A Tight Binding Approach to Strain and Curvature in Monolayer Transition-Metal Dichalcogenides

We present a model of the electronic properties of monolayer transition-metal dichalcogenides based on a tight binding approach which includes the effects of strain and curvature of the crystal lattice. Mechanical deformations of the lattice offer a powerful route for tuning the electronic structure of the transition-metal dichalcogenides, as changes to bond lengths lead directly to corrections in the electronic Hamiltonian while curvature of the crystal lattice mixes the orbital structure of the electronic Bloch bands. We first present an effective low energy Hamiltonian describing the electronic properties near the K point in the Brillouin zone, then present the corrections to this Hamiltonian due to arbitrary mechanical deformations and curvature in a way which treats both effects on an equal footing. This analysis finds that local area variations of the lattice allow for tuning of the band gap and effective masses, while the application of uniaxial strain decreases the magnitude of the direct band gap at the K point. Additionally, strain induced bond length modifications create a fictitious gauge field with a coupling strength that is smaller than that seen in related materials like graphene. We also find that curvature of the lattice leads to the appearance of both an effective in-plane magnetic field which couples to spin degrees of freedom and a Rashba-like spin-orbit coupling due to broken mirror inversion symmetry.Comment: 16 pages, 2 figures, revised version v

A framework for P2P application development

Although Peer-to-Peer (P2P) computing has become increasingly popular over recent years, there still exist only a very small number of application domains that have exploited it on a large scale. This can be attributed to a number of reasons including the rapid evolution of P2P technologies, coupled with their often-complex nature. This paper describes an implemented abstraction framework that seeks to aid developers in building P2P applications. A selection of example P2P applications that have been developed using this framework are also presented

Ultrasound Use and “Overuse”

The U.S. Department of Health and Human Services Office of the Inspector General has issued a report concerning “high use” and “questionable use” ultrasound. Findings include those geographic areas where occurrences are most frequent, as well as the most common elements that characterize questionable use. While not its primary focus, emergency physician performed bedside ultrasound is within the scope of the report. Implications for emergency ultrasound are discussed and practice recommendations made for minimizing regulatory exposure for emergency physicians and departments

Supporting the active learning of collaborative database browsing techniques

We describe the implications of a study of database browsing behaviour for the development of a system to support more effective browsing. In particular we consider the importance of collaborative working, both in learning browsing skills and in co‐operating on a shared information‐retrieval task. From our study, we believe that an interface to support collaboration should promote the awareness of the activities of others, better visualization of the information data structures being browsed, and effective communication of the browsing process

Manipulating type-I and type-II Dirac polaritons in cavity-embedded honeycomb metasurfaces

Pseudorelativistic Dirac quasiparticles have emerged in a plethora of artificial graphene systems that mimic the underlying honeycomb symmetry of graphene. However, it is notoriously difficult to manipulate their properties without modifying the lattice structure. Here we theoretically investigate polaritons supported by honeycomb metasurfaces and, despite the trivial nature of the resonant elements, we unveil rich Dirac physics stemming from a non-trivial winding in the light-matter interaction. The metasurfaces simultaneously exhibit two distinct species of massless Dirac polaritons, namely type-I and type-II. By modifying only the photonic environment via an enclosing cavity, one can manipulate the location of the type-II Dirac points, leading to qualitatively different polariton phases. This enables one to alter the fundamental properties of the emergent Dirac polaritons while preserving the lattice structure - a unique scenario which has no analog in real or artificial graphene systems. Exploiting the photonic environment will thus give rise to unexplored Dirac physics at the subwavelength scale

Fun by design: The game design activity and its iterative process as (playful) learning practices

THIS CONTRIBUTION PROPOSES A CRITICAL REVIEW OF THE RESULTS OF A WORKSHOP HELD AT POLITECNICO DI MILANO PROBLEMATISING HOW PLAYFULNESS AND ‘FUN BY DESIGN’ AFFECT GAME DESIGN ACTIVITIES AND CONTRIBUTE TO GIVING STUDENTS A DIFFERENT AWARENESS OF THE PLAY EXPERIENCE. THE PRESENTED ACTIVITIES ARE PART OF THE AUTHORS’ JOINT RESEARCH IN THE DOMAIN OF SITUATED GAMING AS A FORM OF PLAYFUL LEARNING IN HIGHER EDUCATION, WHICH INVESTIGATES THE PART OF BOTH THE DESIGNERS AND THE PLAYERS (ACKERMANN & MARIANI, 2015). THE ANALYSIS INVESTIGATES HOW THE ITERATIVE DESIGN PROCESS SIMULTANEOUSLY ELICITS FUN AND ACTIVATES REFLECTIONS ON THE GAME DESIGN PRACTICE AND THE PLAYTESTING ACTIVITY AS A NODAL MOMENT FOR PLAYERS AND DESIGNERS, WHERE SERIOUSNESS AND PLAYFULNESS INTERSECT. ALLOWING AND REQUIRING PLAYFUL PARTICIPATION ON MULTIPLE LEVELS, AND AIMING TO EMPHASISE THE PLAYERS’ PERSPECTIVES, WE ASKED 45 STUDENTS TO (1) DESIGN LOCATION BASED MOBILE GAMES, (2) PERFORM THE OBSERVATION/ VERIFICATION PROCESS AND (3) EXPLORE ITS ELUSIVE AND CHALLENGING PHASES. DATA WAS COLLECTED FROM RAPID ETHNOGRAPHIES AND QUESTIONNAIRES COMPILED IN THE PROCESS. THE CONTRIBUTION EXPANDS THE REASONING FROM THE FUNDAMENTAL DISCOURSE OF MEANINGS EMBEDDED AND COMMUNICATED THROUGH GAMES, TO THE IMPORTANCE OF THE GAME DESIGN ACTIVITY AS A RECURSIVE PROCESS OF KNOWLEDGE ACQUISITION AND AS A SPECIFIC FORM OF PLAYFUL LEARNING

Signatures of spin in the n=1/3 Fractional Quantum Hall Effect

The activation gap Delta of the fractional quantum Hall state at constant filling n =1/3 is measured in wide range of perpendicular magnetic field B. Despite the full spin polarization of the incompressible ground state, we observe a sharp crossover between a low-field linear dependence of Delta on B associated to spin texture excitations and a Coulomb-like behavior at large B. From the global gap-reduction we get information about the mobility edges in the fractional quantum Hall regime.Comment: 4 pages, 3 figure