541 research outputs found
The self-assembly and evolution of homomeric protein complexes
We introduce a simple "patchy particle" model to study the thermodynamics and
dynamics of self-assembly of homomeric protein complexes. Our calculations
allow us to rationalize recent results for dihedral complexes. Namely, why
evolution of such complexes naturally takes the system into a region of
interaction space where (i) the evolutionarily newer interactions are weaker,
(ii) subcomplexes involving the stronger interactions are observed to be
thermodynamically stable on destabilization of the protein-protein interactions
and (iii) the self-assembly dynamics are hierarchical with these same
subcomplexes acting as kinetic intermediates.Comment: 4 pages, 4 figure
Splaying Preorders and Postorders
Let be a binary search tree. We prove two results about the behavior of
the Splay algorithm (Sleator and Tarjan 1985). Our first result is that
inserting keys into an empty binary search tree via splaying in the order of
either 's preorder or 's postorder takes linear time. Our proof uses the
fact that preorders and postorders are pattern-avoiding: i.e. they contain no
subsequences that are order-isomorphic to and ,
respectively. Pattern-avoidance implies certain constraints on the manner in
which items are inserted. We exploit this structure with a simple potential
function that counts inserted nodes lying on access paths to uninserted nodes.
Our methods can likely be extended to permutations that avoid more general
patterns. Second, if is any other binary search tree with the same keys as
and is weight-balanced (Nievergelt and Reingold 1973), then splaying
's preorder sequence or 's postorder sequence starting from takes
linear time. To prove this, we demonstrate that preorders and postorders of
balanced search trees do not contain many large "jumps" in symmetric order, and
exploit this fact by using the dynamic finger theorem (Cole et al. 2000). Both
of our results provide further evidence in favor of the elusive "dynamic
optimality conjecture.
Continuum elastic modeling of graphene resonators
Starting from an atomistic approach we have derived a hierarchy of
successively more simplified continuum elasticity descriptions for modeling the
mechanical properties of suspended graphene sheets. The descriptions are
validated by applying them to square graphene-based resonators with clamped
edges and studying numerically their mechanical responses. Both static and
dynamic responses are treated. We find that already for deflections of the
order of 0.5{\AA} a theory that correctly accounts for nonlinearities is
necessary and that for many purposes a set of coupled Duffing-type equations
may be used to accurately describe the dynamics of graphene membranes.Comment: 7 pages, 5 figure
LOFAR discovery of a double radio halo system in Abell 1758 and radio/X-ray study of the cluster pair
Radio halos and radio relics are diffuse synchrotron sources that extend over Mpc-scales and are found in a number of merger galaxy clusters. They are believed to form as a consequence of the energy that is dissipated by turbulence and shocks in the intra-cluster medium (ICM). However, the precise physical processes that generate these steep synchrotron spectrum sources are still poorly constrained. We present a new LOFAR observation of the double galaxy cluster Abell 1758. This system is composed of A1758N, a massive cluster hosting a known giant radio halo, and A1758S, which is a less massive cluster whose diffuse radio emission is confirmed here for the first time. Our observations have revealed a radio halo and a candidate radio relic in A1758S, and a suggestion of emission along the bridge connecting the two systems which deserves confirmation. We combined the LOFAR data with archival VLA and GMRT observations to constrain the spectral properties of the diffuse emission. We also analyzed a deep archival Chandra observation and used this to provide evidence that A1758N and A1758S are in a pre-merger phase. The ICM temperature across the bridge that connects the two systems shows a jump which might indicate the presence of a transversal shock generated in the initial stage of the merger
Radio observations of the merging galaxy cluster system Abell 3391-Abell 3395
The pre-merging system of galaxy clusters Abell 3391-Abell 3395 located at a
mean redshift of 0.053 has been observed at 1 GHz in an ASKAP/EMU Early Science
observation as well as in X-rays with eROSITA. The projected separation of the
X-ray peaks of the two clusters is 50 or 3.1 Mpc. Here we
present an inventory of interesting radio sources in this field around this
cluster merger. While the eROSITA observations provide clear indications of a
bridge of thermal gas between the clusters, neither ASKAP nor MWA observations
show any diffuse radio emission coinciding with the X-ray bridge. We derive an
upper limit on the radio emissivity in the bridge region of . A non-detection of diffuse radio emission in the X-ray bridge between
these two clusters has implications for particle-acceleration mechanisms in
cosmological large-scale structure. We also report extended or otherwise
noteworthy radio sources in the 30 deg field around Abell 3391-Abell 3395.
We identified 20 Giant Radio Galaxies, plus 7 candidates, with linear projected
sizes greater than 1 Mpc. The sky density of field radio galaxies with largest
linear sizes of Mpc is deg, three times higher than
previously reported. We find no evidence for a cosmological evolution of the
population of Giant Radio Galaxies. Moreover, we find seven candidates for
cluster radio relics and radio halos.Comment: Astronomy & Astrophysics, in pres
Reciprocity as a foundation of financial economics
This paper argues that the subsistence of the fundamental theorem of contemporary financial mathematics is the ethical concept ‘reciprocity’. The argument is based on identifying an equivalence between the contemporary, and ostensibly ‘value neutral’, Fundamental Theory of Asset Pricing with theories of mathematical probability that emerged in the seventeenth century in the context of the ethical assessment of commercial contracts in a framework of Aristotelian ethics. This observation, the main claim of the paper, is justified on the basis of results from the Ultimatum Game and is analysed within a framework of Pragmatic philosophy. The analysis leads to the explanatory hypothesis that markets are centres of communicative action with reciprocity as a rule of discourse. The purpose of the paper is to reorientate financial economics to emphasise the objectives of cooperation and social cohesion and to this end, we offer specific policy advice
The spatial contours of wellbeing: A content analysis of metaphor in academic discourse
In thinking and talking about wellbeing, people often deploy spatial metaphors, such as identifying positive and negative affect with ‘up’ and ‘down’ respectively. However, there has not yet been a systematic investigation of how wellbeing is represented through metaphor. To shed light on this topic, a content analysis was conducted of spatial metaphors in academic discourse on wellbeing, focusing on recent editions of two leading journals, the Journal of Positive Psychology, and the British Journal of Clinical Psychology. Across 28 papers, 54 spatial metaphors were identified, grouped into four main categories: verticality; horizontality; configuration; and dynamism. Above all, wellbeing is associated with interior expansiveness, with positive valence usually attaching to vertical metaphors of height and depth, horizontal metaphors of width and breadth, and configuration metaphors of size and growth. The analysis thus offers valuable insights into the subjective dynamics of wellbeing
TRH: Pathophysiologic and clinical implications
Thyrotropin releasing hormone is thought to be a tonic stimulator of the pituitary TSH secretion regulating the setpoint of the thyrotrophs to the suppressive effect of thyroid hormones. The peptide stimulates the release of normal and elevated prolactin. ACTH and GH may increase in response to exogenous TRH in pituitary ACTH and GH hypersecretion syndromes and in some extrapituitary diseases.
The pathophysiological implications of extrahypothalamic TRH in humans are essentially unknown.
The TSH response to TRH is nowadays widely used as a diganostic amplifier in thyroid diseases being suppressed in borderline and overt hyperthyroid states and increased in primary thyroid failure. In hypothyroid states of hypothalamic origin, TSH increases in response to exogenous TRH often with a delayed and/or exaggerated time course.
But in patients with pituitary tumors and suprasellar extension TSH may also respond to TRH despite secondary hypothyroidism. This TSH increase may indicate a suprasellar cause for the secondary hypothyroidism, probably due to portal vessel occlusion. The TSH released in these cases is shown to be biologically inactive
Prediction of fatal or near-fatal cardiac arrhythmia events in patients with depressed left ventricular function after an acute myocardial infarction†
To determine whether risk stratification tests can predict serious arrhythmic events after acute myocardial infarction (AMI) in patients with reduced left ventricular ejection fraction (LVEF <= 0.40). A total of 5869 consecutive patients were screened in 10 European centres, and 312 patients (age 65 +/- 11 years) with a mean LVEF of 31 +/- 6% were included in the study. Heart rate variability/turbulence, ambient arrhythmias, signal-averaged electrocardiogram (SAECG), T-wave alternans, and programmed electrical stimulation (PES) were performed 6 weeks after AMI. The primary endpoint was ECG-documented ventricular fibrillation or symptomatic sustained ventricular tachycardia (VT). To document these arrhythmic events, the patients received an implantable ECG loop-recorder. There were 25 primary endpoints (8.0%) during the follow-up of 2 years. The strongest predictors of primary endpoint were measures of heart rate variability, e.g. hazard ratio (HR) for reduced very-low frequency component ( <5.7 ln ms(2)) adjusted for clinical variables was 7.0 (95% CI: 2.4-20.3, P <0.001). Induction of sustained monomorphic VT during PES (adjusted HR = 4.8, 95% CI, 1.7-13.4, P = 0.003) also predicted the primary endpoint. Fatal or near-fatal arrhythmias can be predicted by many risk stratification methods, especially by heart rate variability, in patients with reduced LVEF after AM
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