The Burst Cluster: Dark Matter in a Cluster Merger Associated with the Short Gamma Ray Burst, GRB 050509B

We have identified a merging galaxy cluster with evidence of two distinct sub-clusters. The X-ray and optical data suggest that the subclusters are moving away from each other after closest approach. This cluster merger was discovered from observations of the well localized short-duration gamma-ray burst (GRB), GRB 050509B. The Swift/Burst Alert Telescope (BAT) source position is coincident with a cluster of galaxies ZwCl 1234.0+02916. The subsequent Swift/X-Ray Telescope (XRT) localization of the X-ray afterglow found the GRB coincident with 2MASX J12361286+2858580, a giant red elliptical galaxy in the cluster. Deep multi-epoch optical images were obtained to constrain the evolution of the GRB afterglow, including a 27480s exposure in the F814W band with Hubble Space Telescope Advanced Camera for Surveys (ACS), among the deepest imaging ever obtained towards a known galaxy cluster in a single passband. We perform a weak gravitational lensing analysis, including mapping the total mass distribution of the merger system. Combined with Chandra X-ray Observatory and Swift/XRT observations, we investigate the dynamical state of the merger to probe the nature of the dark matter component. Our weak gravitational lensing measurements reveal a separation of the X-ray centroid of the western subcluster from the center of the mass and galaxy light distributions, similar to that of the famous "Bullet cluster". We conclude that the "Burst cluster" is another candidate merger system for determining the nature of dark matter and for studying the environment of short GRBs. We discuss connections between the cluster dynamical state and/or matter composition and compact object mergers, the leading model for the origin of short GRBs. Finally, we present results from a weak lensing survey based on archival Very Large Telescope (VLT) images in the areas of 5 other short GRBs.Comment: 17 pages, 7 figures, accepted by Ap

Flame retardancy of microcellular poly(lactic acid) foams prepared by supercritical CO2-assisted extrusion

Flame-retardant-treated cellulose (FR-cell) was used as bio-based charring agent in combination with ammonium polyphosphate (APP) based intumescent flame retardant (IFR) system to reduce the flammability of poly(lactic acid) (PLA) foams produced by supercritical carbon dioxide (sc-CO2) assisted extrusion. FR-cell was obtained by surface treatment of cellulose with diammonium phosphate (DAP) and boric acid (BA). To enhance foamability, the inherently low melt strength and slow crystallization rate of PLA was increased by adding epoxy-based chain extender (CE) and montmorillonite (MMT) nanoclay, respectively. The morphology of the foams was examined using water displacement method, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Thermal properties were assessed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Flammability was evaluated by limiting oxygen index (LOI) measurements, UL-94 tests and pyrolysis combustion flow calorimetry (PCFC). The continuous extrusion foaming technique allowed the preparation of low density PLA foams with uniform microcellular structure and void fractions higher than 90% accompanied with increased crystallinity of up to 19%. Despite the high expansion ratios (i.e. high surface area), the PLA foams showed excellent flame retardancy, UL-94 V-0 rate and LOI value of 31.5 vol% was achieved with an additive content as small as 19.5%. However, the flame retardant synergism evinced between IFR and MMT proved to be less pronounced in the expanded foams compared to bulk materials with identical additive contents

X-ray, lensing and Sunyaev Zel'dovich triaxial analysis of Abell 1835 out to R_{200}

Measuring the intrinsic shape and orientation of dark matter (DM) and intracluster (IC) gas in galaxy clusters is crucial to constraining their formation and evolution, and for enhancing the use of clusters as more precise cosmological probes. Extending our previous works, we present for the first time results from a triaxial joint analysis of the galaxy cluster Abell 1835, by means of X-ray, strong lensing (SL) and Sunyaev Zel'dovich (SZ) data. We parametrically reconstruct the full three-dimensional structure (triaxial shape and principal axis orientation) of both the DM and the IC gas, and the level of non-thermal pressure of the IC gas. We find that the intermediate-major and minor-major axis ratios of the DM are 0.71+/-0.08 and 0.59+/-0.05, respectively, and the major axis of the DM halo is inclined with respect to the line of sight at 18.3+/-5.2 deg. We present the first observational measurement of the non-thermal pressure out to R_{200}, which has been evaluated to be a few percent of the total energy budget in the internal regions, while reaching approximately 20% in the outer volumes. We discuss the implications of our method for the viability of the CDM scenario, focusing on the concentration parameter C and the inner slope of the DM gamma in order to test the cold dark matter (CDM) paradigm for structure formation: we measure gamma=1.01+/-0.06 and C=4.32+/-0.44, values which are close to the predictions of the CDM model. The combination of X-ray/SL data at high spatial resolution, capable of resolving the cluster core, with the SZ data, which are more sensitive to the cluster outer volume, allows us to characterize the level and the gradient of the gas entropy distribution and non-thermal pressure out to R_{200}, breaking the degeneracy among the physical models describing the thermal history of the ICM.Comment: MNRAS in press. arXiv admin note: substantial text overlap with arXiv:1108.076

Intumescent ethylene-vinyl acetate copolymer: Reaction to fire and mechanistic aspects

The concept of intumescence was applied to flame retard ethylene vinyl acetate copolymer (EVA). The paper examines two types of intumescence based on expandable graphite (EG, physical expansion) and on modified ammonium polyphosphate (AP760, chemical expansion). The incorporation of expandable graphite (EG) at relatively low loading (10 wt%) in EVA permits the reduction up to 65% of peak of heat release rate (pHRR) measured by cone calorimetry. The mode of action occurs via the formation of an expanded carbonaceous layer acting mainly as heat barrier limiting heat and mass transfer as evidenced by the temperature measurement as a function of time during cone calorimetry. The incorporation of small amount of ZnCO3 in EVA-AP760 enhances strongly the performance: pHRR was not reduced using the sole AP760 while it is decreased by 54% when only 2 wt% of AP760 is substituted by ZnCO3. A strong synergistic effect was therefore observed. Solid state NMR of 31P and 13C on cone residues prepared at different characteristic times evidenced the mechanism involved is the reinforcement of the protective char by the formation of phosphate glass limiting the creation of cracks and increasing the char strength

Maze running into intumescence: mechanistic aspects in polypropylene

International audienceThe concept of intumescence was applied to make flame retarded polypropylene (PP). This paper examines two types of intumescence in PP) based on expandable graphite (EG, physical expansion) and on modified ammonium polyphosphate (AP760, chemical expansion). Reaction to fire of PP containing EG and AP760 was first evaluated by cone calorimetry. The incorporation of intumescent additives at relatively low loading (10 wt%) in PP permits the reduction by 70% of pHRR. The mode of action occurs via the formation of an expandedcarbonaceous layer in all cases. The protective coating acts mainly as heat barrier in the case of the formulations containing AP760 or as heat dissipater with EG. The incorporation of small amount of EG in PP-AP760 modifies heat transfer in the coating creating a strong anisotropy. Upon expansion graphite worms align normal to the surface increasing the transverse heat conductivity (lower efficiency of the heat barrier) and hence, decreasing the fire performance (decrease by only 30% of pHRR). Kinetic analysis was then performed to quantify thethermal stability of the intumescent systems. It reveals that the intumescent additives do not modify the reactional scheme of the PP thermal decomposition but they increase slightly the thermal stability of the intumescent systems

2019 FIRE RETARDANCY ODYSSEY: A JOURNEY THROUGH THE MECHANISMS

Mechanisms of action are revisited through two case studies: (i) soot morphology released from EVA and EVA/ATH and (ii) anisotropy of heat gradient in intumescent PP

A pyrolysis model for the thermal decomposition of low-density polyethylene blended with ammonium polyphosphate and pentaerythritol

International audienceIn this work, a semi-empirical pyrolysis model is developed to predict the thermal decomposition behavior of an intumescent fire retardant (IFR) system consisting of ammonium polyphosphate/pentaerythritol (APP/PER) with the ratio 3:1 (wt/wt) in a low-density polyethylene (LDPE) matrix. This work is based on a previously developed semi-global reaction mechanism for the degradation of LDPE and APP/PER, which consists of two consecutive first-order reactions for the LDPE and five first and second-order reactions for the APP/PER combination. The apparent properties that define heat transport inside the pyrolyzing solid are determined via inverse modeling of cone calorimeter experiments for the pure LDPE and then for the complete IFR system. This is achieved by using the Shuffled Complex Evolution optimization algorithm. The flame heat flux in the cone calorimeter experiments is also evaluated by targeting the heat release rate (HRR) data in the optimization process of one of the cone radiative heat setups. The optimized parameters and flame heat feedback are in line with the literature and the robustness of the model is assessed by a comparison with the experimental data for a wide range of cone heat fluxes. Ignition times and peaks of HRR and total HRs are within the engineering accuracy whatever the flux conditions for both pure LDPE and the IFR system

A semi-global reaction mechanism for the thermal decomposition of low-density polyethylene blended with ammonium polyphosphate and pentaerythritol

International audienceA semi-global reaction mechanism has been developed to capture the decomposition of a polymer, i.e. low-density polyethylene (LDPE) that contains a condensed-phase-active intumescent flame retardant, i.e. ammonium polyphosphate (APP) mixed with pentaerythritol (PER) with ratio 3:1 (wt/wt). The methodology combines thermogravimetric analysis (TGA) in anaerobic environment over a wide range of heating rates and inverse modeling of these experiments based on the Shuffled Complex Evolution (SCE) optimization algorithm. The decomposition of neat LDPE can be described by a single first-order reaction. In contrast, the decomposition of the APP/PER additive is characterized by strong interactions between the reactants and a 5-step reaction mechanism was designed driven by the mechanisms of the intumescence process. The direct coupling of the 1-step reaction mechanism for LDPE and the 5-step reaction mechanism for APP/PER was found to provide decent predictions for the decomposition of the 90%LDPE/10% APP/PER blend. The slight interactions between the LDPE matrix and the APP/PER additive were taken into account by updating the kinetic parameters of two reactions, leading to a final robust and accurate 6-step reaction model

INTUMESCENT POLYOLEFINS: A JOURNEY FROM FIRE BEHAVIOR TO MECHANISTIC ASPECTS

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Metal-Organic Frameworks: New Fire Retardant for Polymeric Material

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