What can we learn from "internal plateaus"? The peculiar afterglow of GRB 070110

Context: The origin of GRBs' prompt emission is highly debated. Proposed scenarios involve dissipation processes above or below the photosphere of an ultra-relativistic outflow. Aims: We search for observational features that would favour one scenario over the others by constraining the dissipation radius, the outflow magnetization or by indicating the presence of shocks. Bursts showing peculiarities can emphasize the role of a specific physical ingredient, which becomes more apparent under certain circumstances. Methods: We study GRB 070110, which exhibited several remarkable features during its early afterglow: a very flat plateau terminated by an extremely steep drop and immediately followed by a bump. We model the plateau as photospheric emission from a long lasting outflow of moderate Lorentz factor ($\Gamma\sim 20$) which lags behind an ultra-relativistic ($\Gamma> 100$) ejecta responsible for the prompt emission. We compute the dissipation of energy in the forward and reverse shocks resulting from this ejecta's deceleration by the external medium. Results: Photospheric emission from the long-lasting outflow can account for the plateau properties (luminosity and spectrum) assuming some dissipation takes place in the flow. The geometrical timescale at the photospheric radius is so short that the observed decline at the end of the plateau likely corresponds to the shut-down of the central engine. The following bump results from dissipated power in the reverse shock, which develops when the slower material catches up with the initially fast component, after it had been decelerated. Conclusions: Our interpretation suggests that the prompt phase resulted from dissipation above the photosphere while the plateau had a photospheric origin. If the bump is produced by the reverse shock, it implies an upper limit ($\sigma \lesssim 0.1$) on the magnetization of the slower material.Comment: 10 pages, 4 figures, accepted for publication in A&

Optimal ripple-free deadbeat controllers

A ripple-free deadbeat controller for a system exists if and only if there are no transmission zeros coinciding with the poles of the reference signal. Approaches to this problem often use the Diophantine equation solution. However, solutions provided by the Diophantine equation often exhibit extremely bad transient responses. This approach gives a new affine parametrization of solutions of the Diophantine equation. Based on this parametrization, LMI conditions are used to provide optimal or constrained controllers for design quantities such as overshoot, undershoot, control amplitude, 'slew rate' as well as for norm bounds such as l1, l2 and l infinity

The evolution of transcription-associated biases of mutations across vertebrates

<p>Abstract</p> <p>Background</p> <p>The interplay between transcription and mutational processes can lead to particular mutation patterns in transcribed regions of the genome. Transcription introduces several biases in mutational patterns; in particular it invokes strand specific mutations. In order to understand the forces that have shaped transcripts during evolution, one has to study mutation patterns associated with transcription across animals.</p> <p>Results</p> <p>Using multiple alignments of related species we estimated the regional single-nucleotide substitution patterns along genes in four vertebrate taxa: primates, rodents, laurasiatheria and bony fishes. Our analysis is focused on intronic and intergenic regions and reveals differences in the patterns of substitution asymmetries between mammals and fishes. In mammals, the levels of asymmetries are stronger for genes starting within CpG islands than in genes lacking this property. In contrast to all other species analyzed, we found a mutational pressure in dog and stickleback, promoting an increase of GC-contents in the proximity to transcriptional start sites.</p> <p>Conclusions</p> <p>We propose that the asymmetric patterns in transcribed regions are results of transcription associated mutagenic processes and transcription coupled repair, which both seem to evolve in a taxon related manner. We also discuss alternative mechanisms that can generate strand biases and involves error prone DNA polymerases and reverse transcription. A localized increase of the GC content near the transcription start site is a signature of biased gene conversion (BGC) that occurs during recombination and heteroduplex formation. Since dog and stickleback are known to be subject to rapid adaptations due to population bottlenecks and breeding, we further hypothesize that an increase in recombination rates near gene starts has been part of an adaptive process.</p

Flares in gamma-ray burst X-ray afterglows as prompt emission from slightly misaligned structured jets

We develop a model to explain the flaring activity in gamma-ray burst X-ray afterglows within the framework of slightly misaligned observers to structured jets. We suggest that flares could be the manifestation of prompt dissipation within the core of the jet, appearing to a misaligned observer in the X-ray band because of less favorable Doppler boosting. These flares appear during the afterglow phase because of core--observer light travel delays. In this picture, the prompt emission recorded by this observer comes from material along their line of sight, in the lateral structure of the jet, outside the jet's core. We start by laying down the basic analytical framework to determine the flares characteristics as a function of those of the gamma-ray pulse an aligned observer would have seen. We show that, for typical flare observing times and luminosities, there is indeed viable parameter space to explain flares in this way. We then analytically explore this model and show that it naturally produces flares with small width, a salient observed property of flares. We perform fits of our model to two Swift/XRT flares representing two different types of morphology, to show that our model can capture both. The ejection time of the core jet material responsible of the flare is a critical parameter. While it always remains small compared to the observed time of the flare, confirming that our model does not require very late central engine activity, late ejection times are strongly favored, sometimes larger than the observed duration of the parent gamma-ray burst's prompt phase as measured by $T_{90}$.Comment: Main text 11 pages, 4 figures and 2 tables. Submitted to MNRAS; comments welcom

INFLUENCE OF INVESTORS’ MONITORING ON EQUITY MUTUAL FUNDS’ PERFORMANCE

This paper analyzes the effect of investor monitoring on the performance of equity investment funds. For that purpose, we analyze the relationship between fund performance, measured using four-factor Alpha, and a set of control variables and monitoring proxy variables. We used monthly data for 1.317 funds, from January 2005 to April 2015. We organized the sample data into two subsamples, retail and institutional funds, to compare the performance of those funds whose clienteles presents, in principle, different monitoring capacities. Institutional funds presented superior performance compared to retail funds measured by net annual return as well as by four-factor Alpha. The variables investment, measured as the minimum initial investment requirement, and type of manager were statistically significant in the retail funds sample. The results show that greater capacity to monitor fund manager behavior could diminish the occurrence of activities against investor’s interests, which is one of the main contributions of this research

Antimicrobial and anti-inflammatory activity of chitosan-alginate nanoparticles: a targeted therapy for cutaneous pathogens.

Advances in nanotechnology have demonstrated potential application of nanoparticles (NPs) for effective and targeted drug delivery. Here we investigated the antimicrobial and immunological properties and the feasibility of using NPs to deliver antimicrobial agents to treat a cutaneous pathogen. NPs synthesized with chitosan and alginate demonstrated a direct antimicrobial activity in vitro against Propionibacterium acnes, the bacterium linked to the pathogenesis of acne. By electron microscopy (EM) imaging, chitosan-alginate NPs were found to induce the disruption of the P. acnes cell membrane, providing a mechanism for the bactericidal effect. The chitosan-alginate NPs also exhibited anti-inflammatory properties as they inhibited P. acnes-induced inflammatory cytokine production in human monocytes and keratinocytes. Furthermore, benzoyl peroxide (BP), a commonly used antiacne drug, was effectively encapsulated in the chitosan-alginate NPs and demonstrated superior antimicrobial activity against P. acnes compared with BP alone while demonstrating less toxicity to eukaryotic cells. Together, these data suggest the potential utility of topical delivery of chitosan-alginate NP-encapsulated drug therapy for the treatment of dermatologic conditions with infectious and inflammatory components

The Signature of Refreshed Shocks in the of Afterglow of GRB030329

GRB030329 displays one clear and, possibly, multiple less intense fast-rising ($\Delta t / t \sim 0.3$) jumps in its optical afterglow light curve. The decay rate of the optical light curve remains the same before and after the photon flux jumps. This may be the signature of energy injection into the forward and reverse shocked material at the front of the jet. In this study, we model the Gamma-Ray Burst (GRB) ejecta as a series of shells of material. We follow the dynamical evolution of the ejecta as it interacts with itself (i.e., internal shocks) and with the circumburst medium (i.e., external forward and reverse shocks), and we calculate the emission from each shock event assuming synchrotron emission. We confirm the viability of the model proposed by \citet{2003Natur.426..138G} in which the jumps in the optical afterglow light curve of GRB030329 are produced via refreshed shocks. The refreshed shocks may be the signatures of the collisions between earlier ejected material with an average Lorentz factor $\bar{\Gamma}\gtrsim 100$ and later ejected material with $\bar{\Gamma} \sim 10$ once the early material has decelerated due to interaction with the circumburst medium. We show that even if the late material is ejected with a spread of Lorentz factors, internal shocks naturally produce a narrow distribution of Lorentz factors ($\Delta\Gamma/\Gamma\lesssim0.1$), which is a necessary condition to produce the observed quick rise times of the jumps. These results imply a phase of internal shocks at some point in the dynamical evolution of the ejecta, which requires a low magnetization in the outflow.Comment: 11 pages, 6 figure