Interpretation of the vibrational spectra of glassy polymers using coarse-grained simulations

The structure and vibrational density of states (VDOS) of polymer glasses are investigated using numerical simulations based on the classical Kremer-Grest bead-spring model. We focus on the roles of chain length and bending stiffness, the latter being set by imposing three-body angular potentials along chain backbones. Upon increasing the chain length and bending stiffness, structural reorganisation leads to volumetric expansion of the material and build-up of internal stresses. The VDOS has two dominant bands: a low frequency one corresponding to inter- and intra-chain non-bonding interactions and a high frequency one corresponding principally to vibrations of bonded beads that constitute skeletal chain backbones. Upon increasing the steepness of the angular potential, vibrational modes associated with chain bending gradually move from the low-frequency to the high-frequency band. This redistribution of modes is reflected in a reduction of the so-called Boson peak upon increasing chain stiffness. Remarkably, the finer structure and the peaks of the high-frequency band, and their variations with stiffness, can, for short chains, be explained using an analytical solution derived for a model triatomic molecule. For longer chains, the qualitative evolution of the VDOS with chain stiffness is similar, although the distinct peaks observed for short chains become increasingly smoothed-out. Our findings can be used to guide a systematic approach to interpretation of Brillouin and Raman scattering spectra of glassy polymers in future work, with applications in polymer processing diagnostics.Comment: To appear in Macromolecule

Parameter-free predictions of the viscoelastic response of glassy polymers from non-affine lattice dynamics

We study the viscoelastic response of amorphous polymers using theory and simulations. By accounting for internal stresses and considering instantaneous normal modes (INMs) within athermal non-affine theory, we make parameter-free predictions of the dynamic viscoelastic moduli obtained in coarse-grained simulations of polymer glasses at non-zero temperatures. The theoretical results show very good correspondence with rheology data collected from molecular dynamics simulations over five orders of magnitude in frequency, with some instabilities that accumulate in the low-frequency part on approach to the glass transition. These results provide evidence that the mechanical glass transition itself is continuous and thus represents a crossover rather than a true phase transition. The relatively sharp drop of the low-frequency storage modulus across the glass transition temperature can be explained mechanistically within the proposed theory: the proliferation of low-eigenfrequency vibrational excitations (boson peak and nearly-zero energy excitations) is directly responsible for the rapid growth of a negative non-affine contribution to the storage modulus.Comment: 10 pages, 7 figure

Monitoring urban heat island through google earth engine. Potentialities and difficulties in different cities of the United States

The aim of this work is to exploit the large-scale analysis capabilities of the innovative Google Earth Engine platform in order to investigate the temporal variations of the Urban Heat Island phenomenon as a whole. A intuitive methodology implementing a large-scale correlation analysis between the Land Surface Temperature and Land Cover alterations was thus developed. The results obtained for the Phoenix MA are promising and show how the urbanization heavily affects the magnitude of the UHI effects with significant increases in LST. The proposed methodology is therefore able to efficiently monitor the UHI phenomenon

Topology by dissipation

Topological states of fermionic matter can be induced by means of a suitably engineered dissipative dynamics. Dissipation then does not occur as a perturbation, but rather as the main resource for many-body dynamics, providing a targeted cooling into a topological phase starting from an arbitrary initial state. We explore the concept of topological order in this setting, developing and applying a general theoretical framework based on the system density matrix which replaces the wave function appropriate for the discussion of Hamiltonian ground-state physics. We identify key analogies and differences to the more conventional Hamiltonian scenario. Differences mainly arise from the fact that the properties of the spectrum and of the state of the system are not as tightly related as in a Hamiltonian context. We provide a symmetry-based topological classification of bulk steady states and identify the classes that are achievable by means of quasi-local dissipative processes driving into superfluid paired states. We also explore the fate of the bulk-edge correspondence in the dissipative setting, and demonstrate the emergence of Majorana edge modes. We illustrate our findings in one- and two-dimensional models that are experimentally realistic in the context of cold atoms.Comment: 61 pages, 8 figure

Comparative Language Learning Beliefs: Why Aptitude Matters

Language Learning Beliefs (LLB) are an important area for foreign and second language learning research that has grown considerably over the last decade, and which spans multi-disciplinary fields across education, linguistics and psychology (Martínez Agudo, 2014). These beliefs have become more important as they affect motivation and perhaps even language learning strategies (Zare-ee, 2010), though more research must be done in the latter area (Martínez Agudo, 2014). One understudied branch of LLB is that of language aptitude. Beliefs concerning language aptitude are not new, given that they appeared as a staple area of Horwitz’s seminal research for the BALLI questionnaire (Beliefs About Language Learning Inventory) (1987). However, beliefs on language aptitude need to be revisited given the multiple studies in social psychology on how beliefs affect learning when considering a given quality as innate or learned (Dweck, 2014). These studies show how believing intelligence to be fixed or incremental has a variety of consequences for learners that are fundamental for their long-term success in the classroom. Our aim in this paper is to merge these pertinent concepts to the foreign language classroom, in particular because the belief that intelligence is fixed or incremental mirrors the long-standing debate over language aptitude as innate or learned

A New Group of Two-Dimensional Non-van der Waals Materials with Ultra Low Exfoliation Energies

The exfoliation energy - quantifying the energy required to extract a two-dimensional (2D) sheet from the surface of a bulk material - is a key parameter determining the synthesizability of 2D compounds. Here, using ab initio calculations, we present a new group of non-van der Waals 2D materials derived from non-layered crystals which exhibit ultra low exfoliation energies. In particular for sulfides, surface relaxations are essential to correctly describe the associated energy gain needed to obtain reliable results. Taking into account long-range dispersive interactions has only a minor effect on the energetics and ultimately proves that the exfoliation energies are close to the ones of traditional van der Waals bound 2D compounds. The candidates with the lowest energies, 2D SbTlO$_3$ and MnNaCl$_3$, exhibit appealing electronic, potential topological, and magnetic features as evident from the calculated band structures making these systems an attractive platform for fundamental and applied nanoscience.Comment: 23 pages, 14 figure

Observations of microquasars with the MAGIC telescope

We report on the results from the observations in very high energy band (VHE, E_gamma > 100GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The observations were performed with the MAGIC telescope, for a total of 40 hours during 26 nights, spanning the period between June and November 2006. We report on the results of the searches for steady and variable gamma-ray signals, including the first experimental evidence for an intense flare, of duration between 1.5 and 24 hours.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of the MAGIC Collaboratio

Innovative PLF Tool to Assess Growing-Finishing Pigs’ Welfare

The main goal of the AWARTECH project (Animal Welfare Adjusted Real Time Envi ronmental Conditions of Housing) was to develop an innovative precision livestock tool that will support and reinforce the pig value chain, through the management of solutions based on monitoring, analysis and control of environmental, physiological, behaviour and animal performances parameters. Environmental data was collected by sensors of temperature, relative humidity, air velocity and gas concentration, which are integrated in an environmental control system (Webisense) and in a platform (Nidus). Webisense controlled the ventilation system, the cooling system and the heating system. The rectal and body surface temperatures were registered manual and automatically. In order to monitor the behaviour of the animals, video cameras were installed. An individual feeding machine equipped with a scale has been also installed. This equipment allow, through an RFID system, the individual monitoring and control of the amount of food supplied and ingested; the number and duration of visits; and the animal’s weight. The development of the AWARTECH platform resulted from the integration of data provided by Webisense, Nidus, feeding machine and video analytics as well as physiological data. This platform allows the control the environmental conditions based on welfare indicators promoting animal welfare