456 research outputs found
Size-effect independence of hybrid fiber-reinforced roller-compacted concrete fracture toughness
The present paper aims to prove the size-effect independence of Hybrid Fiber-Reinforced RCC (HyFR-RCC) fracture toughness determined through the Modified Two-Parameter Model (MTPM). A micromechanical numerical model is applied to simulate the fracture behavior of seven series of single edge-notched specimens, made of both plain-RCCs and FR-RCCs (single and hybrid reinforcements), subjected to three-point bending. The MTPM is applied to the numerical load vs CMOD curves to compute the fracture toughness. A comparison with experimental values, available in the literature, is performed. Therefore, RCC specimens with different sizes are numerically simulated and the fracture toughness is analytically determined through the MTPM, proving the size-effect independence
The ATESP Radio Survey II. The Source Catalogue
This paper is part of a series reporting the results of the Australia
Telescope ESO Slice Project (ATESP) radio survey obtained at 1400 MHz with the
Australia Telescope Compact Array (ATCA) over the region covered by the ESO
Slice Project (ESP) galaxy redshift survey. The survey consists of 16 radio
mosaics with ~8"x14" resolution and uniform sensitivity (1sigma noise level ~79
microJy) over the whole area of the ESP redshift survey (~26 sq. degrees at
decl. -40 degr). Here we present the catalogue derived from the ATESP survey.
We detected 2960 distinct radio sources down to a flux density limit of ~0.5
mJy (6sigma), 1402 being sub-mJy sources. We describe in detail the procedure
followed for the source extraction and parameterization. The internal accuracy
of the source parameters was tested with Monte Carlo simulations and possible
systematic effects (e.g. bandwidth smearing) have been quantified.Comment: 14 pages, 14 Postscript figures, Accepted for publication in A&A
Suppl. Corrected typos and added Journal Referenc
A novel methodology for fatigue assessment of Ductile Cast Iron (DCI) with solidification defects
In the present research work, the fatigue strength assessment of a DCI containing solidification defects is theoretically carried out by means of a procedure implementing: (i) a defect content analysis, (ii) the varea-parameter model, and (iii) the multiaxial critical plane-based criterion by Carpinteri at al. An experimental campaign available in the literature, performed on DCI specimens under multiaxial fatigue loading, is analysed. The comparison between the obtained results and the experimental data shows a quite satisfactory agreement, highlighting the criterion accuracy
Experimental and numerical study on the fatigue behaviour of the shot-earth 772
The present research work is devoted to the mechanical, fracture and fatigue experimental characterization of the shot-earth 772, with a particular attention to its fatigue behaviour. To such an aim, an extensive experimental program has been carried out, consisting of: (i) flexural and compression tests, (ii) three-point bending fracture tests, and (iii) bending and compression cyclic tests. Moreover, a FE numerical model is employed to simulate both the above bending and compression cyclic tests, after the input data validation performed by simulating the above fracture tests. The numerical fatigue lifetimes are compared with the corresponding experimental ones for both pulsating bending and compression, highlighting the model accuracy. Finally, the contours of both the damage parameter and the reduced Young modulus are plotted showing the evolution of fatigue damage
Flexural and fracture behaviour of a cement-based material reinforced with GO nanoplates
In the present research work, the mechanical properties of a cement-based material reinforced with Graphene Oxide (GO) nanoplates are experimentally investigated. In particular, a detail experimental campaign, consisting of three-point bending tests on both unnotched and edge-notched specimens, is performed in order to determine flexural strength and fracture toughness. More precisely, the flexural strength is computed as a function of the experimental values of the peak load according to UNI EN Recommendation, whereas the fracture toughness is analytically determined according to the Modified Two-Parameter Mode
Crack path estimation in the shot-earth 772 by a discrete element method
In the present paper, the fracture behaviour of the shot-earth 772, in terms of crack path, is numerically investigated. To such an aim, a version of the lattice discrete element method is used to numerically simulate fracture toughness testing performed, on the shot-earth 772, by employing the Modified Two-Parameter model. A comparison between the numerical crack path and the experimental ones is performed, highlighting as the lattice discrete element method is able to capture the kinked crack shape, typical of quasi-brittle material
HeII emitters in the VIMOS VLT Deep Survey: PopIII star formation or peculiar stellar populations in galaxies at 2<z<4.6?
The aim of this work is to identify HeII emitters at 2<z<4.6 and to constrain
the source of the hard ionizing continuum that powers the HeII emission. We
have assembled a sample of 277 galaxies with a high quality spectroscopic
redshift at 2<z<4.6 from the VVDS survey, and we have identified 39 HeII1640A
emitters. We study their spectral properties, measuring the fluxes, equivalent
widths (EW) and FWHM for most relevant lines. About 10% of galaxies at z~3 show
HeII in emission, with rest frame equivalent widths EW0~1-7A, equally
distributed between galaxies with Lya in emission or in absorption. We find 11
high-quality HeII emitters with unresolved HeII line (FWHM_0<1200km/s), 13
high-quality emitters with broad He II emission (FWHM_0>1200km/s), 3 AGN, and
an additional 12 possible HeII emitters. The properties of the individual broad
emitters are in agreement with expectations from a W-R model. On the contrary,
the properties of the narrow emitters are not compatible with such model,
neither with predictions of gravitational cooling radiation produced by gas
accretion. Rather, we find that the EW of the narrow HeII line emitters are in
agreement with expectations for a PopIII star formation, if the episode of star
formation is continuous, and we calculate that a PopIII SFR of 0.1-10 Mo yr-1
only is enough to sustain the observed HeII flux. We conclude that narrow HeII
emitters are either powered by the ionizing flux from a stellar population rare
at z~0 but much more common at z~3, or by PopIII star formation. As proposed by
Tornatore et al. (2007), incomplete ISM mixing may leave some small pockets of
pristine gas at the periphery of galaxies from which PopIII may form, even down
to z~2 or lower. If this interpretation is correct, we measure at z~3 a SFRD in
PopIII stars of 10^6Mo yr^-1 Mpc^-3 qualitatively comparable to the value
predicted by Tornatore et al. (2007).Comment: accepted for publication in A&
Lifetime estimation for 316 stainless steel specimens by using a critical plane approach
The lifetimes of 316 stainless steel specimens are herein evaluated using the multiaxial critical plane-based criterion by Carpinteri et al. for high-cycle fatigue (HCF) loading with constant amplitude. In the present paper, the stress-based version of such a criterion is applied to assess the results of experimental tests under HCF triaxial loading, the hollow cylindrical dog-bone specimens being subjected to a quenching heat treatment. The analytical results of fatigue life and initial crack plane orientation are compared with the experimental data
Studying the evolution of large-scale structure with the VIMOS-VLT Deep Survey
The VIMOS-VLT Deep Survey (VVDS) currently offers a unique combination of
depth, angular size and number of measured galaxies among surveys of the
distant Universe: ~ 11,000 spectra over 0.5 deg2 to I_{AB}=24 (VVDS-Deep),
35,000 spectra over ~ 7 deg2 to I_{AB}=22.5 (VVDS-Wide). The current ``First
Epoch'' data from VVDS-Deep already allow investigations of galaxy clustering
and its dependence on galaxy properties to be extended to redshifts ~1.2-1.5,
in addition to measuring accurately evolution in the properties of galaxies up
to z~4. This paper concentrates on the main results obtained so far on galaxy
clustering. Overall, L* galaxies at z~ 1.5 show a correlation length r_0=3.6\pm
0.7. As a consequence, the linear galaxy bias at fixed luminosity rises over
the same range from the value b~1 measured locally, to b=1.5 +/- 0.1. The
interplay of galaxy and structure evolution in producing this observation is
discussed in some detail. Galaxy clustering is found to depend on galaxy
luminosity also at z~ 1, but luminous galaxies at this redshift show a
significantly steeper small-scale correlation function than their z=0
counterparts. Finally, red galaxies remain more clustered than blue galaxies
out to similar redshifts, with a nearly constant relative bias among the two
classes, b_{rel}~1.4, despite the rather dramatic evolution of the
color-density relation over the same redshift range.Comment: 14 pages. Extended, combined version of two invited review papers
presented at: 1) XXVIth Astrophysics Moriond Meeting: "From Dark Halos to
Light", March 2006, proc. edited by L.Tresse, S. Maurogordato and J. Tran
Thanh Van (Editions Frontieres); 2) Vulcano Workshop 2006 "Frontier Objects
in Astrophysics and Particle Physics", May 2006, proc. edited by F.
Giovannelli & G. Mannocchi, Italian Physical Society (Editrice Compositori,
Bologna
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