Designing Secure Ethereum Smart Contracts: A Finite State Machine Based Approach

The adoption of blockchain-based distributed computation platforms is growing fast. Some of these platforms, such as Ethereum, provide support for implementing smart contracts, which are envisioned to have novel applications in a broad range of areas, including finance and Internet-of-Things. However, a significant number of smart contracts deployed in practice suffer from security vulnerabilities, which enable malicious users to steal assets from a contract or to cause damage. Vulnerabilities present a serious issue since contracts may handle financial assets of considerable value, and contract bugs are non-fixable by design. To help developers create more secure smart contracts, we introduce FSolidM, a framework rooted in rigorous semantics for designing con- tracts as Finite State Machines (FSM). We present a tool for creating FSM on an easy-to-use graphical interface and for automatically generating Ethereum contracts. Further, we introduce a set of design patterns, which we implement as plugins that developers can easily add to their contracts to enhance security and functionality

Sequent Calculus in the Topos of Trees

Nakano's "later" modality, inspired by G\"{o}del-L\"{o}b provability logic, has been applied in type systems and program logics to capture guarded recursion. Birkedal et al modelled this modality via the internal logic of the topos of trees. We show that the semantics of the propositional fragment of this logic can be given by linear converse-well-founded intuitionistic Kripke frames, so this logic is a marriage of the intuitionistic modal logic KM and the intermediate logic LC. We therefore call this logic $\mathrm{KM}_{\mathrm{lin}}$. We give a sound and cut-free complete sequent calculus for $\mathrm{KM}_{\mathrm{lin}}$ via a strategy that decomposes implication into its static and irreflexive components. Our calculus provides deterministic and terminating backward proof-search, yields decidability of the logic and the coNP-completeness of its validity problem. Our calculus and decision procedure can be restricted to drop linearity and hence capture KM.Comment: Extended version, with full proof details, of a paper accepted to FoSSaCS 2015 (this version edited to fix some minor typos

Medium-induced gluon radiation and jet quenching in heavy ion collisions

In this brief review, I summarize the new developments on the description of gluon radiation by energetic quarks traversing a medium as well as the observable consequences in high-energy heavy ion collisions. Information about the initial state is essential for a reliable interpretation of the experimental results and will also be reviewed. Comparison with experimental data from RHIC and expectation for the future LHC will be given.Comment: 16 pages, 9 postscript figures. Invited brief review for Modern Physics Letters

Spectroscopic evidence of the formation of (V,Ti)O₂ solid solution in VO₂ thinner films grown on TiO₂(001) substrates

We have prepared VO2 thin films epitaxially grown on TiO2(001) substrates with thickness systematically varied from 2.5 to 13 nm using a pulsed laser deposition method, and studied the transport property and electronic states of the films by means of resistivity and in situ synchrotron photoemission spectroscopy (SRPES). In resistivity measurements, the 13-nm-thick film exhibits a metal-insulator transition at around 290 K on cooling with change of three orders of magnitudes in resistivity. As the film thickness decreases, the metal-insulator transition broadens and the transition temperature increases. Below 4 nm, the films do not show the transition and become insulators. In situ SRPES measurements of near the Fermi level valence band find that the electronic state of the 2.5-nm-thick film is different than that of the temperature-induced insulator phase of VO2 itself although these two states are insulating. Ti 2p core-level photoemission measurements reveal that Ti ions exist near the interface between the films and TiO2 substrates, with a chemical state similar to that in (V,Ti)O-2 solid solution. These results indicate that insulating (V,Ti)O-2 solid solution is formed in the thinner films. We propose a simple growth model of a VO2 thin film on a TiO2(001) substrate. Near the interface, insulating (V,Ti) O-2 solid solution is formed due to the diffusion of Ti ions from the TiO2 substrate into the VO2 film. The concentration of Ti in (V,Ti) O-2 is relatively high near the interface and decreases toward the surface of the film. Beyond a certain film thickness (about 7 nm in the case of the present 13-nm-thick film), the VO2 thin film without any Ti ions starts to grow. Our work suggests that developing a technique for preparing the sharp interface between the VO2 thin films and TiO2 substrates is a key issue to study the physical property of an ultrathin film of "pure" VO2, especially to examine the presence of the novel electronic state called a semi-Dirac point phase predicted by calculations

Discrete Convex Functions on Graphs and Their Algorithmic Applications

The present article is an exposition of a theory of discrete convex functions on certain graph structures, developed by the author in recent years. This theory is a spin-off of discrete convex analysis by Murota, and is motivated by combinatorial dualities in multiflow problems and the complexity classification of facility location problems on graphs. We outline the theory and algorithmic applications in combinatorial optimization problems

Coexistence of Superconductivity and Charge Density Wave in SrPt2As2

SrPt2As2 is a novel arsenide superconductor, which crystallizes in the CaBe2Ge2-type structure as a different polymorphic form of the ThCr2Si2-type structure. SrPt2As2 exhibits a charge-density-wave (CDW) ordering at about 470 K and enters into a superconducting state at Tc = 5.2 K. The coexistence of superconductivity and CDW refers to Peierls instability with a moderately strong electron-phonon interaction. Thus SrPt2As2 can be viewed as a nonmagnetic analog of iron-based superconductors, such as doped BaFe2As2, in which superconductivity emerges in close proximity to spin-density-wave ordering.Comment: 4 pages, 5 figure

Disorder-driven quantum phase transition from antiferromagnetic metal to insulating state in multilayered high-Tc cuprate (Cu,C)Ba2Ca4Cu5Oy

We report on superconducting(SC) characteristics for oxygen-reduced Cu-based five-layered high-temperature superconductor (Cu,C)Ba2Ca4Cu5Oy(Cu-1245(OPT)), which includes five-fold outer planes (OP) and four-fold inner planes (IP).As a result of the reduction of the carrier density, the bulk SC for Cu-1245 (OPT) takes place at the nearly optimally-doped OP with Tc= 98 K that is different from previously-reported Cu-1245(OVD) where IP plays a primary role for the onset of SC. It gives an evidence that the carrier density of the optimally-doped layer determines its bulk Tc.Static antiferromagnetic(AFM) order is evidenced at IP's by zero-field Cu-NMR at low temperature, irrespective of the SC transition at OP's below 98K. This AFM state at IP's is characterized by a carrier localization at low temperatures due to disorder effect, whereas the carrier densities in each layer are similar to Hg-1245(OPT) where the AFM metallic state are realized in IP's. This finding reinforces the phase diagram in which the AFM metallic phase exists between AFM insulator and SC states for the case of ideally-flat CuO2 plane without disorder.Comment: 4 pages, 5 figure

Observation of Very High Energy Gamma Rays from HESS J1804-216 with CANGAROO-III Telescopes

We observed the unidentified TeV gamma-ray source HESS J1804-216 with the CANGAROO-III atmospheric Cerenkov telescopes from May to July in 2006. We detected very high energy gamma rays above 600 GeV at the 10 sigma level in an effective exposure of 76 hr. We obtained a differential flux of (5.0+/-1.5_{stat}+/-1.6_{sys})\times 10^{-12}(E/1 TeV)^{-\alpha} cm^{-2}s^{-1}TeV^{-1} with a photon index \alpha of 2.69 +/- 0.30_{stat} +/- 0.34_{sys}, which is consistent with that of the H.E.S.S. observation in 2004. We also confirm the extended morphology of the source. By combining our result with multi-wavelength observations, we discuss the possible counterparts of HESS J1804-216 and the radiation mechanism based on leptonic and hadronic processes for a supernova remnant and a pulsar wind nebula.Comment: 11 pages, 12 figures, Accepted in Ap

Influence of impurity-scattering on tunneling conductance in d-wave superconductors with broken time reversal symmetry

Effects of impurity scattering on tunneling conductance in dirty normal-metal/insulator/superconductor junctions are studied based on the Kubo formula and the recursive Green function method. The zero-bias conductance peak (ZBCP) is a consequence of the unconventional pairing symmetry in superconductors. The impurity scattering in normal metals suppresses the amplitude of the ZBCP. The degree of the suppression agrees well with results of the quasiclassical Green function theory. When superconductors have $d$+is-wave pairing symmetry, the time-reversal symmetry is broken in superconductors and the ZBCP splits into two peaks. The random impurity scattering reduces the height of the two splitting peaks. The position of the splitting peaks, however, almost remains unchanged even in the presence of the strong impurity scattering. Thus the two splitting peaks never merge into a single ZBCP.Comment: 12 pages, 5 figures, using jpsj2.cls and overcite.st