Cubic structures and ideal class groups

We establish a generalization of Breen’s theory of cubic structures on line bundles over group schemes. We study such “n-cubic structures” inductively using multiextensions. As a result we obtain information on the set of isomorphism classes of line bundles with n-cubic structures over finite multiplicative group schemes over Spec (Z) by relating this set to certain corresponding eigenspaces of ideal class groups of cyclotomic fields.

Implementing Volatility Trades in the Athens Derivatives Exchange

The purpose of this paper is to demonstrate how investors can benefit from volatility by constructing portfolios of options and futures based on the FTSE/ASE-20 ADEX listed derivatives. Furthermore, this paper provides an insight into the risks associated with such trades as well as addresses the question of whether such a trade can be profitable when transaction costs and margin requirements are taken into account. Its purpose is to serve as a practical guide to trading volatility using data from the Athens Derivative Exchange. The design of an infoormation systems prototype based on selected trades to measure the expected return on each given trade is also demonstrated. You can use Access or SQL to build the prototype.(In this case I used MSAccess)

Network-Level Performance Evaluation of a Two-Relay Cooperative Random Access Wireless System

In wireless networks relay nodes can be used to assist the users' transmissions to reach their destination. Work on relay cooperation, from a physical layer perspective, has up to now yielded well-known results. This paper takes a different stance focusing on network-level cooperation. Extending previous results for a single relay, we investigate here the benefits from the deployment of a second one. We assume that the two relays do not generate packets of their own and the system employs random access to the medium; we further consider slotted time and that the users have saturated queues. We obtain analytical expressions for the arrival and service rates of the queues of the two relays and the stability conditions. We investigate a model of the system, in which the users are divided into clusters, each being served by one relay, and show its advantages in terms of aggregate and throughput per user. We quantify the above, analytically for the case of the collision channel and through simulations for the case of Multi-Packet Reception (MPR), and we provide insight on when the deployment of a second relay in the system can yield significant advantages.Comment: Submitted for journal publicatio

p-adic shtukas and the theory of global and local Shimura varieties

We establish basic results on p-adic shtukas and apply them to the theory of local and global Shimura varieties, and on their interrelation. We construct canonical integral models for (local, and global) Shimura varieties of Hodge type with parahoric level structure.Comment: 96 pp, comments welcom

On tamely ramified G\mathcal G-bundles on curves

We consider parahoric Bruhat-Tits group schemes over a smooth projective curve and torsors under them. If the characteristic of the ground field is either zero or positive but not too small and the generic fiber is absolutely simple and simply-connected, we show that such group schemes can be written as invariants of reductive group schemes over a tame cover of the curve. We relate the torsors under the Bruhat-Tits group scheme and torsors under the reductive group scheme over the cover which are equivariant for the action of the covering group. For this, we develop a theory of local types for such equivariant torsors. We also relate the moduli stacks of torsors under the Bruhat-Tits group scheme and equivariant torsors under the reductive group scheme over the cover. In an Appendix, B. Conrad provides a proof of the Hasse principle for adjoint groups over function fields with finite field of constants.Comment: with an Appendix by B. Conrad, 35pp. Some corrections, added a hypothesis at small characteristics. To appear in Algebraic Geometr

Robust Sampling for MITL Specifications

Real-time temporal logic reasoning about trajectories of physical systems necessitates models of time which are continuous. However, discrete time temporal logic reasoning is computationally more efficient than continuous time. Moreover, in a number of engineering applications only discrete time models are available for analysis. In this paper, we introduce a framework for testing MITL specifications on continuous time signals using only discrete time analysis. The motivating idea behind our approach is that if the dynamics of the signal fulfills certain conditions and the discrete time signal robustly satisfies the MITL specification, then the corresponding continuous time signal should also satisfy the same MITL specification

Studies on Traction Separation Relations in Fracture of Layered Composites:Experiments and Modeling

Layered fiber reinforced composite materials are prone to fracture in planes parallel to the direction of fibers leading to extensive delamination or intralaminar fracture. This phenomenon of crack propagation is frequently accompanied by significant increase in fracture resistance due to different damage mechanisms active on the wake of the crack. The developed zone comprises intact pulled-out fibers bridging the crack faces forming the so-called, large scale fiber bridging (LSB). Several studies have dealt with the evaluation of the traction-separation relations mainly related to the bridging phenomena in delamination, employing different techniques. However, only a few recent studies dealt with the effect of specimen size on LSB and the traction-separation relations, challenging the applicability of the existing relations in structural design. This work initially focuses on the characterization of LSB phenomena in mode I intralaminar fracture of a unidirectional (UD) carbon fiber reinforced thermoplastic. Here an already developed semi-experimental technique based on quasi-continuous strain measurements by FBG sensors, adapted to the needs of the current study, is employed to identify the traction-separation relation. The outcome of the identification scheme compares very well with the results from a numerical micromechanical virtual test. The identified traction-separation relation is employed to calculate the energy release rate (ERR) and evaluate the resistance curves (R-curves) associated with LSB of this fracture response. An important toughening effect is demonstrated, which is about two times higher than the corresponding interlaminar values. The aforementioned semi-experimental technique is implemented in intralaminar fracture of a UD carbon/epoxy composite and is devoted in evaluating the effect of specimen thickness on the developed closing tractions due to LSB. Here, double cantilever beam (DCB) specimens of three different thicknesses, loaded with end opening forces are employed to conduct the characterization. A significant effect of specimenâs thickness is present on the three identified traction-separation relations. The results of the present study indicate a scaling relationship expressed as a function of the bridging traction profile exponent and the stiffness of the specimen. Nevertheless, a common maximum closing traction at the crack tip is evaluated. Similar to the thermoplastic composite, the measured ERRs are considerably higher than the corresponding interlaminar values. Furthermore, a testing apparatus able to apply pure moments on the bending arms of DCB specimens, by means of pairs of forces is designed, fabricated and used. This testing setup is employed in the fracture characterization of the mentioned carbon/epoxy system to investigate the effect of loading conditions. The acquired results show minor differences on the maximum ERRs, with some small variation on the shape of the R-curves. Finally, the traction-separation relation in delamination of a woven glass fiber reinforced epoxy with tufting through the thickness reinforcement (TTR) is investigated. Accordingly, a generalization of the relation between the closing traction profile and flexural rigidity of the DCB arms is attested and a concise modeling approach for the load history prediction is proposed comprising the effects of LSB and TTR