Molecular Dynamics Study of Nanoribbon Formation by Encapsulating Cyclic Hydrocarbon Molecules inside Single-Walled Carbon Nanotube

Carbon nanotubes filled with organic molecules can serve as chemical nanoreactors. Recent experimental results show that, by introducing cyclic hydrocarbon molecules inside carbon nanotubes, they can be transformed into nanoribbons or inner tubes, depending on the experimental conditions. In this paper, we present our results obtained as a continuation of our previous molecular dynamics simulation work. In our previous work, the initial geometry consisted of independent carbon atoms. Now, as an initial condition, we have placed different molecules inside a carbon nanotube (18,0): C5H5 (fragment of ferrocene), C5, C5+H2; C6H6 (benzene), C6, C6+H2; C20H12 (perylene); and C24H12 (coronene). The simulations were performed using the REBO-II potential of the LAMMPS software package, supplemented with a Lennard-Jones potential between the nanotube wall atoms and the inner atoms. The simulation proved difficult due to the slow dynamics of the H abstraction. However, with a slight modification of the parameterization, it was possible to model the formation of carbon nanoribbons inside the carbon nanotube.

Formation of nanoribbons by carbon atoms confined in a single-walled carbon nanotube-A molecular dynamics study

Carbon nanotubes can serve as one-dimensional nanoreactors for the in-tube synthesis of various nanostructures. Experimental observations have shown that chains, inner tubes, or nanoribbons can grow by the thermal decomposition of organic/organometallic molecules encapsulated in carbon nanotubes. The result of the process depends on the temperature, the diameter of the nanotube, and the type and amount of material introduced inside the tube. Nanoribbons are particularly promising materials for nanoelectronics. Motivated by recent experimental results observing the formation of carbon nanoribbons inside carbon nanotubes, molecular dynamics calculations were performed with the open source LAMMPS code to investigate the reactions between carbon atoms confined within a single-walled carbon nanotube. Our results show that the interatomic potentials behave differently in quasi-one-dimensional simulations of nanotube-confined space than in three-dimensional simulations. In particular, the Tersoff potential performs better than the widely used Reactive Force Field potential in describing the formation of carbon nanoribbons inside nanotubes. We also found a temperature window where the nanoribbons were formed with the fewest defects, i.e., with the largest flatness and the most hexagons, which is in agreement with the experimental temperature range.

Observation of competing, correlated ground states in the flat band of rhombohedral graphite

In crystalline solids, the interactions of charge and spin can result in a variety of emergent quantum ground states, especially in partially filled, topological flat bands such as Landau levels or in "magic angle" graphene layers. Much less explored is rhombohedral graphite (RG), perhaps the simplest and structurally most perfect condensed matter system to host a flat band protected by symmetry. By scanning tunneling microscopy, we map the flat band charge density of 8, 10, 14, and 17 layers and identify a domain structure emerging from a competition between a sublattice antiferromagnetic insulator and a gapless correlated paramagnet. Our density matrix renormalization group calculations explain the observed features and demonstrate that the correlations are fundamentally different from graphene-based magnetism identified until now, forming the ground state of a quantum magnet. Our work establishes RG as a platform to study many-body interactions beyond the mean-field approach, where quantum fluctuations and entanglement dominate.

Signature of Large-Gap Quantum Spin Hall State in the Layered Mineral Jacutingaite

Quantum spin Hall (QSH) insulators host edge states, where the helical locking of spin and momentum suppresses backscattering of charge carriers, promising applications from low-power electronics to quantum computing. A major challenge for applications is the identification of large gap QSH materials, which would enable room temperature dissipationless transport in their edge states. Here we show that the layered mineral jacutingaite (Pt₂HgSe₃) is a candidate QSH material, realizing the long sought-after Kane-Mele insulator. Using scanning tunneling microscopy, we measure a band gap in excess of 100 meV and identify the hallmark edge states. By calculating the [Formula: see text] invariant, we confirm the topological nature of the gap. Jacutingaite is stable in air, and we demonstrate exfoliation down to at least two layers and show that it can be integrated into heterostructures with other two-dimensional materials. This adds a topological insulator to the 2D quantum material library.

Deaths of despair and Brexit votes: cross-local authority statistical analysis in England and Wales

Objectives

To test the hypothesis that ‘deaths of despair’, a marker of social suffering, was associated with greater support for Brexit in the UK’s 2016 EU referendum.

Methods

Cross local authority regression models of 2016 Brexit referendum vote shares for each local authority in England and Wales on changes in rates of suicide and drug-related deaths pre- (2005-2007) and post-recession (2014-2016), adjusting for several socioeconomic and demographic factors.

Survey population: 345 local authorities in England and Wales.

Results

Greater mortality rates from deaths of despair were significantly associated with higher Brexit vote shares. In unadjusted models, an increase of 10 drug-related deaths per 100 000 associated with a 13.20 percentage point increase in Brexit votes (95% CI: 7.09 to 19.31), while an increase of 10 suicides per 100 000 was associated with a 9.93 percentage point increase in vote shares for Brexit (95% confidence interval 6.21 to 13.65). These associations are explained by local area-level economic and education factors.

Conclusions

Worsening external causes of death correlate with Brexit voting. Such deaths may serve as an early warning indicator for political instability.

Key messages

Prior research has shown correlations between deaths of despair and votes shares for Trump in the 2016 US presidential election. We extend this research to the UK, showing that greater mortality rates from deaths of despair were significantly associated with higher Brexit vote shares.

Uniaxial strain induced topological phase transition in bismuth-tellurohalide-graphene heterostructures

We explore the electronic structure and topological phase diagram of heterostructures formed of graphene and ternary bismuth tellurohalide layers. We show that mechanical strain inherently present in fabricated samples could induce a topological phase transition in single-sided heterostructures, turning the sample into a novel experimental realisation of a time reversal invariant topological insulator. We construct an effective tight binding description for low energy excitations and fit the model's parameters to ab initio band structures. We propose a simple approach for predicting phase boundaries as a function of mechanical distortions and hence gain a deeper understanding on how the topological phase in the considered system may be engineered.

Enhanced NMR relaxation of Tomonaga-Luttinger liquids and the magnitude of the carbon hyperfine coupling in single-wall carbon nanotubes

Recent transport measurements [Churchill et al. Nature Phys. 5, 321 (2009)] found a surprisingly large, 2-3 orders of magnitude larger than usual (13)C hyperfine coupling (HFC) in (13)C enriched single-wall carbon nanotubes. We formulate the theory of the nuclear relaxation time in the framework of the Tomonaga-Luttinger liquid theory to enable the determination of the HFC from recent data by Ihara et al. [Europhys. Lett. 90, 17,004 (2010)]. Though we find that 1/T(1) is orders of magnitude enhanced with respect to a Fermi-liquid behavior, the HFC has its usual, small value. Then, we reexamine the theoretical description used to extract the HFC from transport experiments and show that similar features could be obtained with HFC-independent system parameters.

Umbilical cord as temporary coverage in gastroschisis

INTRODUCTION

Although the early definitive closure of gastroschisis is possible in many cases, there is an ongoing discussion about the advantages of staged reduction. Different strategies and materials have been described to wrap the bowel for protection and reduce heat and fluid loss. The variety of devices ranges from prosthetic patches to biomaterials. We present use of the umbilical cord for temporary coverage in primarily irreducible gastroschisis.

METHOD

After revision and reduction of as much gut as possible under constant monitoring of the bladder pressure, the remaining eviscerated intestine is covered by the longitudinally split umbilical cord. Over the following days the continued reduction of the bowel relies on gravity, assisted by progressive compression by the shrinking umbilical cord tissue. At 10 days after performing the umbilical cord flap, it is possible to close the fascia without complications using gentle pressure.

RESULTS

Since 1991 we have used this umbilical cord flap for staged reduction in 17 infants (10 females, 7 males) with giant gastroschisis. There were no complications related to use of the umbilical cord flap, no infections or NEC episodes, and no mortality. Length of hospital stay was 5 weeks on average. In 3 patients the course was complicated by associated defects or an underlying malformation.

CONCLUSION

Our experience confirms the advantage of a staged reduction in giant gastroschisis. The use of autogenic material such as the umbilical cord has advantages such as low infection rates and easy availability.

Oxygen-isotope labeled titania: Ti(18)O2

(18)O-isotope labelled titania (anatase, rutile) was synthesized. The products were characterized by Raman spectra together with their quantum chemical modelling. The interaction with carbon dioxide was investigated using high-resolution FTIR spectroscopy, and the oxygen isotope exchange at the Ti(18)O(2)/C(16)O(2) interface was elucidated.

Electron spin resonance signal of Luttinger liquids and single-wall carbon nanotubes

A comprehensive theory of electron spin resonance (ESR) for a Luttinger liquid state of correlated metals is presented. The ESR measurables such as the signal intensity and the linewidth are calculated in the framework of Luttinger liquid theory with broken spin rotational symmetry as a function of magnetic field and temperature. We obtain a significant temperature dependent homogeneous line broadening which is related to the spin-symmetry breaking and the electron-electron interaction. The result crosses over smoothly to the ESR of itinerant electrons in the noninteracting limit. These findings explain the absence of the long-sought ESR signal of itinerant electrons in single-wall carbon nanotubes when considering realistic experimental conditions.

Nonparasitic splenic cysts in children: a multicentric study

PURPOSE

Nonparasitic splenic cysts (NPSCs) are uncommon in children. The aim of this multinational and multicentric study was to present the authors' experience as well as the changing trends in the management of NPSCs over the last 25 years.

MATERIAL AND METHODS

From 1981 to 2005, 50 children or adolescents were surgically treated for NPSCs in 6 paediatric surgical centres in four European countries. The medical records of these 50 patients with NPSCs were reviewed retrospectively.

RESULTS

Twenty-six male and 24 female patients were operated on. Age at surgery ranged from 1 to 17 years (mean 11.9). Seventeen patients were symptomatic. Six total (4 open and 2 laparoscopic) and 26 partial (22 open and 4 laparoscopic) splenectomies were performed. Laparoscopic fenestration or deroofing and open cystectomy was carried out in 9 patients, respectively. Histological findings revealed the lesion to be an epidermoid cyst (n = 28), a pseudocyst (n = 15) or a mesothelial cyst (n = 2). In 5 patients haemangioma or lymphangioma was the pathological diagnosis. At a mean follow-up of 2.9 years, residual cysts were found in 8 laparoscopically treated patients, 4 of whom required re-do laparoscopy or open surgery.

CONCLUSIONS

Over the last two decades, the surgical treatment of NPSCs has changed from a formerly customary total splenectomy to spleen-conserving procedures, such as total cystectomy with or without partial splenectomy or partial cystectomy. These therapeutic modalities can be performed laparoscopically, if technically possible. Fenestration or deroofing of the cyst resulted in a high recurrence rate (7/9).

Proximity-induced subgaps in andreev billiards

We examine the density of states of an Andreev billiard and show that any billiard with a finite upper cutoff in the path length distribution P(s) will possess an energy gap on the scale of the Thouless energy. An exact quantum mechanical calculation for different Andreev billiards gives good agreement with the semiclassical predictions when the energy dependent phase shift for Andreev reflections is properly taken into account. Based on this new semiclassical Bohr-Sommerfeld approximation of the density of states, we derive a simple formula for the energy gap. We show that the energy gap, in units of Thouless energy, may exceed the value predicted earlier from random matrix theory for chaotic billiards.

Negative length orbits in normal-superconductor billiard systems

The path-length spectra of mesoscopic systems including diffractive scatterers and connected to a superconductor are studied theoretically. We show that the spectra differ fundamentally from that of normal systems due to the presence of Andreev reflection. It is shown that negative path lengths should arise in the spectra as opposed to the normal system. To highlight this effect we carried out both quantum mechanical and semiclassical calculations for the simplest possible diffractive scatterer. The most pronounced peaks in the path-length spectra of the reflection amplitude are identified by the routes that the electron and/or hole travels.