High-latitude artificial aurora using the EISCAT high-gain HF facility

The EISCAT high-frequency (HF) transmitter facility at Ramfjord, Norway, has been used to accelerate F-region electrons sufficiently to excite the oxygen atoms and nitrogen molecules, resulting in optical emissions at 630, 557.7 and 427.8 nm. During O-mode transmissions at 5.423 MHz, using 630 MW effective radiated power, in the hours after sunset on 12 November 2001 several new observations were made, including: (1) The first high-latitude observation of an HF induced optical emission at 427.8 nm and (2) Optical rings being formed at HF on followed by their collapse into a central blob. Both discoveries remain unexplained with current theories

Efficient Certified Resolution Proof Checking

We present a novel propositional proof tracing format that eliminates complex processing, thus enabling efficient (formal) proof checking. The benefits of this format are demonstrated by implementing a proof checker in C, which outperforms a state-of-the-art checker by two orders of magnitude. We then formalize the theory underlying propositional proof checking in Coq, and extract a correct-by-construction proof checker for our format from the formalization. An empirical evaluation using 280 unsatisfiable instances from the 2015 and 2016 SAT competitions shows that this certified checker usually performs comparably to a state-of-the-art non-certified proof checker. Using this format, we formally verify the recent 200 TB proof of the Boolean Pythagorean Triples conjecture

Optical Waveplates Based on Birefringence of Anisotropic Two-Dimensional Layered Materials

Birefringence is an inherent optical property of anisotropic materials introduced by the anisotropic confinement in their crystal structures. It enables manipulation of light propagation properties (e.g., phase velocity, reflection, and refrac- tion) for various photonic and optoelectronic applications, including waveplates and liquid crystal displays. Two-dimensional (2D) layered materials with high anisotropy are currently gaining an increasing interest for polarization-integrated nano- device applications, which advances the research on birefringent materials. In this article, we investigate the optical birefrin- gence of three anisotropic 2D layered materials (black phosphorus (BP), rhenium disulfide (ReS2), and rhenium diselenide (ReSe2)). We demonstrate that the birefringence in BP (~0.245) is ~ 6 times larger than that of ReS2 (~0.037) and ReSe2 (~0.047) at 520 nm and is comparable to the current state of the art bulk materials (e.g., CaCO3). We use these 2D materials to fabricate atomically-thin optical waveplates and investigate their performance. In particular, for BP, we observe a polarization-plane rotation of ~0.05° per atomic layer at 520 nm. Our results show that the relatively large birefringence of anisotropic 2D layered materials can enable accurate manipulation of light polarization with atomically controlled device thickness for various applications where integrated, nanoscale polarization-controllers are required

High-k GaAs metal insulator semiconductor capacitors passivated by ex-situ plasma-enhanced atomic layer deposited AlN for Fermi-level unpinning

This paper examines the utilization of plasma-enhanced atomic layer deposition grown AlN in the fabrication of a high-kinsulator layer on GaAs. It is shown that high-kGaAsMIS capacitors with an unpinned Fermi level can be fabricated utilizing a thin ex-situ deposited AlNpassivation layer. The illumination and temperature induced changes in the inversion side capacitance, and the maximum band bending of 1.2 eV indicates that the MIS capacitor reaches inversion. Removal of surface oxide is not required in contrast to many common ex-situ approaches.Peer reviewe

Incrementally Computing Minimal Unsatisfiable Cores of QBFs via a Clause Group Solver API

We consider the incremental computation of minimal unsatisfiable cores (MUCs) of QBFs. To this end, we equipped our incremental QBF solver DepQBF with a novel API to allow for incremental solving based on clause groups. A clause group is a set of clauses which is incrementally added to or removed from a previously solved QBF. Our implementation of the novel API is related to incremental SAT solving based on selector variables and assumptions. However, the API entirely hides selector variables and assumptions from the user, which facilitates the integration of DepQBF in other tools. We present implementation details and, for the first time, report on experiments related to the computation of MUCs of QBFs using DepQBF's novel clause group API.Comment: (fixed typo), camera-ready version, 6-page tool paper, to appear in proceedings of SAT 2015, LNCS, Springe

On QBF Proofs and Preprocessing

QBFs (quantified boolean formulas), which are a superset of propositional formulas, provide a canonical representation for PSPACE problems. To overcome the inherent complexity of QBF, significant effort has been invested in developing QBF solvers as well as the underlying proof systems. At the same time, formula preprocessing is crucial for the application of QBF solvers. This paper focuses on a missing link in currently-available technology: How to obtain a certificate (e.g. proof) for a formula that had been preprocessed before it was given to a solver? The paper targets a suite of commonly-used preprocessing techniques and shows how to reconstruct certificates for them. On the negative side, the paper discusses certain limitations of the currently-used proof systems in the light of preprocessing. The presented techniques were implemented and evaluated in the state-of-the-art QBF preprocessor bloqqer.Comment: LPAR 201

Wavelength and pulse duration tunable ultrafast fiber laser mode-locked with carbon nanotubes.

Ultrafast lasers with tunable parameters in wavelength and time domains are the choice of light source for various applications such as spectroscopy and communication. Here, we report a wavelength and pulse-duration tunable mode-locked Erbium doped fiber laser with single wall carbon nanotube-based saturable absorber. An intra-cavity tunable filter is employed to continuously tune the output wavelength for 34 nm (from 1525 nm to 1559 nm) and pulse duration from 545 fs to 6.1 ps, respectively. Our results provide a novel light source for various applications requiring variable wavelength or pulse duration

Relationship of faecal calprotectin and long-term outcomes in Finnish patients with Crohn's disease : retrospective multi-centre chart review study

Background and Aims: A retrospective non-interventional, multi-centre patient chart review study was conducted to investigate the association of faecal calprotectin (FC) 1 year (+/- 2 months) after biological therapy initiation with composite event-free survival (CEFS) consisting of surgical procedures, corticosteroid initiation, treatment failure or dose increase in patients with Crohn's disease (CD). In addition, the correlations of FC and other tests of disease activity were assessed. Materials and methods: Data on Finnish CD patients initiating a biological therapy between 2010 and 2016, were collected. The association of FC and CEFS was analysed with Kaplan-Meier and Cox proportional hazard modelling. The correlations were tested with Pearson's test. Results: Biological therapy was initiated in 186 patients, of which 87 (46.8%) had FC results available at 1 year and 80 had follow-up exceeding 14 months. The characteristics of patients with and without FC results were similar. Patients with elevated FC (>250 mu g/g) had a significantly increased risk of experiencing composite event (HR 3.4, 95% CI: 1.3-8.9; p = .013) when compared to patients with normal FC (FCPeer reviewe

Network development in biological gels: role in lymphatic vessel development

In this paper, we present a model that explains the prepatterning of lymphatic vessel morphology in collagen gels. This model is derived using the theory of two phase rubber material due to Flory and coworkers and it consists of two coupled fourth order partial differential equations describing the evolution of the collagen volume fraction, and the evolution of the proton concentration in a collagen implant; as described in experiments of Boardman and Swartz (Circ. Res. 92, 801–808, 2003). Using linear stability analysis, we find that above a critical level of proton concentration, spatial patterns form due to small perturbations in the initially uniform steady state. Using a long wavelength reduction, we can reduce the two coupled partial differential equations to one fourth order equation that is very similar to the Cahn–Hilliard equation; however, it has more complex nonlinearities and degeneracies. We present the results of numerical simulations and discuss the biological implications of our model

Inkjet Printed Large-Area Flexible Few-Layer Graphene Thermoelectrics

Graphene-based organic nanocomposites have ascended as promising candidates for thermoelectric energy conversion. In order to adopt existing scalable printing methods for developing thermostable graphene-based thermoelectric devices, optimizations of both the material ink and the thermoelectric properties of the resulting films are required. Here, inkjet printed large-area flexible graphene thin films with outstanding thermoelectric properties are reported. The thermal and electronic transport properties of the films reveal the so-called phonon-glass electron-crystal character (i.e. electrical transport behaviour akin to that of few-layer graphene flakes with quenched thermal transport arising from the disordered nanoporous structure). As a result, the all-graphene films show a room-temperature thermoelectric power factor of 18.7 µW m−1 K−2, representing over a three-fold improvement to previous solution-processed all-graphene structures. Our demonstration of inkjet printed thermoelectric devices underscores the potential for future flexible, scalable and low-cost thermoelectric applications, such as harvesting energy from body heat in wearable applications.EPSRC (EP/L016087/1) Royal Academy of Engineering (Graphlex