5,680 research outputs found
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
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