Degeneracy doubling and sublattice polarization in strain-induced pseudo-Landau levels

The degeneracy and spatial support of pseudo-Landau levels (pLLs) in strained honeycomb lattices systematically depends on the geometry -- for instance, in hexagonal and rectangular flakes the 0th pLL displays a twofold increased degeneracy, while the characteristic sublattice polarization of the 0th pLL is only fully realized in a zigzag-terminated triangle. These features are dictated by algebraic constraints in the atomistic theory, and signify a departure from the standard picture in which all qualitative differences between pLLs and Landau levels induced by a magnetic field trace back to the valley-antisymmetry of the pseudomagnetic field.Comment: 5 pages, 2 figure

Hybrid Glass Structures – Design Philosophy and Selected Checking Procedures

In this paper authors will summarise current design approaches for hybrid glass structures. Our past and present projects will be used to demonstrate how such structures can be justified using finite element analysis, analytical solutions in context of prescriptive national and international regulations, industry guidance’s developed and accumulated over past decades. General methods will be distilled, relevant for future hybrid glass structures

New algebraic relationships between tight binding models

In this thesis, we present a new perspective on tight binding models. Utilising the rich algebraic toolkit provided by a combination of graph and matrix theory allows us to explore tight binding systems related through polynomial relationships. By utilising ring operations of weighted digraphs through intermediate König digraph representations, we establish a polynomial algebra over finite and infinite periodic graphs, analogous to polynomial operations on adjacency matrices. Exploring the microscopic and macroscopic behaviour of polynomials in a graph-theoretic setting, we reveal elegant relationships between the symmetrical, topological, and spectral properties of a parent graph G and its family of child graphs p(G). Drawing a correspondence between graphs and tight binding models, we investigate deep-rooted connections between different quantum systems, providing a fresh angle from which to view established tight binding models. Finally, we visit topological chains, demonstrate how their properties relate to more trivial underlying chains through effective “square root” operations, and provide new insights into their spectral characteristics

“Crossing to the Other Side: The Afterworld and Aftermath of Trauma, War, and Exile in Rosa Chacel’s Ciencias naturales (1988)”

This article offers a reading of Rosa Chacel’s Ciencias naturales as a testimony to the trauma and grief that Republican supporters suffered as a result of the Nationalists’ victory in the Spanish Civil War, the consequences of exile, and the loss of the liberal Spain and cultural avant-garde with which Chacel identified. Whereas Chacel’s three diaries have attracted many critical studies, hardly any exist on Ciencias naturales and none, to my knowledge, has linked Chacel’s diaries with that novel. Arguing that Chacel’s use of the diary in Ciencias naturales can be seen as a site of memory as developed by Pierre Nora, this study draws on theories of trauma to illuminate how Chacel’s last work in her trilogy of memory novels bears witness to the original wound of the Civil War, constantly reiterating structures, symbols and motifs that articulate the paradigm of departure and return characteristic of traumatic memory. Finally, in its concluding section, the essay links Chacel’s Ciencias naturales with José Ortega y Gasset’s project of historical reason

Expanding the reaction scope of nucleic acids via metathesis

The sequence-specificity and programmability of DNA has led to an increasing emergence of DNA nanotechnology. However, with this comes a rise in the demand for DNA-compatible chemistries. This thesis explores the use metathesis, a carbon-carbon bond forming reaction, in DNA nanotechnology. Chapter 1 provides an introduction to DNA nanotechnology including DNA-origami, DNA-polymer conjugates and DNA-templated synthesis. The currently explored DNA-compatible chemistries are discussed, and the history and potential of the metathesis mechanism is covered. In Chapter 2 the compatibility of the metathesis reaction with DNA is explored. The stability of DNA in the presence of Ru-metathesis catalysts is assessed and any interactions between the catalyst and DNA are studied. Chapters 3 to 5 build upon the knowledge gained in Chapter 2 and focus on utilizing metathesis in DNA-nanotechnology. Chapter 3 covers attempts to prepare DNA bottlebrush polymers via the direct graft-through ring-opening metathesis polymerization of DNA macromonomers. Chapter 4 discusses attempts to isolate nucleic acid-functionalized metathesis catalysts with the aim of utilizing them in templating reactions. Finally, Chapter 5 covers an alternative in situ approach to DNA-functionalized metathesis catalysts which was explored following challenges with the isolation of catalysts discussed in Chapter 4

A negative regulatory function for the protein tyrosine phosphatase PTP2C revealed by reconstruction of platelet-derived growth factor receptor signalling in Schizosaccharomyces pombe

AbstractWe have exploited reconstitution in the fission yeast Schizosaccharomyces pombe to investigate how activation of phospholipase Cγ (PLCγ) by the platelet-derived growth factor-β receptor (PDGFβR) is regulated by the SH2 domain-containing protein tyrosine phosphatase PTP2C (also known as SHP-2). When co-expressed in S. pombe, PTP2C abolished PDGFβR autophosphorylation as well as its ability to phosphorylate and activate PLCγ. Inhibition of PDGFβR signalling by PTP2C appears specific insofar that PTP1C, a close homologue of PTP2C, does not suppress activation of either PDGFβR or PLCγ. Surprisingly, an inactive PTP2C mutant (C459S), which dephosphorylates neither PDGFβR nor PLCγ, remains fully effective as an inhibitor of [3H]inositol phosphate generation indicating that negative regulation is at least in part independent of catalytic activity. This contrasts with PLCγ activation by c-Src which, although blocked by active PTP2C, is not inhibited by the mutant PTP2C C459S. These observations indicate that in addition to a reported positive role relaying trophic signals, PTP2C can also exert a negative effect on the PDGFβR and its signalling to PLCγ

Topological tight-binding models from nontrivial square roots

We describe a versatile mechanism that provides tight-binding models with an enriched, topologically nontrivial band structure. The mechanism is algebraic in nature, and leads to tight-binding models that can be interpreted as a nontrivial square root of a parent lattice Hamiltonian—in analogy to the passage from a Klein-Gordon equation to a Dirac equation. In the tight-binding setting, the square-root operation admits to induce spectral symmetries at the expense of broken crystal symmetries. As we illustrate in detail for a simple one-dimensional example, the emergent and inherited spectral symmetries equip the energy gaps with independent topological quantum numbers that control the formation of topologically protected states. We also describe an implementation of this system in silicon photonic structures, outline applications in higher dimensions, and provide a general argument for the origin and nature of the emergent symmetries, which are typically nonsymmorphic

Universal sign control of coupling in tight-binding lattices

We present a method of locally inverting the sign of the coupling term in tight-binding systems, by means of inserting a judiciously designed ancillary site and eigenmode matching of the resulting vertex triplet. Our technique can be universally applied to all lattice configurations, as long as the individual sites can be detuned. We experimentally verify this method in laser-written photonic lattices and confirm both the magnitude and the sign of the coupling by interferometric measurements. Based on these findings, we demonstrate how such universal sign-flipped coupling links can be embedded into extended lattice structures to impose a Z2-gauge transformation. This opens a new avenue for investigations on topological effects arising from magnetic fields with aperiodic flux patterns or in disordered systems

Subclinical infection without encephalitis in mice following intranasal exposure to Nipah virus-Malaysia and Nipah virus-Bangladesh

BACKGROUND: Nipah virus and Hendra virus are closely related and following natural or experimental exposure induce similar clinical disease. In humans, encephalitis is the most serious outcome of infection and, hitherto, research into the pathogenesis of henipavirus encephalitis has been limited by the lack of a suitable model. Recently we reported a wild-type mouse model of Hendra virus (HeV) encephalitis that should facilitate detailed investigations of its neuropathogenesis, including mechanisms of disease recrudescence. In this study we investigated the possibility of developing a similar model of Nipah virus encephalitis. FINDINGS: Aged and young adult wild type mice did not develop clinical disease including encephalitis following intranasal exposure to either the Malaysia (NiV-MY) or Bangladesh (NiV-BD) strains of Nipah virus. However viral RNA was detected in lung tissue of mice at euthanasia (21 days following exposure) accompanied by a non-neutralizing antibody response. In a subsequent time course trial this viral RNA was shown to be reflective of an earlier self-limiting and subclinical lower respiratory tract infection through successful virus re-isolation and antigen detection in lung. There was no evidence for viremia or infection of other organs, including brain. CONCLUSIONS: Mice develop a subclinical self-limiting lower respiratory tract infection but not encephalitis following intranasal exposure to NiV-BD or NiV-MY. These results contrast with those reported for HeV under similar exposure conditions in mice, demonstrating a significant biological difference in host clinical response to exposure with these viruses. This finding provides a new platform from which to explore the viral and/or host factors that determine the neuroinvasive ability of henipaviruses