11,377 research outputs found
A simple physical model for scaling in protein-protein interaction networks
It has recently been demonstrated that many biological networks exhibit a
scale-free topology where the probability of observing a node with a certain
number of edges (k) follows a power law: i.e. p(k) ~ k^-g. This observation has
been reproduced by evolutionary models. Here we consider the network of
protein-protein interactions and demonstrate that two published independent
measurements of these interactions produce graphs that are only weakly
correlated with one another despite their strikingly similar topology. We then
propose a physical model based on the fundamental principle that (de)solvation
is a major physical factor in protein-protein interactions. This model
reproduces not only the scale-free nature of such graphs but also a number of
higher-order correlations in these networks. A key support of the model is
provided by the discovery of a significant correlation between number of
interactions made by a protein and the fraction of hydrophobic residues on its
surface. The model presented in this paper represents the first physical model
for experimentally determined protein-protein interactions that comprehensively
reproduces the topological features of interaction networks. These results have
profound implications for understanding not only protein-protein interactions
but also other types of scale-free networks.Comment: 50 pages, 17 figure
Short-term, medium-term and long-term effects of early parenting interventions in low- and middle-income countries: a systematic review
INTRODUCTION: Parenting interventions during early childhood are known to improve various child development outcomes immediately following programme implementation. However, less is known about whether these initial benefits are sustained over time. METHODS: We conducted a systematic literature review of parenting interventions in low- and middle-income countries (LMICs) that were delivered during the first 3 years of life and had completed a follow-up evaluation of the intervention cohort at least 1 year after the primary postintervention endpoint. We summarized intervention effects over time by child-level and parent-level outcomes as well as by timing of follow-up rounds in the short-term (1-3 years after programme completion), medium-term (4-9 years), and long-term (10+ years). We also conducted exploratory meta-analyses to compare effects on children's cognitive and behavioral development by these subgroups of follow-up rounds. RESULTS: We identified 24 articles reporting on seven randomised controlled trials of parenting interventions delivered during early childhood that had at least one follow-up study in seven LMICs. The majority of follow-up studies were in the short-term. Three trials conducted a medium-term follow-up evaluation, and only two trials conducted a long-term follow-up evaluation. Although trials consistently supported wide-ranging benefits on early child development outcomes immediately after programme completion, results revealed a general fading of effects on children's outcomes over time. Short-term effects were mixed, and medium-term and long-term effects were largely inconclusive. The exploratory meta-analysis on cognitive development found that pooled effects were significant at postintervention and in the short-term (albeit smaller in magnitude), but the effects were not significant in the medium-term and long-term. For behavioural development, the effects were consistently null over time. CONCLUSIONS: There have been few longer-term follow-up studies of early parenting interventions in LMICs. Greater investments in longitudinal intervention cohorts are needed in order to gain a more comprehensive understanding of the effectiveness of parenting interventions over the life course and to improve the design of future interventions so they can have greater potential for achieving and sustaining programme benefits over time
Laser Shock Microforming of Thin Metal Sheets
Continuous and long-pulse lasers have been used for the forming of metal sheets in macroscopic mechanical applications. However, for the manufacturing of micro-electromechanical systems (MEMS), the applicability of such type of lasers is limited by the long-relaxation-time of the thermal fields responsible for the forming phenomena. As a consequence of such slow relaxation, the final sheet deformation state is attained only after a certain time, what makes the generated internal residual stress fields more dependent on ambient conditions and might make difficult the subsequent assembly process from the point of view of residual stresses due to adjustment. The use of ns laser pulses provides a suitable parameter matching for the laser forming of an important range of sheet components used in MEMS that, preserving the short interaction time scale required for the predominantly mechanic (shock) induction of deformation residual stresses, allows for the successful processing of components in a medium range of miniaturization, particularly important according to its frequent use in such systems. In the present paper, a discussion is presented on the physics of laser shock microforming and the influence of the different effects on the net bending angle. The experimental setup used for the experiments, sample fabrication and experimental results of influence of number of laser pulses on the net bending angle are also presented
Quasiparticle Interference on the Surface of Topological Crystalline Insulator Pb(1-x)Sn(x)Se
Topological crystalline insulators represent a novel topological phase of
matter in which the surface states are protected by discrete point
group-symmetries of the underlying lattice. Rock-salt lead-tin-selenide alloy
is one possible realization of this phase which undergoes a topological phase
transition upon changing the lead content. We used scanning tunneling
microscopy (STM) and angle resolved photoemission spectroscopy (ARPES) to probe
the surface states on (001) PbSnSe in the topologically
non-trivial (x=0.23) and topologically trivial (x=0) phases. We observed
quasiparticle interference with STM on the surface of the topological
crystalline insulator and demonstrated that the measured interference can be
understood from ARPES studies and a simple band structure model. Furthermore,
our findings support the fact that PbSnSe and PbSe have
different topological nature.Comment: 5 pages, 4 figure
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