How solid is solidity? An in-dept study of solidity’s type safety.

Blockchain has evolved a lot in the last years: one of the most important features is the possibility, for mutually untrusted parties, to interact with one another without relying on a third party trusted entity. This interaction is made possible by the so-called smart contracts, passive arbitrary programs executed in a decentralized network and usually manipulating money. One of the main platforms in this sense is Ethereum, and a number of programming languages exist in its ecosystem, all with points of strength and flaws. Of these, the most widely used is for sure Solidity. In spite of its high potential, repeated security concerns have undercut the trust in this way of handling money. Bugs and undesired behaviors are worsened by the impossibility of patching a contract once it is deployed on the blockchain. As a consequence, many analysis tools have been developed by researchers. However, those operating on Solidity lack a real formalization of the core of this language. We aim to fill the gap with Featherweight Solidity (FS). To the best of our knowledge, this is the first calculus including the semantics as well as the type system. Thanks to it, we proved the theorem of Type Safety for Solidity (claimed in the official documentation, although not supported by any public proof). We also formalized, and proved, an extended Type Safety statement addressing groups of transactions. During this process, we found out that Solidity's type system is far from being safe with respect to any type of error: in many occasions, contract interfaces are not consulted at compile-time, and this makes the execution raise an exception and the user waste money. Sometimes, in particular when transferring money from one party to another, exceptions can be avoided by simply looking at, at compile-time, contract interfaces. We also propose an extension of the type system, FS+, that targets this undesired behavior. We prove that Type Safety is maintained, but we formalize additional theorems stating new safety properties, too. In particular, but not only, FS+ statically detects, and consequently rules out, ill-formed money transfers made by means of the Solidity's built-in transfer function. We compared it with Solidity, and showed that including this extension does not change radically the way of writing smart contracts, whereas it makes them much safer.ope

Passive gas-gap heat switch for adiabatic demagnetization refrigerator

A passive gas-gap heat switch for use with a multi-stage continuous adiabatic demagnetization refrigerator (ADR). The passive gas-gap heat switch turns on automatically when the temperature of either side of the switch rises above a threshold value and turns off when the temperature on either side of the switch falls below this threshold value. One of the heat switches in this multistage process must be conductive in the 0.25? K to 0.3? K range. All of the heat switches must be capable of switching off in a short period of time (1-2 minutes), and when off to have a very low thermal conductance. This arrangement allows cyclic cooling cycles to be used without the need for separate heat switch controls

ZnMoO4: a promising bolometer for neutrinoless double beta decay searches

We investigate the performances of two ZnMoO4 scintillating crystals operated as bolometers, in view of a next generation experiment to search the neutrinoless double beta decay of Mo-100. We present the results of the alpha vs beta/gamma discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone. The discrimination capability obtained at the 2615 keV line of Tl-208 is 8 sigma, using the heat-light scatter plot, while it exceeds 20 sigma using the shape of the thermal pulse alone. The achieved FWHM energy resolution ranges from 2.4 keV (at 238 keV) to 5.7 keV (at 2615 keV). The internal radioactive contaminations of the ZnMoO4 crystals were evaluated through a 407 hours background measurement. The obtained limit is < 32 microBq/kg for Th-228 and Ra-226. These values were used for a Monte Carlo simulation aimed at evaluating the achievable background level of a possible, future array of enriched ZnMoO4 crystals.Comment: 9 pages, 8 figure

LA RETE SISMICA DELLA PIANA DI GUIDONIA (LAZIO): DATI PRELIMINARI

After the seismic period during 2001-2002 that has interested the Plain of Guidonia, situated about fifteen kilometres NE of Rome, which events greatest resentment reached the V-VI MCS, have been installed a local seismic purchased by Comune of Guidonia-Montecelio (Rm). The seismic network (RLG) consists of three digital seismic stations with distances of each other about 2 kilometers, activated to leave from the June 2004 and equipped with three components 1 Hz sismometer. Subsequently, the RLG has enriched of other four digital stations equipped with three components 5 Hz sismometer This network has like main objective the high quality data that agree a better definition of the seismic local activity. These data, that integrate those of the Seismographic Centralized National Network (SCNN), agreed a better ipocentre location. Network geometriy was chosen so as to give back the RLG an independent structure to carry out reliable seismicity locations that characterizes the plain of Guidonia. Unfortunately, industrial and human activity, increases in considerable manner the seismic noise, giving back difficult the record of small events. For this motive the location of the sites was more times changed, and lately, after a seismic crisis in the northern side of the Mountains Cornicolani, that has presented with the same features of that of 2001 of Guidonia, some stations were moved in the neighboring village of Palombara Sabina (Rm)

Intense terahertz pulses from SPARC-LAB coherent radiation source

The linac-based Terahertz source at the SPARC_LAB test facility is able to gene rate highly intense Terahertz broadband pulses via coherent transition radiation (CTR) from high brightness electron beams. The THz pulse duration is typically down to 100 fs RMS and can be tuned through the electron bunch duration and shaping. The measured stored energy in a single THz pulse has reached 40 μ J, which corresponds to a peak electric field of 1.6 MV/cm at the THz focus. Here we present the main features, in particular spatial and sp ectral distributions and energy characterizations of the SPARC_LAB THz source, which is very competitive for investigations in Condensed Matter, as well as a valid tool for electron beam longitudinal diagnostics