Fast radio bursts generated by coherent curvature radiation from compressed bunches for FRB 20190520B

The radiation mechanism of fast radio bursts (FRBs) has been extensively studied but still remains elusive. Coherent radiation is identified as a crucial component in the FRB mechanism, with charged bunches also playing a significant role under specific circumstances. In the present research, we propose a phenomenological model that draws upon the coherent curvature radiation framework and the magnetized neutron star, taking into account the kinetic energy losses of outflow particles due to inverse Compton scattering (ICS) induced by soft photons within the magnetosphere. By integrating the ICS deceleration mechanism for particles, we hypothesize a potential compression effect on the particle number density within a magnetic tube/family, which could facilitate achieving the necessary size for coherent radiation in the radial direction. This mechanism might potentially enable the dynamic formation of bunches capable of emitting coherent curvature radiation along the curved magnetic field. Moreover, we examine the formation of bunches from an energy perspective. Our discussion suggests that within the given parameter space the formation of bunches is feasible. Finally, we apply this model to FRB 20190520B, one of the most active repeating FRBs discovered and monitored by FAST. Several observed phenomena are explained, including basic characteristics, frequency downward drifting, and bright spots within certain dynamic spectral ranges.Comment: 16 pages, 9 figures, and 1 table. Accepted for publication in Ap

Investigation of the Acetylation Mechanism by GCN5 Histone Acetyltransferase

The histone acetylation of post-translational modification can be highly dynamic and play a crucial role in regulating cellular proliferation, survival, differentiation and motility. Of the enzymes that mediate post-translation modifications, the GCN5 of the histone acetyltransferase (HAT) proteins family that add acetyl groups to target lysine residues within histones, has been most extensively studied. According to the mechanism studies of GCN5 related proteins, two key processes, deprotonation and acetylation, must be involved. However, as a fundamental issue, the structure of hGCN5/AcCoA/pH3 remains elusive. Although biological experiments have proved that GCN5 mediates the acetylation process through the sequential mechanism pathway, a dynamic view of the catalytic process and the molecular basis for hGCN5/AcCoA/pH3 are still not available and none of theoretical studies has been reported to other related enzymes in HAT family. To explore the molecular basis for the catalytic mechanism, computational approaches including molecular modeling, molecular dynamic (MD) simulation and quantum mechanics/molecular mechanics (QM/MM) simulation were carried out. The initial hGCN5/AcCoA/pH3 complex structure was modeled and a reasonable snapshot was extracted from the trajectory of a 20 ns MD simulation, with considering post-MD analysis and reported experimental results. Those residues playing crucial roles in binding affinity and acetylation reaction were comprehensively investigated. It demonstrated Glu80 acted as the general base for deprotonation of Lys171 from H3. Furthermore, the two-dimensional QM/MM potential energy surface was employed to study the sequential pathway acetylation mechanism. Energy barriers of addition-elimination reaction in acetylation obtained from QM/MM calculation indicated the point of the intermediate ternary complex. Our study may provide insights into the detailed mechanism for acetylation reaction of GCN5, and has important implications for the discovery of regulators against GCN5 enzymes and related HAT family enzymes

Dynamic tuneable G protein-coupled receptor monomer-dimer populations

G protein-coupled receptors (GPCRs) are the largest class of membrane receptors, playing a key role in the regulation of processes as varied as neurotransmission and immune response. Evidence for GPCR oligomerisation has been accumulating that challenges the idea that GPCRs function solely as monomeric receptors; however, GPCR oligomerisation remains controversial primarily due to the difficulties in comparing evidence from very different types of structural and dynamic data. Using a combination of single-molecule and ensemble FRET, double electron–electron resonance spectroscopy, and simulations, we show that dimerisation of the GPCR neurotensin receptor 1 is regulated by receptor density and is dynamically tuneable over the physiological range. We propose a “rolling dimer” interface model in which multiple dimer conformations co-exist and interconvert. These findings unite previous seemingly conflicting observations, provide a compelling mechanism for regulating receptor signalling, and act as a guide for future physiological studies

Leading-effect vs. Risk-taking in Dynamic Tournaments: Evidence from a Real-life Randomized Experiment

Two 'order effects' may emerge in dynamic tournaments with information feedback. First, participants adjust effort across stages, which could advantage the leading participant who faces a larger 'effective prize' after an initial victory (leading-effect). Second, participants lagging behind may increase risk at the final stage as they have 'nothing to lose' (risk-taking). We use a randomized natural experiment in professional two-game soccer tournaments where the treatment (order of a stage-specific advantage) and team characteristics, e.g. ability, are independent. We develop an identification strategy to test for leading-effects controlling for risk-taking. We find no evidence of leading-effects and negligible risk-taking effects

Firm Level Allocative Inefficiency: Evidence from France

A large portion of productivity differentials among locations is related to density. Firms located in denser areas are more productive due to agglomeration economies (Combes et al., 2012). We provide in this paper an explanation of such economies: lower input misallocation. The distribution of resources among heterogeneous firms has relevant consequences on allocative efficiency and denser areas provide a more favorable environment for dynamic matching between employers and employees. Using a methodology proposed by Petrin and Sivadasan (2013) we are able to assess the degree of resource misallocation among firms within sectors for each of the 96 French "Départements". Based on firm-level productivity estimates, we identify in the gap between the value of the marginal product and marginal input price the output loss due to inefficiencies in inputs allocation. Over the period 1993-2007 the average gap at firm level is around 10 thousands euro, showing a relevant increase starting from the early 2000s. Importantly, firms misallocations are lower in denser areas, suggesting that the matching mechanism is playing a role in explaining the productivity premium of agglomerated locations

An examination of the keyboard technique of Bach, Haydn, Chopin, Scriabin and Prokofiev

Master's Project (M.Mu.) University of Alaska Fairbanks, 2016In this research paper, I will explore the keyboard technique of each composer presented in my recital: J.S. Bach, Franz Joseph Haydn, Frederic Chopin, Alexander Scriabin and Sergei Prokofiev. I hope to elucidate the physical approach used by each composer, and show in turn how that same approach influenced the music of each composer by analyzing the pieces performed in my recital. To understand the distinct technique of the composers, it is important to know some context. The instrument each composer wrote for necessarily influenced their technique and resulting composition. However, the instrument cannot explain every facet of technique, and it becomes necessary to understand the underlying aesthetics of technique. Moving chronologically from Bach to Prokofiev, a general trend of expansion in the use of the hand and arm will be seen throughout. Keyboards became louder and heavier in touch and the hand faced greater reaches in every generation. The technique of Bach and Haydn was largely focused on compact and relaxed hands with distinct finger movements, while Scriabin and Prokofiev at the other end require sweeping gestures that occupy the entire arm. However, it would be too easy to present this progression as a story that technique is only getting better and better, implying that the older composers were inferior to the later. That is simply false. Instead, extended study of each composer shows that many technical principles are universal. The baroque keyboardists were likely playing with more weight than popularly imagined and one cannot play Scriabin with mittens on the hands

Online Networks, Social Interaction and Segregation: An Evolutionary Approach

We have developed an evolutionary game model, where agents can choose between two forms of social participation: interaction via online social networks and interaction by exclusive means of face-to-face encounters. We illustrate the societal dynamics that the model predicts, in light of the empirical evidence provided by previous literature. We then assess their welfare implications. We show that dynamics, starting from a world in which online social interaction is less gratifying than offline encounters, will lead to the extinction of the sub-population of online networks users, thereby making Facebook and alike disappear in the long run. Furthermore, we show that the higher the propensity for discrimination between the two sub-populations of socially active individuals, the greater the probability that individuals will ultimately segregate themselves, making society fall into a social poverty trap

Structural insights into the cooperative remodeling of membranes by amphiphysin/BIN1

Amphiphysin2/BIN1 is a crescent-shaped N-BAR protein playing a key role in forming deeply invaginated tubes in muscle T-tubules. Amphiphysin2/BIN1 structurally stabilizes tubular formations in contrast to other N-BAR proteins involved in dynamic membrane scission processes; however, the molecular mechanism of the stabilizing effect is poorly understood. Using cryo-EM, we investigated the assembly of the amphiphysin/BIN1 on a membrane tube. We found that the N-BAR domains self-assemble on the membrane surface in a highly cooperative manner. Our biochemical assays and 3D reconstructions indicate that the N-terminal amphipathic helix Ho plays an important role in the initiation of the tube assembly and further in organizing BAR-mediated polymerization by locking adjacent N-BAR domains. Mutants that lack Ho or the tip portion, which is also involved in interactions of the neighboring BAR unit, lead to a disruption of the polymer organization, even though tubulation can still be observed. The regulatory region of amphiphysin/BIN1 including an SH3 domain does not have any apparent involvement in the polymer lattice. Our study indicates that the Ho helix and the BAR tip are necessary for efficient and organized self-assembly of amphiphysin/NBAR