,
quantum fluctuations are, however, likely to be strong enough to melt the
spiral order parameter over a wide range of . Over a part of this
range, we argue that the resulting state is a valence bond solid (VBS) with
staggered dimer order - this VBS is a nematic which breaks lattice rotational
symmetry. Our arguments are supported by comparing the spin wave energy with
the energy of the dimer solid obtained using a bond operator formalism. Turning
to the effect of thermal fluctuations on the spiral ordered state, any nonzero
temperature destroys the magnetic order, but the discrete rotational symmetry
of the lattice remains broken resulting in a thermal analogue of the nematic
VBS. We present arguments, supported by classical Monte Carlo simulations, that
this nematic transforms into the high temperature symmetric paramagnet via a
thermal phase transition which is in the universality class of the classical
3-state Potts (clock) model in 2D. We discuss the possible relevance of our
results for honeycomb magnets, such as BiMO(NO) (with
M=Mn,V,Cr), and bilayer triangular lattice magnets.Comment: Slightly revise
Status of National Open Spatial Data Infrastructures: a Comparison Across Continents
The increasing need for geospatial information demands for well-organised management among all levels of society. A Spatial Data Infrastructure (SDI) is a multidisciplinary and dynamic instrument that facilitates access and sharing of geospatial information. The current trend towards open data initiatives is influencing the development of these infrastructures. In order to examine this effect, this article addresses the following question: what is the current state of SDI openness of four best practice open data countries Canada, The Netherlands, Australia and Brazil, and how do they compare? The question is answered through a qualitative literature study and the application of a newly developed Open SDI Assessment Framework to the countries. The Netherlands and Canada show a high performance on all assessment dimensions; data discovery, data access and data properties. Australia and Brazil show a poor open SDI performance, as they could not meet the requirements set for the assessed datasets. General conclusions of the assessment are that data is currently fragmented and scattered among the web in all four countries, which strongly negatively influences the user experience. It is crucial that a strict legal framework is embedded in a country, which ensures that current SDI objectives and propositions regarding an user-centred approach and open data availability are achieved
Selection for uniformity in livestock by exploiting genetic heterogeneity of residual variance
In some situations, it is worthwhile to change not only the mean, but also the variability of traits by selection. Genetic variation in residual variance may be utilised to improve uniformity in livestock populations by selection. The objective was to investigate the effects of genetic parameters, breeding goal, number of progeny per sire and breeding scheme on selection responses in mean and variance when applying index selection. Genetic parameters were obtained from the literature. Economic values for the mean and variance were derived for some standard non-linear profit equations, e.g. for traits with an intermediate optimum. The economic value of variance was in most situations negative, indicating that selection for reduced variance increases profit. Predicted responses in residual variance after one generation of selection were large, in some cases when the number of progeny per sire was at least 50, by more than 10% of the current residual variance. Progeny testing schemes were more efficient than sib-testing schemes in decreasing residual variance. With optimum traits, selection pressure shifts gradually from the mean to the variance when approaching the optimum. Genetic improvement of uniformity is particularly interesting for traits where the current population mean is near an intermediate optimum
Vocational perspectives after spinal cord injury
Objective: To give insight into the vocational situation several years after a traumatic spinal cord injury (SCI) and describe the personal experiences and unmet needs; to give an overview of health and functional status per type of SCI and their relationship with employment status. Design: Descriptive analysis of data from a questionnaire. Setting: Dutch rehabilitation centre with special department for patients with spinal cord injuries. Subjects: Fifty-seven patients with a traumatic SCI, aged 18-60 years, admitted to the rehabilitation centre from 1990 to 1998. Main measures: Questionnaire with items related to vocational outcome, job experiences, health and functional status. Results: Of 49 patients who were working at the moment of SCI 60% currently had a paid job. Vocational outcome was related to a higher educational level. A significant relation between the SCI-specific health and functional status and employment was not found. The respondents who changed to a new employer needed more time to resume work, but seemed more satisfied with the job and lost fewer working hours than those who resumed work with the same employer. In spite of reasonable to good satisfaction with the current work situation, several negative experiences and unmet needs were reported. Conclusions: Despite a high participation in paid work following SCI, the effort of the disabled worker to have and keep a job should not be underestimated
Source analysis of electrical and magnetic brain responses associated with selective attention and language processing
Density Waves Inside Inner Lindblad Resonance: Nuclear Spirals in Disk Galaxies
We analyze formation of grand-design two-arm spiral structure in the nuclear
regions of disk galaxies. Such morphology has been recently detected in a
number of objects using high-resolution near-infrared observations. Motivated
by the observed (1) continuity between the nuclear and kpc-scale spiral
structures, and by (2) low arm-interarm contrast, we apply the density wave
theory to explain the basic properties of the spiral nuclear morphology. In
particular, we address the mechanism for the formation, maintenance and the
detailed shape of nuclear spirals. We find, that the latter depends mostly on
the shape of the underlying gravitational potential and the sound speed in the
gas. Detection of nuclear spiral arms provides diagnostics of mass distribution
within the central kpc of disk galaxies. Our results are supported by 2D
numerical simulations of gas response to the background gravitational potential
of a barred stellar disk. We investigate the parameter space allowed for the
formation of nuclear spirals using a new method for constructing a
gravitational potential in a barred galaxy, where positions of resonances are
prescribed.Comment: 18 pages, 9 figures, higher resolution available at
http://www.pa.uky.edu/~ppe/papers/nucsp.ps.g
Regulatory Uncertainty and Opportunity Seeking: The Case of Clean Development
Regulatory uncertainty has been inherent to climate change in the absence of a successor to the Kyoto Protocol and with ongoing policy discussions on how to proceed. To facilitate steps to help address the issue, many companies have called for more certainty and a stable policy framework. What has remained underexposed, however, is that, besides having clear disadvantages, regulatory uncertainty may also benefit some companies if they recognize the opportunities of flux and move early. This lack of attention may be due to the fact that disadvantages are easier to pin-point and study than opportunities, also because companies tend to be much more open and explicit in emphasizing problems as they publicly seek political support or financial redress, while keeping strategic opportunities for themselves. Despite these practical difficulties of data collection, the relevance of opportunities related to regulatory uncertainty is very high, for managers but also for policy-makers and academics. To shed some more light on the phenomenon, this article explores regulatory uncertainty and opportunity seeking for the climate change clean development case. It unravels opportunities that have emerged for different types of companies, including utilities, banks, project development & carbon offset companies, brokers, exchanges, consultants, auditors and legal services providers. The article also shows how opportunities have evolved over the years, and have varied for different types of companies, related to fluctuations in the degree of uncertainty and the evolution of clean development projects and the related carbon market
Ultraviolet Signposts of Resonant Dynamics in the Starburst-Ringed Sab Galaxy, M94 (NGC 4736)
M94 (NGC 4736) is investigated using images from the Ultraviolet Imaging
Telescope (FUV-band), Hubble Space Telescope (NUV-band), Kitt Peak 0.9-m
telescope (H-alpha, R, and I bands), and Palomar 5-m telescope (B-band), along
with spectra from the International Ultraviolet Explorer and Lick 1-m
telescopes. The wide-field UIT image shows FUV emission from (a) an elongated
nucleus, (b) a diffuse inner disk, where H-alpha is observed in absorption, (c)
a bright inner ring of H II regions at the perimeter of the inner disk (R = 48
arcsec. = 1.1 kpc), and (d) two 500-pc size knots of hot stars exterior to the
ring on diametrically opposite sides of the nucleus (R= 130 arcsec. = 2.9 kpc).
The HST/FOC image resolves the NUV emission from the nuclear region into a
bright core and a faint 20 arcsec. long ``mini-bar'' at a position angle of 30
deg. Optical and IUE spectroscopy of the nucleus and diffuse inner disk
indicates an approximately 10^7 or 10^8 yr-old stellar population from
low-level starbirth activity blended with some LINER activity. Analysis of the
H-alpha, FUV, NUV, B, R, and I-band emission along with other observed tracers
of stars and gas in M94 indicates that most of the star formation is being
orchestrated via ring-bar dynamics involving the nuclear mini-bar, inner ring,
oval disk, and outer ring. The inner starburst ring and bi-symmetric knots at
intermediate radius, in particular, argue for bar-mediated resonances as the
primary drivers of evolution in M94 at the present epoch. Similar processes may
be governing the evolution of the ``core-dominated'' galaxies that have been
observed at high redshift. The gravitationally-lensed ``Pretzel Galaxy''
(0024+1654) at a redshift of approximately 1.5 provides an important precedent
in this regard.Comment: revised figure 1 (corrected coordinate labels on declination axis);
19 pages of text + 19 figures (jpg files); accepted for publication in A
Innovations and paradigm shifts in atrial fibrillation ablation
Treatment of symptomatic atrial fibrillation has seen important changes in the past decades. Advancements have especially been made in the field of non-pharmacological treatment of this disease. Patients in whom a rhythm control strategy is chosen the place of catheter ablation has become more frontline therapy in the past years. The procedure itself has also seen changes in technologies that can be used, either using point-by-point radiofrequency or one of the single-shot techniques. One of the major limitations that remain is that re-do procedures are often necessary due to incomplete pulmonary vein isolation and/or atrial fibrillation being initiated by other mechanisms than pulmonary vein triggers. Therefore, there is further need for developing ablation tools that reproducibly isolate the pulmonary vein transmurally. Furthermore, addressing the underlying conditions before and after catheter ablation has been shown to be of great importance. In this review, we will give an overview of the evolution of catheter ablation, highlight the latest technologies and their future endeavours, and lifestyle modifications are being discussed as part of the catheter ablation strategy
From Living Apart to Living Together:Do Children Born before the Current Partnership Matter?
This study examines the association between having children born before the current partnership and women’s and men’s likelihood of transitioning from living apart together (LAT) to co-residing. LAT partnerships are common among individuals with pre-partnership children, but have so far been under-researched. Our study not only focuses on those in LAT relations, but also takes the different pathways to becoming a single parent into account. Event-history analysis was performed using waves 1-4 from the Netherlands Kinship Panel Study.
The results indicate that separated and widowed mothers were less likely to transition to co-residence with their LAT partner than childless women who had previously been in a co-residential union. Mothers who had previous out-of-union children were found to be even less likely to enter co-residence. Results were mostly similar for men and women. The only exception was the effect of being widowed with children; for men this resulted in higher chances of transitioning to co-residence with a new partner whereas for women the chances were lower.
The findings suggest that individuals’ parenthood and union histories are associated with the development of their later partnerships, and that these patterns vary by gender. Given contemporary and future patterns of partnership separation, our study provides insights for better understanding how LAT relations develop for different sub-populations
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