Stability of the Period-Doubled Core of the 90-degree Partial in Silicon

In a recent Letter [N. Lehto and S. Oberg, Phys. Rev. Lett. 80, 5568 (1998)], Lehto and Oberg investigated the effects of strain fields on the core structure of the 90-degree partial dislocation in silicon, especially the influence of the choice of supercell periodic boundary conditions in theoretical simulations. We show that their results for the relative stability between the two structures are in disagreement with cell-size converged tight-binding total energy (TBTE) calculations, which suggest the DP core to be more stable, regardless of the choice of boundary condition. Moreover, we argue that this disagreement is due to their use of a Keating potential.Comment: 1 page. Submitted to Comments section of PRL. Also available at http://www.physics.rutgers.edu/~dhv/preprints/rn_dcom/index.htm

Lohkoketjuavaimen varmistettu ja suojattu hallintaympäristö

Tiivistelmä. Lohkoketjuteknologia mahdollistaa käyttäjien välisiä transaktioita, sopimuksia ja automaattisesti suoritettavia ohjelmia ilman keskitettyä palvelinta tai kolmatta osapuolta. Samanaikaisesti kun lohkoketjuteknologia vapauttaa sitoutumasta kolmansiin osapuoliin, avainten hallinnasta on muodostumassa merkittävä haaste järjestelmän loppukäyttäjille. Keskitetyissä järjestelmissä käyttäjien avaintietueet ovat yleisesti kolmannen osapuolen hallinnassa ja palautettavissa. Lohkoketjuteknologian ansiosta loppukäyttäjien on mahdollista säilyttää itsellään identifiointiin käytettäviä avaintietueita. Samalla kun kolmansien osapuolten mahdollisuudet väärinkäytöksille vähentyvät, kukaan muu kuin käyttäjä itse ei ole enää vastuussa avaimen turvallisesta säilyttämisestä. Loppukäyttäjän vastuulle jää, että avaimesta on olemassa varmuuskopio, avaimen muodostamiseen käytetään kryptografisesti turvallista satunnaislukugeneraattoria ja ettei kenelläkään toisella ole mahdollisuutta käyttää avainta. Työssä esitellään malli ja ohjelma, jonka avulla avainta säilytetään luotetussa suoritusympäristössä siten että ainoastaan suorittavalla ohjelmalla on mahdollisuus käsitellä avainta. Lisäksi menetelmä tarjoaa mahdollisuuden varmuuskopioida avaimen toisistaan riippumattomia osia ulkopuolisiin tietueisiin, esimerkiksi pilvipalveluihin. Työn toteutus hyödyntää Intel SGX suoritusympäristöä suojaamaan Ethereumissa käytettävää yksityisavainta.Secured and protected management environment for blockchain keys. Abstract. Blockchain technology enables peer-to-peer transactions, contracts and automatically executable programs without centralized server or third party. While blockchain technology removes need of trust to third party, key management is becoming a major challenge for end-users of system. In centralized systems, users’ key records are generally managed and recoverable by third party. Blockchain technology enables end-users to retain key-records used for identification. While opportunities of third party for abuse is diminished, anyone else than the user himself is no longer responsible for the safe storage of the key record. It is the responsibility of end-user to have a backup of the key, use of a cryptographically secure random number generator to generate the key and ensure that no one else has the ability to use that key. The work introduces a model and a program that stores the key in a trusted execution environment so that only the executing program has privilege to utilize the key. In addition, the method provides the ability to back up key as an independent parts to external records, such as cloud services. Implementation of the work utilizes Intel SGX environment to protect Ethereum private key

Sorption competition and kinetics of trivalent cations (Eu, Y and Cm) on corundum (alpha-Al2O3 ) : A batch sorption and TRLFS study

Abstract In this study we have combined batch sorption and laser spectroscopic investigations to study the sorption of Eu(III) and Cm(III), on the aluminum oxide corundum in single- and multi-metal systems. Experiments were performed using a constant equilibrium time as a function of pH (pH-edges) or at constant pH as a function of equilibrium time (kinetic experiments) in 0.01 M NaClO4 and carbonate free conditions. The objective was to investigate how the sorption behavior of trivalent actinides and lanthanides is affected by the presence of another trivalent metal, Y(III). Our hypothesis was that the addition of higher concentrations of trivalent Y(III) together with a chemically similar trivalent metal, Eu(III) or Cm(III), would affect the sorption behavior of that metal. Batch experiments show that when the concentration of competing Y(III) is high enough (1 × 10−4 M) to occupy most of the surface sites, there is a clear shift in the position of the Eu(III) pH-edge to higher pH. Spectroscopic studies using time-resolved laser fluorescence spectroscopy (TRLFS) clearly confirm sorption competition between the trivalent metals Cm(III) and Y(III), but they also indicate a change in the surface speciation of the trivalent actinide in the presence of the competing metal if the concentration of that competing metal is high enough.Peer reviewe

Theoretical study of kinks on screw dislocation in silicon

Theoretical calculations of the structure, formation and migration of kinks on a non-dissociated screw dislocation in silicon have been carried out using density functional theory calculations as well as calculations based on interatomic potential functions. The results show that the structure of a single kink is characterized by a narrow core and highly stretched bonds between some of the atoms. The formation energy of a single kink ranges from 0.9 to 1.36 eV, and is of the same order as that for kinks on partial dislocations. However, the kinks migrate almost freely along the line of an undissociated dislocation unlike what is found for partial dislocations. The effect of stress has also been investigated in order to compare with previous silicon deformation experiments which have been carried out at low temperature and high stress. The energy barrier associated with the formation of a stable kink pair becomes as low as 0.65 eV for an applied stress on the order of 1 GPa, indicating that displacements of screw dislocations likely occur via thermally activated formation of kink pairs at room temperature

Stability of undissociated screw dislocations in zinc-blende covalent materials from first principle simulations

The properties of perfect screw dislocations have been investigated for several zinc-blende materials such as diamond, Si, $\beta$-SiC, Ge and GaAs, by performing first principles calculations. For almost all elements, a core configuration belonging to shuffle set planes is favored, in agreement with low temperature experiments. Only for diamond, a glide configuration has the lowest defect energy, thanks to an sp$^2$ hybridization in the core

Leeway for the loyal: a model of employee discretion

This article examines the factors underlying task discretion from an economist's perspective. It argues that the key axis for understanding discretion is the trade-off between the positive effects of discretion on potential output per employee and the negative effects of greater leeway on work effort. In empirical analysis using matched employer-employee data, it is shown that discretion is strongly affected by the level of employee commitment. In addition, discretion is generally greater in high-skilled jobs, although not without exceptions, and lower where employees are under-skilled. Homeworking and flexitime policies raise employee discretion. The impact of teamworking is mixed. In about half of cases team members do not jointly decide about work matters, and the net effect of teams on task discretion in these cases is negative. In other cases, where team members do decide matters jointly, the impact is found to be neutral according to employees' perceptions, or positive according to managers' perceptions. There are also significant and substantial unobserved establishment-level factors which affect task discretion

Measuring Black Hole Spin in OJ287

We model the binary black hole system OJ287 as a spinning primary and a non-spinning secondary. It is assumed that the primary has an accretion disk which is impacted by the secondary at specific times. These times are identified as major outbursts in the light curve of OJ287. This identification allows an exact solution of the orbit, with very tight error limits. Nine outbursts from both the historical photographic records as well as from recent photometric measurements have been used as fixed points of the solution: 1913, 1947, 1957, 1973, 1983, 1984, 1995, 2005 and 2007 outbursts. This allows the determination of eight parameters of the orbit. Most interesting of these are the primary mass of $1.84\cdot 10^{10} M_\odot$, the secondary mass $1.46\cdot 10^{8} M_\odot$, major axis precession rate $39^\circ.1$ per period, and the eccentricity of the orbit 0.70. The dimensionless spin parameter is $0.28\:\pm\:0.01$ (1 sigma). The last parameter will be more tightly constrained in 2015 when the next outburst is due. The outburst should begin on 15 December 2015 if the spin value is in the middle of this range, on 3 January 2016 if the spin is 0.25, and on 26 November 2015 if the spin is 0.31. We have also tested the possibility that the quadrupole term in the Post Newtonian equations of motion does not exactly follow Einstein's theory: a parameter $q$ is introduced as one of the 8 parameters. Its value is within 30% (1 sigma) of the Einstein's value $q = 1$. This supports the $no-hair theorem$ of black holes within the achievable precision. We have also measured the loss of orbital energy due to gravitational waves. The loss rate is found to agree with Einstein's value with the accuracy of 2% (1 sigma).Comment: 12 pages, 4 figures, IAU26