Search for Bs -> mu mu and B0 -> mu mu decays in CMS

A search for the rare decays (Bs -> \mu \mu) and (B0 -> \mu\mu) performed in pp collisions at sqrt{s} = 7 TeV is presented. The data sample, collected by the CMS experiment at the LHC, corresponds to an integrated luminosity of 1.14 /fb. In both cases the number of events observed after all selection requirements is consistent with expectations from background and standard model signal predictions. The resulting upper limits on the branching fractions are BF(Bs -> \mu\mu) \mu \mu) < 4.6 * 10^{-9} at 95% confidence level (CL). Furthermore, the combination of the results of the search for the decay (Bs -> \mu \mu) by the CMS and LHCb experiments is presented. The combined upper limit is BF < 1.1 * 10^{-8} at 95% CL.Comment: Presented at the 2011 Hadron Collider Physics symposium (HCP-2011), Paris, France, November 14-18 2011, 3 pages, 5 figur

Wide energy band gap materials for next generation heterojunction solar cells

Due to the increase of energy demand and the growth of atmospheric pollution, in the last few years renewable energy sources had a large growth. Among these, photovoltaic solar cells played a central role, thanks to the reduction of their cost partially due to the wide research developed on them. Currently, silicon crystalline solar cells’ state of the art is based on heterojunction structures that combines crystalline silicon with a wider band gap semiconductor material like hydrogenate amorphous silicon (a-Si:H). This technology detains current efficiency record of 26.7 %. However, this structure has still certain aspects that can be improved such as the high light absorption of the amorphous silicon layers (a-Si:H), which limits the overall energy that can be converted into current, and their low thermal stability, which does not allow to overcome their deposition temperature (typically 200°C) in the following fabrication steps, limiting and making more difficult and costly their fabrication. Furthermore, during the amorphous silicon layers’ deposition, some highly hazardous and toxic gases are used and it would be desired to find an alternative. In this work are studied two new materials that can help to overcome the aforementioned drawbacks of amorphous silicon layers. The first material is hydrogenated amorphous Silicon sub-Oxide (a-SiOx:H) which during this work was demonstrated to be more transparent and more thermally stable than a-Si:H, preserving the passivation properties of amorphous silicon layers. Different heterojunction solar cells based both on a-SiOx:H and a-Si:H were made and characterized, confirming the higher transparency and thermal stability of the former set with respect to the latter group. Furthermore it was proved the compatibility between deposition process of a-SiOx:H and a-Si:H, confirming this material as a suitable candidate to replace amorphous silicon layers in industry. Moreover, thanks to the oxygen presence inside the film, the a-SiOx:H layers showed a high chemically compatibility with metal oxides which, may be suitable to replace a-Si:H layers as selective contacts in case they have a high work function. Among these metal oxides it was chosen non-stoichiometric Molybdenum Oxide (MoOx) as a second material to be investigated, since unlike doped a-Si:H layer does not need the use of hazardous and toxic gases during the deposition process. MoOx layer was investigated in terms of material analysis and its characteristics and was developed together with a-SiOx:H layer to obtain high transparency and stability at industrial level. Hence the MoOx layer was successfully experimented in combination with a-SiOx:H buffer inside a complete heterojunction solar cell which was described and characterized, exploiting their high overall transparency allowing the absorption of a wider portion of sunlight spectrum in comparison to heterojunction solar cells based on a-Si:H layers. The experimental work of my Ph.D. thesis has been mainly carried out at the “ENEA Casaccia” laboratories, some experiments have been performed at “ENEA Portici” laboratories

Stochastic Ray Propagation in Stratified Random Lattices – Comparative Assessment of Two Mathematical Approaches

In this report, ray propagation in stratified semi-infinite percolation lattices consisting of a succession of uniform density layers is considered. The final version of this article is available at the url of the journal PIER: http://www.jpier.org/PIER

Computationally-Effective Optimal Excitation Matching for the Synthesis of Large Monopulse Arrays

Antenna arrays able to generate two different patterns are widely used in tracking radar systems [1]. Optimal (in the Dolph�]Chebyshev sense) sum [2] and difference patterns [3] can be generated by using two independent feed networks. Unfortunately, such a situation generally turns out to be impracticable because of its costs, the occupied physical space, the circuit complexity, and electromagnetic interferences. Thus, starting from the optimal sum pattern a sub�]optimal solution for the difference pattern is usually synthesized by means of the sub�]array technique. The array elements are grouped in sub�]arrays properly weighted for matching the constrains of the difference beam. Finding the best elements grouping and the sub�]array weights is a complex and challenging research topic, especially when dealing with large arrays. As far as linear arrays are concerned, McNamara proposed in [4] an analytical method for determining the �gbest compromise�h difference pattern. Unfortunately, when the ratio between the elements of the array and sub�]arrays increases, such a technique exhibits several limitations mainly due to the ill�]conditioning of the problem and the computational costs due to exhaustive evaluations. A non�]negligible saving might be achieved by applying optimization algorithms (see for instance [5] and [6]) aimed at minimizing a suitable cost function. Notwithstanding, optimization�]based approaches still appear computationally expensive when dealing with large arrays because of wide dimension of solution space to be sampled. In order to properly deal with these computational issues, this contribution presents an innovative approach based on an optimal excitation matching procedure. By exploiting the relationship between independently�]optimal sum and difference patterns, the dimension of the solution space is considerably reduced and efficiently sampled by taking into account the presence of array elements more suitable to change sub�]array membership. In the following, the proposed technique is described pointing out, through a representative case, its potentialities and effectiveness in dealing with large arrays. This is the author's version of the final version available at IEEE

An innovative approach based on a tree-searching algorithm for the optimal matching of independently optimum sum and difference excitations

An innovative approach for the optimal matching of independently optimum sum and difference patterns through sub-arrayed monopulse linear arrays is presented. By exploiting the relationship between the independently optimal sum and difference excitations, the set of possible solutions is considerably reduced and the synthesis problem is recast as the search of the best solution in a non-complete binary tree. Towards this end, a fast resolution algorithm that exploits the presence of elements more suitable to charge sub-array membership is presented. The results of a set of numerical experiments are reported in order to validate the proposed approach pointing out its effectiveness also in comparison with state-of-the-art optimal matching techniques. (c) 2008 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Cooperative and non-cooperative solutions to carbon leakage

A modified version of the CGE GTAP-E model is developed for assessing the economic and carbon emissions effects related to alternative policy measures implemented with the aim of reducing carbon leakage. We explore a set of scenarios, comparing solutions where Annex I countries introduce exogenously or endogenously determined carbon border taxes in order to solve the carbon leakage problem unilaterally. Results provide evidence on the scarce effectiveness of carbon tariffs in reducing carbon leakage and enhancing economic competitiveness, while they have large negative welfare effects not only on the Non-Annex countries, but also on certain Annex I countriesCarbon Leakage, Carbon Border Tax, GTAP-E model

Destruction of dimethyl ether and methyl formate by collisions with He+^+

To correctly model the abundances of interstellar complex organic molecules (iCOMS) in different environments, both formation and destruction routes should be appropriately accounted for. While several scenarios have been explored for the formation of iCOMs via grain and gas-phase processes, much less work has been devoted to understanding the relevant destruction pathways, with special reference to (dissociative) charge exchange or proton transfer reactions with abundant atomic and molecular ions such as He$^+$, H$_3^+$ and HCO$^+$. By using a combined experimental and theoretical methodology we provide new values for the rate coefficients and branching ratios (BRs) of the reactions of He$^+$ ions with two important iCOMs, namely dimethyl ether (DME) and methyl formate (MF). We also review the destruction routes of DME and MF by other two abundant ions, namely H$_3^+$ and HCO$^+$. Based on our recent laboratory measurements of cross sections and BRs for the DME/MF + He$^+$ reactions over a wide collision energy range, we extend our theoretical insights on the selectivity of the microscopic dynamics to calculate the rate coefficients $k(T)$ in the temperature range from 10 to 298 K. We implement these new and revised kinetic data in a general model of cold and warm gas, simulating environments where DME and MF have been detected. Due to stereodynamical effects present at low collision energies, the rate coefficients, BRs and temperature dependences here proposed differ substantially from those reported in KIDA and UDfA, two of the most widely used astrochemical databases. These revised rates impact the predicted abundances of DME and MF, with variations up to 40% in cold gases and physical conditions similar to those present in prestellar coresComment: accepted for publication in Astronomy and Astrophysics (manuscript no. AA/2018/34585), 10 pages, 3 figure

Using abstract interpretation to add type checking for interfaces in Java bytecode verification

AbstractJava interface types support multiple inheritance. Because of this, the standard bytecode verifier ignores them, since it is not able to model the class hierarchy as a lattice. Thus, type checks on interfaces are performed at run time. We propose a verification methodology that removes the need for run-time checks. The methodology consists of: (1) an augmented verifier that is very similar to the standard one, but is also able to check for interface types in most cases; (2) for all other cases, a set of additional simpler verifiers, each one specialized for a single interface type. We obtain these verifiers in a systematic way by using abstract interpretation techniques. Finally, we describe an implementation of the methodology and evaluate it on a large set of benchmarks