A Semantic Framework for the Security Analysis of Ethereum smart contracts

Smart contracts are programs running on cryptocurrency (e.g., Ethereum) blockchains, whose popularity stem from the possibility to perform financial transactions, such as payments and auctions, in a distributed environment without need for any trusted third party. Given their financial nature, bugs or vulnerabilities in these programs may lead to catastrophic consequences, as witnessed by recent attacks. Unfortunately, programming smart contracts is a delicate task that requires strong expertise: Ethereum smart contracts are written in Solidity, a dedicated language resembling JavaScript, and shipped over the blockchain in the EVM bytecode format. In order to rigorously verify the security of smart contracts, it is of paramount importance to formalize their semantics as well as the security properties of interest, in particular at the level of the bytecode being executed. In this paper, we present the first complete small-step semantics of EVM bytecode, which we formalize in the F* proof assistant, obtaining executable code that we successfully validate against the official Ethereum test suite. Furthermore, we formally define for the first time a number of central security properties for smart contracts, such as call integrity, atomicity, and independence from miner controlled parameters. This formalization relies on a combination of hyper- and safety properties. Along this work, we identified various mistakes and imprecisions in existing semantics and verification tools for Ethereum smart contracts, thereby demonstrating once more the importance of rigorous semantic foundations for the design of security verification techniques.Comment: The EAPLS Best Paper Award at ETAP

Xenogeneic, extracorporeal liver perfusion in primates improves the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio)

In fulminant hepatic failure (FHF), the development of hepatic encephalopathy is associated with grossly abnormal concentrations of plasma amino acids (PAA). Normalization of the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio) correlates with clinical improvement. This study evaluated changes in PAA metabolism during 4 h of isolated, normothermic extracorporeal liver perfusion using a newly designed system containing human blood and a rhesus monkey liver. Bile and urea production were within the physiological range. Release of the transaminases AST, ALT and LDH were minimal. The ratio of branched (valine, leucine, isoleucine) to aromatic (tyrosine, phenylalanine) amino acids increased significantly. These results indicate that a xenogeneic extracorporeal liver perfusion system is capable of significantly increasing Fischer's ratio and may play a role in treating and bridging patients in FHF in the future

Generalized Swiss-cheese cosmologies: Mass scales

We generalize the Swiss-cheese cosmologies so as to include nonzero linear momenta of the associated boundary surfaces. The evolution of mass scales in these generalized cosmologies is studied for a variety of models for the background without having to specify any details within the local inhomogeneities. We find that the final effective gravitational mass and size of the evolving inhomogeneities depends on their linear momenta but these properties are essentially unaffected by the details of the background model.Comment: 10 pages, 14 figures, 1 table, revtex4, Published form (with minor corrections

Synthesis Of Carbon Nitride Films At Low Temperatures

Carbon nitride films (CN x) have been deposited by sputtering a graphite target with nitrogen ions. Films were grown both with and without the presence of an assisting focused N 2 ion beam. The sputter beam voltage was varied between 150 and 1500 V and the applied assisting beam voltage from 80 to 500 V. The substrate was held at fixed temperatures between 80 and 673 K. The coatings were characterized with respect to their electrical, optical, and structural properties. The nitrogen content was measured by x-ray photoelectron spectroscopy (XPS) and a maximum nitrogen concentration of 44 at. % was obtained for a nonassisted sample deposited at 140 K. The chemical structure was investigated by XPS and Fourier transform infrared spectroscopy. Reduction of the substrate temperature in conjunction with low sputter beam voltages (<200 V) caused the optical band gap to increase up to 2.2 eV, the sheet conductivity to decrease to less th an 10 -9 (Ω cm) -1 and the density to be reduced to 1.6 g/cm 3. The increasing transparency is accompanied by structural changes indicating a transition from a predominantly sp 2 bonded amorphous sp 2/sp 3 C-N network to a more linear polymerlike structure consisting predominantly of doubly and triply bonded C and N atoms. No evidence for the formation of the β-C 3N 4 phase was found. © 1997 American Vacuum Society.151107112Hammer, P., Gissler, W., (1996) Diam. Relat. Mater., 5, p. 1152Hammer, P., Baker, M.A., Lenardi, C., Gissler, W., Thin Solid Films, , to be publishedTodorov, S.S., Marton, D., Boyd, K.J., Al-Bayati, A.H., Rabalais, J.W., (1994) J. Vac. Sci. Technol. A, 12, p. 3192Liu, A.Y., Cohen, M.L., (1990) Phys. Rev. B, 41, p. 10727Baker, M.A., Hammer, P., Surf. Interface Anal., , submittedKaufman, J.H., Metin, S., Saperstein, D.D., (1989) Phys. Rev. B, 39, p. 13053Dolphin, D., Wick, A., (1977) Tabulation of Infrared Spectral Data, , Wiley, New YorkSocrates, G., (1980) Infrared Characteristic Group Frequencies, , Wiley, Chichester, U.KSjöström, H., Stafström, S., Boman, M., Sundgren, J.E., (1995) Phys. Rev. Lett., 75, p. 1336Marton, D., Al-Bayati, A.H., Todorov, S.S., Boyd, K.J., Rabalais, J.W., (1994) Nucl. Instrum. Methods Phys. Res. B, 90, p. 277Sjöström, H., Hultman, L., Sundgren, J.-E., Hainsworth, S.V., Page, T.F., Theunissen, G.S.A.M., (1996) J. Vac. Sci. Technol. A, 14, p. 56Briggs, D., Clark, D.T., Keable, H.R., Kilner, M., (1973) J. Chem. Soc. Dalton Trans., p. 2143Barber, M., Conner, J.A., Guest, M.F., Hillier, I.H., Schwartz, M., Stacey, M., (1973) J. Chem. Soc. Faraday Trans. II, 69, p. 551Bircumshaw, L.L., Tayler, F.M., Whiffen, D.H., (1954) J. Chem. Soc., p. 93

Adlayer core-level shifts of random metal overlayers on transition-metal substrates

We calculate the difference of the ionization energies of a core-electron of a surface alloy, i.e., a B-atom in a A_(1-x) B_x overlayer on a fcc-B(001)-substrate, and a core-electron of the clean fcc-B(001) surface using density-functional-theory. We analyze the initial-state contributions and the screening effects induced by the core hole, and study the influence of the alloy composition for a number of noble metal-transition metal systems. Data are presented for Cu_(1-x)Pd_x/Pd(001), Ag_(1-x) Pd_x/Pd(001), Pd_(1-x) Cu_x/Cu(001), and Pd_(1-x) Ag_x/Ag(001), changing x from 0 to 100 %. Our analysis clearly indicates the importance of final-state screening effects for the interpretation of measured core-level shifts. Calculated deviations from the initial-state trends are explained in terms of the change of inter- and intra-atomic screening upon alloying. A possible role of alloying on the chemical reactivity of metal surfaces is discussed.Comment: 4 pages, 2 figures, Phys. Rev. Letters, to appear in Feb. 199

Unitary and analytic model of nucleon EM structure, the puzzle with JLab proton polarization data and new insight into proton charge distribution

The Unitary and analytic model of nucleon electromagnetic structure, describing all existing nucleon form factor data, is briefly reviewed. Then in the framework of this model the problem of inconsistency of older proton electric form factor data in space-like region (obtained from $e^{-}p$ process by the Rosenbluth technique) with recent Jefferson Lab data on the ratio $G_{Ep}(t)/G_{Mp}(t)$ (measured in precise polarization $\overrightarrow{e}^{-}p\to e^{-}\overrightarrow{p}$ experiment) is suggested to be solved in favour of the latter data which, however, unlike older data cause an existence of the form factor zero, i.e. a difraction minimum in $|G_{Ep}(t)|$ around $t=-Q^{2}=-13$GeV$^{2}$. The new behaviour of $G_{Ep}(t)$ with the zero gives modified proton charge distribution with enlarged value of the mean square charge radius.Comment: 9 pages, 11 eps figures. Talk presented at the workshop on Lepton Scattering and the Structure of Hadrons and Nuclei, Erice (Italy), September 200

Evaluation der potenziellen Regeneratschädigung bei der Kallusumformung nach Distraktionsosteogenese der Mandibula: Eine experimentelle Untersuchung am Tiermodell

Zusammenfassung: Ziel: Bei der Korrektur dreidimensionaler Deformitäten des Gesichtsskelettes mit der Distraktionsosteogenese werden Umformungsvorgänge des Regenerates einerseits als Bestandteil des Behandlungsplans, andererseits im Falle eines Verlustes der Kontrolle über den Distraktionsvektor vorgenommen. Die vorliegende Untersuchung hatte das Ziel, die Grenzen der Kallusmanipulation zu beurteilen. Dazu wurden die Auswirkungen komprimierender sowie dehnender Einflüsse am gleichen Regenerat untersucht. Material und Methode: Bei 15Beagle-Hunden wurde mit speziell angefertigten bidirektionalen Distraktoren eine lineare Distraktion von 10mm beidseits im Unterkieferwinkel vorgenommen. Der neu gebildete Kallus wurde in einem Schritt um 20° anguliert, was im vorliegenden Modell einer Verkürzung/Verlängerung von ca. 35% der Ausgangslänge des Regenerates gleichkommt. Die Position des Rotationszentrums erlaubte es, das Regenerat gleichzeitig zu komprimieren und zu dehnen. Die Auswirkungen dieser mechanischen Einflüsse auf die Ossifikation des Regenerates wurden nach 6 bzw. 13Wochen beurteilt und mit einer Kontrollgruppe, bei der lediglich eine lineare Distraktion durchgeführt worden war, verglichen. Ergebnisse: Die radiologischen und histologischen Untersuchungen ergaben keinen statisch signifikanten Unterschied zwischen dem komprimierten und gedehnten Regenerat. Es zeigten sich jedoch im gedehnten Sektor des Kallus Zonen unvollständiger Ossifikation nach 6-wöchiger Konsolidierungszeit. Unter stabilen Verhältnissen wurde die verzögerte Knochenheilung im weiteren Verlauf kompensiert und eine vollständige Ossifikation nach 13Wochen erreicht. Schlussfolgerung: Unter stabilen Verhältnissen kann ein durch Distraktion gebildetes frisches Regenerat in einem beträchtlichen Ausmaß umgeformt werden, ohne die knöcherne Heilung bleibend zu kompromittieren. Die Dehnung des Kallus kann jedoch zu einer Verzögerung oder dem Ausbleiben des Ossifikationsprozesses führen und sollte vermieden werden. Dies lässt sich durch eine Überkorrektur der Regeneratlänge oder durch eine graduelle Angulation während des Distraktionsvorgangs erreiche

Using resource graphs to represent conceptual change

We introduce resource graphs, a representation of linked ideas used when reasoning about specific contexts in physics. Our model is consistent with previous descriptions of resources and coordination classes. It can represent mesoscopic scales that are neither knowledge-in-pieces or large-scale concepts. We use resource graphs to describe several forms of conceptual change: incremental, cascade, wholesale, and dual construction. For each, we give evidence from the physics education research literature to show examples of each form of conceptual change. Where possible, we compare our representation to models used by other researchers. Building on our representation, we introduce a new form of conceptual change, differentiation, and suggest several experimental studies that would help understand the differences between reform-based curricula.Comment: 27 pages, 14 figures, no tables. Submitted for publication to the Physical Review Special Topics Physics Education Research on March 8, 200

IMAGES I. Strong evolution of galaxy kinematics since z=1

(abbreviated) We present the first results of the ESO large program, ``IMAGES'' which aims at obtaining robust measurements of the kinematics of distant galaxies using the multi-IFU mode of GIRAFFE on the VLT. 3D spectroscopy is essential to robustly measure the often distorted kinematics of distant galaxies (e.g., Flores et al. 2006). We derive the velocity fields and $\sigma$-maps of 36 galaxies at 0.4<z<0.75 from the kinematics of the [OII] emission line doublet, and generate a robust technique to identify the nature of the velocity fields based on the pixels of the highest signal-to-noise ratios (S/N). We have gathered a unique sample of 63 velocity fields of emission line galaxies (W0([OII]) > 15 A) at z=0.4-0.75, which are a representative subsample of the population of M_stellar>1.5x10^{10} M_sun emission line galaxies in this redshift range, and are largely unaffected by cosmic variance. Taking into account all galaxies -with or without emission lines- in that redshift range, we find that at least 41+/-7% of them have anomalous kinematics, i.e., they are not dynamically relaxed. This includes 26+/-7% of distant galaxies with complex kinematics, i.e., they are not simply pressure or rotationally supported. Our result implies that galaxy kinematics are among the most rapidly evolving properties, because locally, only a few percent of the galaxies in this mass range have complex kinematics.Comment: 17 pages, 6 figures, Accepted by A&