Laboratory observation of a nonlinear interaction between shear Alfv\'{e}n waves

An experimental investigation of nonlinear interactions between shear Alfv\'{e}n waves in a laboratory plasma is presented. Two Alfv\'{e}n waves, generated by a resonant cavity, are observed to beat together, driving a low frequency nonlinear psuedo-mode at the beat frequency. The psuedo-mode then scatters the Alfv\'{e}n waves, generating a series of sidebands. The observed interaction is very strong, with the normalized amplitude of the driven psuedo-mode comparable to the normalized magnetic field amplitude ($\delta B/B$) of the interacting Alfv\'{e}n waves.Comment: 10 pages, 4 figures, submitted to Phys. Rev. Let

Sharpest possible clustering bounds using robust random graph analysis

Complex network theory crucially depends on the assumptions made about the degree distribution, while fitting degree distributions to network data is challenging, in particular for scale-free networks with power-law degrees. We present a robust assessment of complex networks that does not depend on the entire degree distribution, but only on its mean, range and dispersion: summary statistics that are easy to obtain for most real-world networks. By solving several semi-infinite linear programs, we obtain tight (the sharpest possible) bounds for correlation and clustering measures, for all networks with degree distributions that share the same summary statistics. We identify various extremal random graphs that attain these tight bounds as the graphs with specific three-point degree distributions. We leverage the tight bounds to obtain robust laws that explain how degree-degree correlations and local clustering evolve as function of node degrees and network size. These robust laws indicate that power-law networks with diverging variance are among the most extreme networks in terms of correlation and clustering, building further theoretical foundation for widely reported scale-free network phenomena such as correlation and clustering decay

Regularization of the Hamiltonian constraint and the closure of the constraint algebra

In the paper we discuss the process of regularization of the Hamiltonian constraint in the Ashtekar approach to quantizing gravity. We show in detail the calculation of the action of the regulated Hamiltonian constraint on Wilson loops. An important issue considered in the paper is the closure of the constraint algebra. The main result we obtain is that the Poisson bracket between the regulated Hamiltonian constraint and the Diffeomorphism constraint is equal to a sum of regulated Hamiltonian constraints with appropriately redefined regulating functions.Comment: 23 pages, epsfig.st

Continuous admission to primary school and mental health problems

Background: Younger children in a school class have higher rates of mental health problems if admission to primary school occurs once a year. This study examines whether this relative age effect also occurs if children are admitted to school continuously throughout the year. Methods: We assessed mental health problems based on parent-reports (using the Child Behavior Checklist, CBCL) and on professional assessments, among two Dutch national samples of in total 12,221 children aged 5-15 years (response rate: 86.9%). Results: At ages 5-6, we found a higher occurrence of mental health problems in relatively young children, both for mean CBCL scores (p = 0.017) and for problems assessed by child health professionals (p <0.0001). At ages 7-15, differences by relative age did not reach statistical significance. Conclusion: Continuous admission to primary school does not prevent mental health problems among young children, but may do so at older ages. Its potential for the prevention of mental problems deserves further study

Secondary traumatisation and emotional exhaustion in mental healthcare providers:The mediating role of social support

Background: Burnout, especially emotional exhaustion, is common among mental healthcare providers (MHP). It is caused by exposure to prolonged stress related job conditions, such as secondary traumatisation. Social support is a protective factor for developing emotional exhaustion. In addition, higher levels of social support are associated with lower levels of secondary traumatisation. However, it is unclear how social support and secondary traumatisation are related. Social support may be a protective factor for developing secondary traumatisation, as it is for emotional exhaustion. On the other hand, MHP who suffer more from secondary traumatisation might experience less social support, for example because they fear stigmatisation. This study examined whether social support mediates the relationship between secondary traumatisation and emotional exhaustion. Further, it is explored whether the relation between secondary traumatisation and social support is moderated by profession (physicians, psychologists and case managers). Method: In total, 593 MHP participated in this cross-sectional study. Participants completed a questionnaire including demographic characteristics, secondary traumatisation, emotional exhaustion, and social support. Results: It was shown that no MHP experience high levels of secondary traumatisation and relatively few experience high levels of emotional exhaustion, while they do experience much social support. Furthermore, as hypothesized, it was found that the relationship between secondary traumatisation and emotional exhaustion is partially mediated by social support. Finally, no moderation effect of profession was found. Conclusion: These results imply that MHP have access to social support and make use of it, preventing emotional exhaustion. Mental healthcare organisations should maintain these resources for social support to prevent emotional exhaustion. MHP who are less inclined to seek social support should receive extra attention, as should MHP who are more at risk of secondary traumatisation. Even though MHP experience the availability of social support, still 25% of the MHP do experience emotional exhaustion. Future research should examine which factors for this group contribute to the development of emotional exhaustion so that appropriate measures can be taken

Износ кругов из СТМ при зубошлифовании

The problems of increasing the efficiency of grinding highly precision gearwheels of the 3–4 degree of precision using superhard material tools are discussed. The efficiency of cubic boron nitride dish grinding wheels in various bonds has been studied. Recommendations how to use cubic boron nitride wheels in gear grinding are given

Gammaretrovirus-mediated correction of SCID-X1 is associated with skewed vector integration site distribution in vivo

We treated 10 children with X-linked SCID (SCID-X1) using gammaretrovirus-mediated gene transfer. Those with sufficient follow-up were found to have recovered substantial immunity in the absence of any serious adverse events up to 5 years after treatment. To determine the influence of vector integration on lymphoid reconstitution, we compared retroviral integration sites (RISs) from peripheral blood CD3(+) T lymphocytes of 5 patients taken between 9 and 30 months after transplantation with transduced CD34(+) progenitor cells derived from 1 further patient and I healthy donor. Integration occurred preferentially in gene regions on either side of transcription start sites, was clustered, and correlated with the expression level in CD34(+) progenitors during transduction. In contrast to those in CD34(+) cells, RISs recovered from engrafted CD3(+)T cells were significantly overrepresented within or near genes encoding proteins with kinase or transferase activity or involved in phosphorus metabolism. Although gross patterns of gene expression were unchanged in transduced cells, the divergence of RIS target frequency between transduced progenitor cells and post-thymic T lymphocytes indicates that vector integration influences cell survival, engraftment, or proliferation