Quantum dimer model with Z_2 liquid ground-state: interpolation between cylinder and disk topologies and toy model for a topological quantum-bit

We consider a quantum dimer model (QDM) on the kagome lattice which was introduced recently [Phys. Rev. Lett. 89, 137202 (2002)]. It realizes a Z_2 liquid phase and its spectrum was obtained exactly. It displays a topological degeneracy when the lattice has a non-trivial geometry (cylinder, torus, etc). We discuss and solve two extensions of the model where perturbations along lines are introduced: first the introduction of a potential energy term repelling (or attracting) the dimers along a line is added, second a perturbation allowing to create, move or destroy monomers. For each of these perturbations we show that there exists a critical value above which, in the thermodynamic limit, the degeneracy of the ground-state is lifted from 2 (on a cylinder) to 1. In both cases the exact value of the gap between the first two levels is obtained by a mapping to an Ising chain in transverse field. This model provides an example of solvable Hamiltonian for a topological quantum bit where the two perturbations act as a diagonal and a transverse operator in the two-dimensional subspace. We discuss how crossing the transitions may be used in the manipulation of the quantum bit to optimize simultaneously the frequency of operation and the losses due to decoherence.Comment: 11 pages, 7 (.eps) figures. Improved discussion of the destruction of the topological degeneracy and other minor corrections. Version to appear in Phys. Rev.

The last mile: High-Assurance and High-Speed cryptographic implementations

We develop a new approach for building cryptographic implementations. Our approach goes the last mile and delivers assembly code that is provably functionally correct, protected against side-channels, and as efficient as handwritten assembly. We illustrate our approach using ChaCha20Poly1305, one of the two ciphersuites recommended in TLS 1.3, and deliver formally verified vectorized implementations which outperform the fastest non-verified code.We realize our approach by combining the Jasmin framework, which offers in a single language features of high-level and low-level programming, and the EasyCrypt proof assistant, which offers a versatile verification infrastructure that supports proofs of functional correctness and equivalence checking. Neither of these tools had been used for functional correctness before. Taken together, these infrastructures empower programmers to develop efficient and verified implementations by "game hopping", starting from reference implementations that are proved functionally correct against a specification, and gradually introducing program optimizations that are proved correct by equivalence checking.We also make several contributions of independent interest, including a new and extensible verified compiler for Jasmin, with a richer memory model and support for vectorized instructions, and a new embedding of Jasmin in EasyCrypt.This work is partially supported by project ONR N00014-19-1-2292. Manuel Barbosa was supported by grant SFRH/BSAB/143018/2018 awarded by FCT. This work was partially funded by national funds via FCT in the context of project PTDC/CCI-INF/31698/2017

Detailed patient-individual reporting of lymph node involvement in oropharyngeal squamous cell carcinoma with an online interface

Purpose/ObjectiveWhereas the prevalence of lymph node level (LNL) involvement in head & neck squamous cell carcinomas (HNSCC) has been reported, the details of lymphatic progression patterns are insufficiently quantified. In this study, we investigate how the risk of metastases in each LNL depends on the involvement of upstream LNLs, T-category, HPV status and other risk factors.Materials/MethodsWe retrospectively analyzed patients with newly diagnosed oropharyngeal HNSCC treated at a single institution, resulting in a dataset of 287 patients. For all patients, involvement of LNLs I-VII was recorded individually based on available diagnostic modalities (PET, MR, CT, FNA) together with clinicpathological factors. To analyze the dataset, a web-based graphical user interface (GUI) was developed, which allows querying the number of patients with a certain combination of co-involved LNLs and tumor characteristics.ResultsThe full dataset and GUI is part of the publication. Selected findings are: Ipsilateral level IV was involved in 27% of patients with level II and III involvement, but only in 2% of patients with level II but not III involvement. Prevalence of involvement of ipsilateral levels II, III, IV, V was 79%, 34%, 7%, 3% for early T-category patients (T1/T2) and 85%, 50%, 17%, 9% for late T-category (T3/T4), quantifying increasing involvement with T-category. Contralateral levels II, III, IV were involved in 41%, 19%, 4% and 12%, 3%, 2% for tumors for tumors with and without midline extension, respectively. T-stage dependence of LNL involvement was more pronounced in HPV negative than positive tumors, but overall involvement was similar. Ipsilateral level VII was involved in 14% and 6% of patients with primary tumors in the tonsil and the base of tongue, respectively.ConclusionsDetailed quantification of LNL involvement in HNSCC depending on involvement of upstream LNLs and clinicopathological factors may allow for further personalization of CTV-N definition in the future

Shifts in structural diversity of Amazonian forest edges detected using terrestrial laser scanning

Forest edges are an increasingly common feature of Amazonian landscapes due to human-induced forest frag-mentation. Substantial evidence shows that edge effects cause profound changes in forest biodiversity and productivity. However, the broader impacts of edge effects on ecosystem functioning remain unclear. Assessing the three-dimensional arrangement of forest elements has the potential to unveil structural traits that are scalable and closely linked to important functional characteristics of the forest. Using over 600 high-resolution terrestrial laser scanning measurements, we present a detailed assessment of forest structural metrics linked to ecosystem processes such as energy harvesting and light use efficiency. Our results show a persistent change in forest structural characteristics along the edges of forest fragments, which resulted in a significantly lower structural diversity, in comparison with the interior of the forest fragments. These structural changes could be observed up to 35 m from the forest edges and are likely to reflect even deeper impacts on other ecosystem variables such as microclimate and biodiversity. Traits related to vertical plant material allocation were more affected than traits related to canopy height. We demonstrate a divergent response from the forest understory (higher vegetation density close to the edge) and the upper canopy (lower vegetation density close to the edge), indicating that assessing forest disturbances using vertically integrated metrics, such as total plant area index, can lead to an erroneous interpretation of no change. Our results demonstrate the strong potential of terrestrial laser scanning for benchmarking broader-scale (e.g. airborne and space-borne) remote sensing assessments of forest distur-bances, as well as to provide a more robust interpretation of biophysical changes detected at coarser resolutions.Peer reviewe

Forest fragmentation impacts the seasonality of Amazonian evergreen canopies

Predictions of the magnitude and timing of leaf phenology in Amazonian forests remain highly controversial. Here, we use terrestrial LiDAR surveys every two weeks spanning wet and dry seasons in Central Amazonia to show that plant phenology varies strongly across vertical strata in old-growth forests, but is sensitive to disturbances arising from forest fragmentation. In combination with continuous microclimate measurements, we find that when maximum daily temperatures reached 35 °C in the latter part of the dry season, the upper canopy of large trees in undisturbed forests lost plant material. In contrast, the understory greened up with increased light availability driven by the upper canopy loss, alongside increases in solar radiation, even during periods of drier soil and atmospheric conditions. However, persistently high temperatures in forest edges exacerbated the upper canopy losses of large trees throughout the dry season, whereas the understory in these light-rich environments was less dependent on the altered upper canopy structure. Our findings reveal a strong influence of edge effects on phenological controls in wet forests of Central Amazonia.Peer reviewe

Analyse spatiale du processus de localisation à l'aide des fonctions de Ripley

La dégradation des matériaux quasi-fragiles se traduit par l’apparition de micro-fissures qui interagissent, évoluent et coalescent à l’intérieur de la zone d’élaboration (FPZ) pour former une macro-fissure. L’interaction de la FPZ avec les bords de la structure est à l’origine des phénomènes typiques d’effets d’échelle, de bord ou d’écran. Or ces phénomènes mettent en défaut les modèles macroscopiques actuels. Il est donc nécessaire de mieux décrire l’évolution de la FPZ pour prédire la rupture des matériaux quasi-fragiles dans une structure réelle. Les modèles mésoscopiques présentent l’avantage de considérer les détails de la mésostructure et permettent donc de décrire le processus de rupture à l’échelle des hétérogénéités. Un modèle mésoscopique de type lattice 2D est ici adopté. La méso-structure du béton y est idéalisée comme un ensemble de granulats dans une matrice de mortier. Seuls les granulats les plus gros sont considérés explicitement. Les autres granulats sont décrits par l’intermédiaire d’un champ aléatoire auto-corrélé. Le modèle mésoscopique est tout d’abord validé en reproduisant des résultats expérimentaux réalisés sur des poutres de béton en flexion trois points de tailles différentes, entaillées et non-entaillé́es. Il est montré que le modèle permet de prédire la résistance au pic mais aussi de reproduire les phases adoucissantes. Des histogrammes de distances relatives entre points endommagés sont ensuite construits afin d’étudier la corrélation entre évènements successifs. Cette analyse met en évidence des corrélations importantes mais également un fort effet du gradient de déformation en flexion. Pour s’affranchir de cet effet de gradient, le modèle est utilisé en traction simple. Les fonctions de Ripley permettent d’analyser la distribution spatiale des points endommagés au cours de l’essai. Il est montré que cette distribution est initialement pilotée par la structure granulaire, puis qu’elle se propage aléatoirement dans tout l’échantillon avant de se localiser pour former les macro-fissures

UTILLdb, a Pisum sativum in silico forward and reverse genetics tool

UTILLdb is a database of phenotypic and sequence information on mutant genes from a reference Pisum sativum EMS-mutant population