Integrability in the chiral model of magic angles

Magic angles in the chiral model of twisted bilayer graphene are parameters for which the chiral version of the Bistritzer--MacDonald Hamiltonian exhibits a flat band at energy zero. We compute the sums over powers of (complex) magic angles and use that to show that the set of magic angles is infinite. We also provide a new proof of the existence of the first real magic angle, showing also that the corresponding flat band has minimal multiplicity for the simplest possible choice of potentials satisfying all symmetries. These results indicate (though not prove) a hidden integrability of the chiral model

“It May Be a Pain in the Backside but...” Insights into the Resilience of Business after GDPR

The General Data Protection Regulation (GDPR) came into effect in May 2018 and is designed to safeguard European Union (EU) citizens’ data privacy. The benefits of the regulation to consumers’ rights and to regulators’ powers are well known. The benefits to regulated businesses are less obvious and under-researched. We conduct exploratory research into understanding the sociotechnical impacts and resilience of business in the face of a major new disruptive regulation. In particular, we investigate if GDPR is all pain and no gain. Using semi-structured interviews, we survey 14 senior-level executives responsible for business, finance, marketing, compliance and technology drawn from six companies in the UK and Ireland. We find the threat of fines has focused the corporate mind and made business more privacy aware. Organisationally, it has created new power bases within companies to advocate GDPR. It has forced companies to modernise their platforms and indirectly benefited them with better risk management processes, information security infrastructure and up to date customer databases. Compliance, for some, is used as a reputational signal of trustworthiness. Many implementation challenges remain. New business development and intra-company communication is more constrained. Regulation has increased costs and internal bureaucracy. Grey areas remain due to a lack of case law. Disgruntled customers and ex-employees weaponise Subject Access Requests (SAR) as a tool of retaliation. All small and medium-sized businesses in our sample see GDPR as overkill and overwhelming. We conclude GDPR may be regarded as a pain by business but it has made it more careful with data. It created a short-term disruption that monopolised IT budgets in the run-up to GDPR and created a long-term disruption to company politics as Compliance and Information Security leverage the regulation for budget and control. The rising trend in the number of fines issued by national data protection regulators and the establishment of new case law will continue to reshape organisations

Fine structure of flat bands in a chiral model of magic angles

We analyze symmetries of Bloch eigenfunctions at magic angles for the Tarnopolsky--Kruchkov--Vishwanath chiral model of the twisted bilayer graphene (TBG) following the framework introduced by Becker--Embree--Wittsten--Zworski. In particular, we show that vanishing of the first Bloch eigenvalue away from the Dirac points implies its vanishing at all momenta, that is the existence of a flat band. We then study how the multiplicity of the flat band is related to the nodal set of the Bloch eigenfunctions. We also demonstrate that for a generic choice of tunneling potentials, obeying all translational and rotational symmetries, the Hamiltonian only exhibits flat bands of minimal multiplicity. We conclude with two numerical observations about the structure of flat bands

Degenerate flat bands in twisted bilayer graphene

We prove that in the chiral limit of the Bistritzer-MacDonald Hamiltonian, there exist magic angles at which the Hamiltonian exhibits flat bands of multiplicity four instead of two. We analyze the structure of the Bloch functions associated with the four bands, the corresponding Chern number, and show that there exist infinitely many degenerate magic angles for a generic choice of tunnelling potentials.Comment: New results on the existence of non-real magic angle

Chiral limit of twisted trilayer graphene

We initiate the mathematical study of the Bistritzer-MacDonald Hamiltonian for twisted trilayer graphene in the chiral limit (and beyond). We develop a spectral theoretic approach to investigate the presence of flat bands under specific magic parameters. This allows us to derive trace formulae that show that the tunnelling parameters that lead to flat bands are nowhere continuous as functions of the twisting angles

Infective endocarditis caused by Pseudomonas stutzeri in a patient with Marfan syndrome: Case report and brief literature review

Invasive infections due to Pseudomonas stutzeri have rarely been described and mainly occur in immunocompromised individuals. We report a case of infective endocarditis caused by P. stutzeri after previous cardiac surgery in a Lebanese patient with Marfan syndrome. We review the literature and conclude that this pathogen may be of particular medical relevance in the Mediterranean Basin

Late-onset native valve endocarditis caused by Corynebacterium kroppenstedtii

Corynebacterium kroppenstedtii is an emerging cause of granulomatous mastitis and recurrent breast abscesses in women, but data on its clinical relevance in nongynecological disease conditions are limited. Here, we report the first case of a late-onset endocarditis of a native aortic valve in a 73-year-old male patient who presented with symptomatic aortic insufficiency. Echocardiography and cardiac computed tomography revealed the perforation of the noncoronary cusp and a large perivalvular abscess cavity. Hence, the surgical replacement of the aortic valve and aortic root were performed. Intraoperatively obtained tissue specimens grew C. kroppenstedtii and the patient made a full recovery after a 6-week course of antibiotic treatment. We briefly review the literature pertaining to antimicrobial susceptibility patterns of C. kroppenstedtii and available treatment recommendations. Our report calls for further studies to assess the role of this bacterium as a causative agent of infections other than granulomatous mastitis

The role of supply chains for the sustainability transformation of global food systems: A large‐scale, systematic review of food cold chains

Global food systems need an urgent transformation to be compatible with sustainable development. While much of the recent academic discussion has focused on food production and consumption, food supply chains have received considerably less attention. Here, we conduct a large-scale, systematic literature review of 48,014 academic articles to assess the links between the food cold chain literature and sustainable development. We find a multitude of deep links between food cooling and the Sustainable Development Goals (SDGs), but also identify underexplored areas of sustainable food cooling research regarding its (1) goals, (2) analytical depth, and (3) context specificity: There is a limited understanding how several relevant synergies between SDGs can be captured, how to best design sustainable food cold chains across multiple value chain stages, and how to scale sustainable cold chains in low-income and lower-middle-income country contexts. We recommend to explicitly consider the salient interconnections between SDGs, increase the analytical depth by deploying more system-level approaches across entire value chains, and focus on localized solutions in contexts where food supply chains are most underdeveloped

Storms and the Depletion of Ammonia in Jupiter: I. Microphysics of “Mushballs”

Microwave observations by the Juno spacecraft have shown that, contrary to expectations, the concentration of ammonia is still variable down to pressures of tens of bars in Jupiter. We show that during strong storms able to loft water ice into a region located at pressures between 1.1 and 1.5 bar and temperatures between 173 and 188 K, ammonia vapor can dissolve into water ice to form a low‐temperature liquid phase containing about one‐third ammonia and two‐third water. We estimate that, following the process creating hailstorms on Earth, this liquid phase enhances the growth of hail‐like particles that we call mushballs. We develop a simple model to estimate the growth of these mushballs, their fall into Jupiter’s deep atmosphere, and their evaporation. We show that they evaporate deeper than the expected water cloud base level, between 5 and 27 bar depending on the assumed abundance of water ice lofted by thunderstorms and on the assumed ventilation coefficient governing heat transport between the atmosphere and the mushball. Because the ammonia is located mostly in the core of the mushballs, it tends to be delivered deeper than water, increasing the efficiency of the process. Further sinking of the condensates is expected due to cold temperature and ammonia‐ and water‐rich downdrafts formed by the evaporation of mushballs. This process can thus potentially account for the measurements of ammonia depletion in Jupiter’s deep atmosphere.Plain Language SummaryThe Juno mission has revealed that Jupiter’s atmosphere is much more complex and intriguing than previously anticipated. Most of Jupiter’s atmosphere was shown to be depleted in ammonia. While ammonia was expected to be well mixed, large scale variability of ammonia was detected at least 100 km below the cloud level where condensation occurs. We propose a mechanism to explain this depletion and variability. We show that in Jupiter, at very low temperatures (of order −90° C), water ice and ammonia vapor combine to form a liquid and we hypothesize that this subsequently triggers unexpected meteorology. During Jupiter’s violent storms, hailstones form from this liquid, similar to the process in terrestrial storms where hail forms in the presence of supercooled liquid water. Growth of the hailstones creates a slush‐like substance surrounded by a layer of ice, and these “mushballs” fall, evaporate, and continue sinking further in the planet’s deep atmosphere, creating both ammonia depletion and variability, potentially explaining the Juno observations.Key PointsWe show that ammonia can melt water‐ice crystals in Jupiter’s storms and lead to the formation of water‐ammonia hailstones (mushballs)These mushballs and subsequent downdrafts transport ammonia to very deep levelsThis can potentially explain Juno measurements that Jupiter’s ammonia abundance is variable until at least 150 km below the visible cloudsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156131/2/jgre21375.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156131/1/jgre21375_am.pd

Population Structure of Staphylococcus aureus from Remote African Babongo Pygmies

Staphylococcus aureus is a bacterium that colonizes humans worldwide. The anterior nares are its main ecological niche. Carriers of S. aureus are at a higher risk of developing invasive infections. Few reports indicated a different clonal structure and profile of virulence factors in S. aureus isolates from Sub-Saharan Africa. As there are no data about isolates from remote indigenous African populations, we conducted a cross-sectional survey of S. aureus nasal carriage in Gabonese Babongo Pygmies. The isolates were characterized regarding their susceptibility to antibiotic agents, possession of virulence factors and clonal lineage. While similar carriage rates were found in populations of industrialized countries, isolates that encode the genes for the Panton-Valentine leukocidin (PVL) were clearly more prevalent than in European countries. Of interest, many methicillin-susceptible S. aureus isolates from Babongo Pygmies showed the same genetic background as pandemic methicillin-resistant S. aureus (MRSA) clones. We advocate a surveillance of S. aureus in neglected African populations to control the development of resistance to antibiotic drugs with particular respect to MRSA and to assess the impact of the high prevalence of PVL-positive isolates