New planetary and EB candidates from Campaigns 1-6 of the K2 mission

With only two functional reaction wheels, Kepler cannot maintain stable pointing at its original target field and entered a new mode of observation called K2. Our method is based on many years of experience in planet hunting for the CoRoT mission. Due to the unstable pointing, K2 light curves present systematics that are correlated with the target position in the CCD. Therefore, our pipeline also includes a decorrelation of this systematic noise. Our pipeline is optimised for bright stars for which spectroscopic follow-up is possible. We achieve a maximum precision on 6 hours of 6 ppm. The decorrelated light curves are searched for transits with an adapted version of the CoRoT alarm pipeline. We present 172 planetary candidates and 327 eclipsing binary candidates from campaigns 1, 2, 3, 4, 5 and 6 of K2. Both the planetary candidates and eclipsing binary candidates lists are made public to promote follow-up studies. The light curves will also be available to the community.Comment: 22 pages. 5 figures, 4 tables, Accepted for publication in A&

Study of Phase Reconstruction Techniques applied to Smith-Purcell Radiation Measurements

Measurements of coherent radiation at accelerators typically give the absolute value of the beam profile Fourier transform but not its phase. Phase reconstruction techniques such as Hilbert transform or Kramers Kronig reconstruction are used to recover such phase. We report a study of the performances of these methods and how to optimize the reconstructed profiles.Comment: Presented at IPAC'14 - THPME08

A New Hybrid Methodology According to NSM CFRP Technique for the Flexural Strengthening of RC Beams

The objective of this paper is to propose a new hybrid methodology according to near surface mounted (NSM) technique, using carbon fiber reinforced polymer (CFRP) reinforcement for the flexural strengthening of reinforced concrete (RC) beams. This NSM hybrid flexural strengthening technique combines non-prestressed and prestressed CFRP laminates in the same application in order to provide a good balance in terms of load carrying and ultimate displacement capacity to the strengthened elements. An experimental program composed of six RC beams was carried out to assess the benefits of this NSM hybrid technique when compared to the use of non-prestressed or prestressed NSM CFRP laminates (NSM prestressing technique). For this purpose, the performance of both techniques in terms of crack width, prevailing failure mode, ultimate displacement capacity, energy absorption, and load carrying capacity of the strengthened beams was assessed. The experimental tests were also simulated by executing advanced 3D nonlinear finite element analysis. Moreover, the potentialities of other configurations for the NSM hybrid technique by adopting different non-prestressed CFRP reinforcement ratios were numerically assessed executing a parametric study, and the relevant results are presented and discussed.The study reported in this paper is part of the project "PreLami - Performance of reinforced concrete structures strengthened in flexural with an innovative system using prestressed NSM CFRP laminates", with the reference PTDC/ECM/114945/2009 supported by FCT. The authors would also like to acknowledge the support provided by CLEVER Reinforcement Iberica Company, for supplying the adhesives and the laminates, and Casais and CiviTest for the preparation of the beams

Embedded Through-Section shear strengthening technique using steel and CFRP bars in RC beams of different percentage of existing stirrups

The Embedded Through-Section (ETS) technique is a promising technique for the shear strengthening of existing (RC) elements. According to this technique, holes are drilled through the beam section, and bars of steel or FRP material are introduced into these holes and bonded to the concrete with adhesive materials. An experimental program was carried out with RC T-cross section beams strengthened in shear using the ETS steel bars and ETS CFRP rods. The research is focused on the evaluation of the ETS efficiency on beams with different percentage of existing internal transverse reinforcement (ρsw=0.0%, ρsw=0.1% and ρsw=0.17%). The effectiveness of different ETS strengthening configurations was also investigated. The good bond between the strengthening ETS bars and the surrounding concrete allowed the yield initiation of the ETS steel bars and the attainment of high tensile strains in the ETS CFPR rods, leading to significant increase of shear capacity, whose level was strongly influenced by the inclination of the ETS bars and the percentage of internal transverse reinforcement.The authors wish to acknowledge Elletipi S.r.l. (Ferrara, Italy) for supporting the experimental program, Interbau S.r.l. (Milano, Italy) for applying the ETS strengthening system, BASF company Italy for providing the CFRP rods and the ENDIF Geomatic Group (University of Ferrara, Italy) for monitoring the experimental program, as well as the support provided by FCT (PTDC/ECM/114511/2009). The authors wish also acknowledge the Engineering Department of the University of Ferrara for its financial support

Assessment of the effectiveness of prestressed NSM CFRP laminates for the flexural strengthening of RC beams

The flexural behavior of RC beams strengthened with prestressed near-surface-mounted (NSM) carbon-fiber-reinforced-polymer (CFRP) laminate was investigated in this paper. For this purpose, four RC beams were tested under monotonic four-point loading. One beam was kept un-strengthened, as a control beam, and another one was strengthened with a non-prestressed NSM CFRP laminate. The remaining beams were strengthened with NSM CFRP laminates prestressed at 20% and 40% of its ultimate tensile strength. The prestressed NSM CFRP laminate technique provided a significant increment of the load carrying capacity for deflection levels corresponding to serviceability and ultimate limit states. A numerical strategy was also employed to simulate the flexural behavior of the tested RC beams. The experimental and numerical researches are described and the relevant results are presented and discussed.Fundação para a Ciência e a Tecnologia (FCT

Evaluation of the performance of full-scale RC beams prestressed with NSM-CFRP laminates

Carbon Fibre Reinforced Polymers (CFRP) applied according to the Near Surface Mounted (NSM) technique are known as capable of increasing the ultimate flexural resistance of Reinforced Concrete (RC) elements, but for Serviceability Limit States (SLS) the load increment it provides is, in general, relatively limited. Recently, researchers are giving attention towards the possibility of applying prestressed NSM-CFRPs to increase significantly the load carrying capacity of RC elements at SLS. As it is common knowledge, introducing prestress in a RC element produces an initial stress distribution, whose primary effect is, in the case of RC beams, the development of an initial deflection, typically in the opposite direction of loading. This initial stress field is the key factor that triggers most of the benefits of this technology, such as the delay in crack initiation and in steel yielding initiation. In this paper, the results of an experimental program consisting of a series of full-scale RC beams flexurally strengthened with NSM prestressed CFRP laminates up to four different levels (20%, 30%, 40% and 50%) will be presented. The experimental program is described and the main results are presented and discussed.Fundação para a Ciência e a Tecnologia (FCT

Influence of prestress level on NSM CFRP laminates for the flexural strengthening of RC beams

This study presents an experimental program to evaluate the influence of the prestressing technique on the flexural behavior of reinforced-concrete (RC) beams strengthened with near-surface-mounted (NSM) carbon-fiber-reinforced-polymer (CFRP) laminates. The experimental program was organized to highlight the benefits of this technique for flexural strengthening of RC beams with low reinforcement ratio, susceptible of not respecting serviceability-limit-state (SLS) conditions, namely the deflection limit. For this purpose, five RC beams were fabricated to be tested under monotonic four-point loading. One beam was kept unstrengthened as a control beam, and another one was strengthened with a non-prestressed NSM CFRP laminate. The remaining beams were reinforced with a NSM CFRP laminate prestressed at 20%, 30% and 40% of its nominal tensile strength. Based on the results, applying the prestress force provided an increase of load carrying capacity corresponding to the concrete cracking and steel yielding initiations compared to the non-prestressed strengthened beam. Moreover, the influence of prestress level on the prevailing failure mode of the tested beams was assessed, and the relevant results are presented and discussed. An advanced numerical strategy was also developed to simulate the tested beams, which was demonstrated capable of being used for the design of this type of structures.Fundação para a Ciência e a Tecnologia (FCT

RC beams strengthened in shear using the Embedded Through-Section technique: experimental results and analytical formulation

The Embedded Through-Section (ETS) is a recent strengthening technique that has been developed to retrofit existing reinforced concrete (RC) elements with shear reinforcement deficiencies. This technique is based on the execution of holes drilled through the element cross section, in which steel or fiber reinforced polymer (FRP) bars are inserted and bonded to the surrounding concrete with an epoxy adhesive. An experimental program was carried out with RC T-cross section beams strengthened in shear using steel ETS bars. The influence of the inclination and shear strengthening ratio of ETS on the shear strengthening efficiency was evaluated, as well as the interaction of ETS bars with existing steel stirrups. Two different analytical models are presented in this paper in order to calculate the contribution of ETS to shear resistance. The first model follows an empirical approach (experimental-based approach), while the second model takes into account the physical and mechanical principles of the technique (mechanical-based approach). The predictive performance of both models is assessed by using the experimental results.The authors wish to acknowledge the support provided by the CutInov project QREN n. 38780 supported by ADI, and by the Engineering Department of the University of Ferrara

Distinguishing the albedo of exoplanets from stellar activity

Light curves show the flux variation from the target star and its orbiting planets as a function of time. In addition to the transit features created by the planets, the flux also includes the reflected light component of each planet, which depends on the planetary albedo. This signal is typically referred to as phase curve and could be easily identified if there were no additional noise. As well as instrumental noise, stellar activity, such as spots, can create a modulation in the data, which may be very difficult to distinguish from the planetary signal. We analyze the limitations imposed by the stellar activity on the detection of the planetary albedo, considering the limitations imposed by the predicted level of instrumental noise and the short duration of the observations planned in the context of the CHEOPS mission. As initial condition, we have assumed that each star is characterized by just one orbiting planet. We built mock light curves that included a realistic stellar activity pattern, the reflected light component of the planet and an instrumental noise level, which we have chosen to be at the same level as predicted for CHEOPS. We then fit these light curves to try to recover the reflected light component, assuming the activity patterns can be modeled with a Gaussian process.We estimate that at least one full stellar rotation is necessary to obtain a reliable detection of the planetary albedo. This result is independent of the level of noise, but it depends on the limitation of the Gaussian process to describe the stellar activity when the light curve time-span is shorter than the stellar rotation. Finally, in presence of typical CHEOPS gaps in the simulations, we confirm that it is still possible to obtain a reliable albedo.Comment: Accepted for publication in A&A, 14 pages, 12 figure

Shear deformation and failure modes of the GFRP reinforced concrete beams without stirrups

The various shear-transfer actions due to: aggregate interlock effect, dowel action of the flexural reinforcement, the uncracked concrete in the compressive zone and the direct strut action for the point load close to the support, may provide different crack pattern in the shear span of the concrete beams without stirrups. The aim of this paper is to investigate the shear failure mechanisms in T-shape, single span and simply supported beams exclusively reinforced with longitudinal glass fiber reinforced polymer (GFRP) bars. The research of concrete beams flexurally reinforced with GFRP bars without stirrups indicated the possibility of occurring, besides the conventional shear-compression failure mode, another type of failure governed by the loss of bond between the ordinary reinforcement and concrete. Usually the critical shear crack in RC beams without stirrups develops through the theoretical compression strut preventing a direct transfer of the shear force to the support. The main parameter affecting the crack pattern and the shear strength of the beams is the shear span to depth ratio. However, the test results presented in this paper showed the formation of an arching effect due to the bond losing between the GFRP flexural reinforcement and concrete. This failure mode revealed unexpected critical crack pattern and failure mode. Digital image correlation (DIC) technique was used to better capture and analyse the cracking process up to the formation of the shear failure crac