Experiments and modeling of the chemo-mechanically coupled behavior of polymeric gels

Polymeric materials consist of mutually entangled or chemically crosslinked long njitmolecular chains which form a polymer network. Due to their molecular structure, the njitpolymeric materials are known to undergo large deformation in response to various njitenvironmental stimuli, such as temperature, chemical potential and light. When a polymer network is exposed to a suitable chemical solvent, the solvent molecules are able to diffuse inside the network, causing it to undergo a large volumetric deformation, known as swelling. In addition to volumetric deformation, this process involves the chemical mixing of the polymer network and solvent molecules, and is typically environmentally responsive. A polymeric material in this mixed and swollen state is known as a polymeric gel. Swollen polymers, or polymeric gels, find their application in the oil industry, soft robotics, drug delivery and microfluidic channels. Moreover, most of the organs inside our body are gel-like in structure, which makes this class of materials important for biomedical applications and tissue engineering. An important distinction between biological tissues and much of the previous literature on the mechanics of polymeric gels is that most biological tissues contain fibers. The existence of these fibers embedded in the material, causes the properties to be significantly different along the fiber direction. Recent years have seen the development of a vast number of large deformation continuum-level constitutive models aimed to capture the coupled diffusion-deformation behavior of polymeric gels. However, there is an insufficient amount of experimental data to complement such theoretical research. Thus, despite numerous potential applications, many aspects of polymeric gel behavior remain elusive. In addition, the diffusion-deformation behavior is known to be affected by the external stimuli. In the current state of the art there is a lack of theoretical models and robust simulation capabilities to account for the influence of such stimuli, hindering further advances in technologies involving polymeric gels. The purpose of this research is to bridge the gap between the experimental and theoretical studies, and provide reliable finite element simulation capabilities for polymeric gels. More specifically, the aim is to (i) experimentally characterize the behavior of polymeric gels, (ii) develop new experimentally motivated constitutive models and (iii) implement the models numerically for use in a finite element software. The final result of this research is a robust finite element method (FEM) code that can be used for simulations in the commercial software package Abaqus. Towards the goal, an experimental procedure is designed to thoroughly investigate the behavior of polymeric gels, and provide a direction for the development of novel constitutive models. The procedure involves mechanical testing of dry polymeric material, free swelling with suitable solvents, and mechanical testing when fully swollen. The experimental observations provide transformational insights in the mechanical behavior of polymeric gels, and are utilized to develop a continuum-level constitutive model. Further, the presence of embedded fibers in a swellable polymer matrix leads to anisotropy in the overall behavior. In order to capture this response, a constitutive model for fiber-reinforced polymeric gels is developed, that explicitly takes into account anisotropy in both the mechanical and diffusive behavior. The constitutive model is implemented as user element subroutine (UEL) in the commercial finite element software package Abaqus/Standard. Numerical simulations are performed to show the behavior of the model, and qualitative comparisons are made to experiments of a soft robotic gripper. In addition, many polymeric gels are known to respond or activate when exposed to a light stimulus. This light-driven alteration of the behavior is known to be caused by the photochemical reactions occurring inside the polymer network. Thus, the overall response of light-activated polymeric gels is affected by the mechanical stress, solvent content, and the extent of photochemical reaction caused by light irradiation. To account for such response of a polymeric gel, a continuum level constitutive model is developed and numerically implemented in Abaqus/Standard as a user element (UEL) subroutine

MAGIC and H.E.S.S. detect VHE gamma rays from the blazar OT081 for the first time: a deep multiwavelength study

https://pos.sissa.it/395/815/pdfPublished versio

Follow-up observations of GW170817 with the MAGIC telescopes

The discovery of the electromagnetic counterpart AT2017gfo and the GRB 170817A, associated to the binary neutron star merger GW170817, was one of the major advances in the study of gamma- ray bursts (GRBs) and the hallmark of the multi-messenger astronomy with gravitational waves. Another breakthrough in GRB physics is represented by the discovery of the highly energetic, teraelectronvolt (TeV) component in the GRB 190114C, possibly an universal component in all GRBs. This conclusion is also suggested by the hint of TeV emission in the short GRB 160821B and a few more events reported in the literature. The missing observational piece is the joint detection of TeV emission and gravitational waves from a short GRB and its progenitor. MAGIC observed the counterpart AT2017gfo as soon as the visibility conditions allowed it, namely from January to June 2018. These observations correspond to the maximum flux level observed in the radio and X-ray bands. The upper limits derived from TeV observations are compared with the modelling of the late non-thermal emission using the multi-frequency SED

Search for Gamma-ray Line emission from Dark Matter annihilation in the Galactic Centre with the MAGIC telescopes

We present the first search for dark matter (DM) spectral lines in the Galactic centre (GC) region with the MAGIC telescopes. The MAGIC telescopes, located on the Canary island of La Palma (Spain), are sensitive to gamma rays in the energy range from 50 GeV to 50 TeV. MAGIC has performed indirect DM searches in various astrophysical targets, such as dwarf spheroidal galaxies and clusters of galaxies. Observations at high zenith angles significantly increase the telescopes’ collection area and sensitivity for gamma rays in the TeV regime. We present the results obtained with more than 200 hours of high-zenith angle observations of the GC region with MAGIC, which allow us to probe promising heavy SUSY models, and to obtain competitive limits to the DM annihilation cross-section at high DM particle mass, compared to existing constraints. We will discuss how we exploit the data from a complex sky region to search for a line-like DM signature

Resolving the origin of very-high-energy gamma-ray emission from the PeVatron candidate SNR G106.3+2.7 using MAGIC telescopes

The supernova remnant (SNR) G106.3+2.7 associated with a 100 TeV gamma-ray source reported by HAWC, Tibet ASγ, and LHAASO Collaborations is one of the promising PeVatron candidates. Because the SNR contains an energetic pulsar wind nebula (PWN) dubbed Boomerang powered by the pulsar PSR J2229+6114, it is unclear whether the gamma-ray emission originates from the SNR or PWN complex and whether it is caused by hadronic or leptonic processes. We observed gamma rays above 200 GeV in the vicinity of the SNR G106.3+2.7 using the MAGIC telescopes for total ∼ 120 hours between May 2017 and August 2019 with an angular resolution of 0.07– 0.10 degrees, achieving an unprecedented exposure for this object at these energies. An extended gamma-ray emission spatially correlated with the radio continuum emission at the head and tail of SNR G106.3+2.7 was detected using the MAGIC telescopes. We found a significant gamma-ray emission above 5.65 TeV only from the SNR tail region, while no significant emission in the same band is found at the SNR head region containing the Boomerang PWN. Therefore, the gamma rays above 10 TeV detected with the air shower experiments are, likely, mainly emitted from the SNR tail region. In this presentation, we discuss the morphology of the gamma-ray emission from this complex region and attempt self-consistent multi-wavelength modeling of the energy spectrum

Upper limits on the very high energy emission from GRBs observed by MAGIC

The MAGIC collaboration has developed a dedicated observational strategy to repoint rapidly towards gamma-ray bursts (GRBs). In this contribution we present the information extracted from the large sample of the GRBs observed by MAGIC from 2013 to 2019. None of these GRBs were significantly detected, and this study aims to shed light on the reasons behind those non-detections. The same strategy had led to the successful detection of two GRBs at Very High Energies (VHE, E > 100 GeV). We describe the details of the MAGIC GRB observational procedure and the general properties of each observed GRB. The lack of detection can be attributed either to unfavourable conditions or GRB intrinsic properties, such as the magnetic field’s energy density, the bulk Lorentz factor, or the emitting region’s size. For the presented sample of GRBs, we show the methods used to obtain flux upper limits in the VHE range, and propose physical implications of the non-detection of VHE emission. These results constitute an essential reference point to study the broadband emission of GRBs, and for the Cherenkov telescope community to organize future follow-ups of GRBs at VHE energies

Multi-messenger characterization of Mrk501 during historically low X-ray and gamma-ray activity

Blazars, together with other active galactic nuclei, are the most luminous persistent sources in our universe; and therefore a prime candidate for very-high-energy (>0.2 TeV, VHE) gamma-ray observations. For the two MAGIC telescopes, the Mrk501 galaxy is among the brightest observed blazars due to its proximity. We report a multi-wavelength and multi-messenger study of Mrk501 with data from 2017 to 2020, when Mrk501 showed a VHE flux typically below 10% that of the Crab Nebula. During this time, we performed three long observations with NuSTAR, which characterized the hard X-ray emission during three different low-activity flux levels. This Mrk501 dataset provided the unprecedented opportunity to study multi-wavelength variability and correlations with sensitive instruments during historically low X-ray and VHE gamma-ray emission (below 5% of the Crab Nebula flux in the VHE range), which could be considered as the baseline emission of Mrk501. We complemented the broadband spectral energy distributions (SED) of the identified historically low X-ray and VHE gamma-ray flux with data published by IceCube, in order to evaluate the potential existence of a hadronic component that is stable (or slowly variable), and less visible than the leptonic component that may dominate the emission during typical and flaring activity. In this contribution, we will also describe the evolution of the broadband SED comparing different theoretical scenarios