| 1. |
- Ghorbani, Fereshte Mohammad, et al.
(author)
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Effect of hydroxyapatite nano-particles on morphology, rheology and thermal behavior of poly(Caprolactone)/chitosan blends
- 2016
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In: Materials science & engineering. C, biomimetic materials, sensors and systems. - : Elsevier. - 0928-4931 .- 1873-0191. ; 59, s. 980-989
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Journal article (peer-reviewed)abstract
- The effect of hydroxyapatite nano-particles (nHA) on morphology, and rheological and thermal properties of PCL/chitosan blends was investigated. The tendency of nHA to reside in the submicron-dispersed chitosan phase is determined using SEM and AFM images. The presence of electrostatic interaction between amide sites of chitosan and ionic groups on the nHA surface was proved by FTIR. It is shown that the chitosan phase is thermodynamically more favorable for the nano-particles to reside than the PCL phase. Lack of implementation of Cox-Merz theory for this system shows that the polymer-nano-particle network is destructed by the flow. Results from dynamic rheological measurements and Zeiler fractional model show that the presence of nHA increases the shear moduli and relaxation time of the PCL/chitosan blends. DSC measurements showed that nHA nano-particles are responsible for the increase in melting and crystallization characteristics of the PCL/chitosan blends. Based on thermogravimetric analysis, the PCL/chitosan/nHA nano-composites exhibited a greater thermal stability compared to the nHA-free blends.
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| 2. |
- Leander, John, 1976-, et al.
(author)
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Fatigue reliability assessment of welded bridge details using probabilistic fracture mechanics
- 2016
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In: IABSE Congress Stockholm 2016 Report. - Zürich : IABSE c/o ETH Hönggerberg. ; , s. 238-245
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Conference paper (peer-reviewed)abstract
- The safe life method for the fatigue life prediction of steel bridges has for several cases been shown to render misleading results. To improve the accuracy, a probabilistic model based on linear elastic fracture mechanics (LEFM) is suggested. The model is used for a sensitivity analysis on the influence of different modelling options pertinent for a fatigue assessment of bridge details. The influence of material parameters and the crack growth threshold have been investigated. The analyses have been performed for a bridge detail frequently occurring in old steel bridges and a stress range spectrum based on measurements. The results show a significant difference in the estimated fatigue life depending on the modelling options. Furthermore, the omission sensitivity factors have been estimated for the probabilistic model showing the influence of the uncertainties of the variables and which of them that needs to be determined with care.
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| 3. |
- Leclercq, Floriane, et al.
(author)
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The MUSE &ITHubble&IT Ultra Deep Field Survey VIII. Extended Lyman-alpha haloes around high-&ITz&IT star-forming galaxies
- 2017
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 608
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Journal article (peer-reviewed)abstract
- We report the detection of extended Ly alpha haloes around 145 individual star-forming galaxies at redshifts 3 <= z <= 6 in the Hubble Ultra Deep Field observed with the Multi-Unit Spectroscopic Explorer (MUSE) at ESO-VLT. Our sample consists of continuum-faint (-15 >= M-UV >= -22) Ly alpha emitters (LAEs). Using a 2D, two-component (continuum-like and halo) decomposition of Ly alpha emission assuming circular exponential distributions, we measure scale lengths and luminosities of Ly alpha haloes. We find that 80% of our objects having reliable Ly alpha halo measurements show Ly alpha emission that is significantly more extended than the UV continuum detected by HST (by a factor approximate to 4 to >20). The median exponential scale length of the Ly alpha haloes in our sample is approximate to 4.5 kpc with a few haloes exceeding 10 kpc. By comparing the maximal detected extent of the Ly alpha emission with the predicted dark matter halo virial radii of simulated galaxies, we show that the detected Ly alpha emission of our selected sample of Ly alpha emitters probes a significant portion of the cold circum-galactic medium of these galaxies (>50% in average). This result therefore shows that there must be significant HI reservoirs in the circum-galactic medium and reinforces the idea that Ly alpha haloes are ubiquitous around high-redshift Ly alpha emitting galaxies. Our characterization of the Ly alpha haloes indicates that the majority of the Ly alpha flux comes from the halo (approximate to 65%) and that their scale lengths seem to be linked to the UV properties of the galaxies (sizes and magnitudes). We do not observe a significant Ly alpha halo size evolution with redshift, although our sample for z > 5 is very small. We also explore the diversity of the Ly alpha line profiles in our sample and we find that the Ly alpha lines cover a large range of full width at half maximum (FWHM) from 118 to 512 km s(-1). While the FWHM does not seem to be correlated to the Ly alpha scale length, most compact Ly alpha haloes and those that are not detected with high significance tend to have narrower Ly alpha profiles (<350 km s(-1)). Finally, we investigate the origin of the extended Ly alpha emission but we conclude that our data do not allow us to disentangle the possible processes, i.e. scattering from star-forming regions, fluorescence, cooling radiation from cold gas accretion, and emission from satellite galaxies.
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| 4. |
- Nilsson, Peter, 1982, et al.
(author)
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Steel-Sandwich Elements in Bridge Applications
- 2015
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Reports (other academic/artistic)abstract
- Sandwich structures have been used in different applications for 100 years, since World War One. Steel sandwich elements have been proposed to be produced using an adhesive connection or discrete point spot welding. Recent increased use of and confidence in laser welding methods enables a continuous connection between the core and the face plate of a steel sandwich element. This yields a connection, and furthermore a plate element, with high strength and toughness.The high stiffness to weight ratio and the decreased level of orthotropy in comparison to conventional stiffened steel plates, is very attractive for bridge applications. Furthermore, they have a high capacity with respect to global buckling. These properties makes sandwich plate element applicable to different bridge types, as a slab in an open cross section for short and medium span bridges or in closed box section for the stiffening girder of a cable supported bridge.This report review’s the state of art regarding steel sandwich elements in bridge applications, with a focus on the corrugated core geometrical configuration. The aim of this report is to identify the gaps of knowledge regarding corrugated core steel sandwich elements for bridge applications.
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| 5. |
- Shams Hakimi, Poja, 1988, et al.
(author)
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Experimental study of transverse attachment joints with 40 and 60 mm thick main plates, improved by high-frequency mechanical impact treatment (HFMI)
- 2018
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In: Engineering structures. - : ELSEVIER SCI LTD. - 0141-0296 .- 1873-7323. ; 155, s. 251-266
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Journal article (peer-reviewed)abstract
- In recent years, high-frequency mechanical impact (HFMI) treatment has grown in popularity due to its efficiency in improving the fatigue strength of welded joints. The fatigue performance of HFMI-treated welded steel joints has, however, not been thoroughly studied for plate thicknesses above 30 mm. In this study, 40 and 60 mm thick main plates with non-load-carrying transverse attachments have been fatigue tested under constant amplitude four-point bending, both in as-welded and HFMI-treated condition to investigate the fatigue performance for large plate thicknesses, typical for weldments in bridges. Axial fatigue strengths were estimated by a modification of the experimental results with fracture mechanics calculations. The main conclusions are that HFMI treatment can result in significant fatigue strength improvement even for large main plate thicknesses and that the difference in fatigue strength between bending and axial loading is negligible for the specimen geometries used in this study.
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| 6. |
- Trujillo, Ignacio, et al.
(author)
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Introducing the LBT Imaging of Galactic Halos and Tidal Structures (LIGHTS) survey A preview of the low surface brightness Universe to be unveiled by LSST
- 2021
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 654
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Journal article (peer-reviewed)abstract
- We present the first results of the LBT Imaging of Galaxy Haloes and Tidal Structures (LIGHTS) survey. LIGHTS is an ongoing observational campaign with the 2 × 8.4 m Large Binocular Telescope (LBT) aiming to explore the stellar haloes and the low surface brightness population of satellites down to a depth of μV ∼ 31 mag arcsec−2 (3σ in 10″ × 10″ boxes) of nearby galaxies. We simultaneously collected deep imaging in the g and r Sloan filters using the Large Binocular Cameras. The resulting images are 60 times (i.e. ∼4.5 mag) deeper than those from the Sloan Digital Sky Survey, and they have characteristics comparable (in depth and spatial resolution) to the ones expected from the future Legacy Survey of Space and Time (LSST). Here we show the first results of our pilot programme targeting NGC 1042 (an M 33 analogue at a distance of 13.5 Mpc) and its surroundings. The depth of the images allowed us to detect an asymmetric stellar halo in the outskirts of this galaxy whose mass (1.4 ± 0.4 × 108 M⊙) is in agreement with the ΛCDM expectations. Additionally, we show that deep imaging from the LBT reveals low mass satellites (a few times 105 M⊙) with very faint central surface brightness μV(0) ∼ 27 mag arcsec−2 (i.e. similar to Local Group dwarf spheroidals, such as Andromeda XIV or Sextans, but at distances well beyond the local volume). The depth and spatial resolution provided by the LIGHTS survey open up a unique opportunity to explore the ‘missing satellites’ problem in a large variety of galaxies beyond our Local Group down to masses where the difference between the theory and observation (if any) should be significant.
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| 7. |
- Zamiri Akhlaghi, Farshid, 1975, et al.
(author)
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Advanced Assessment of Welded Bridges for Fatigue and Brittle Fracture
- 2018
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Reports (other academic/artistic)abstract
- Around 50% of steel and steel—concrete composite bridges owned by Trafikverket have been built before 1970, when there was limited knowledge about fatigue and brittle fracture of structural steel products. This was the case in particular for the usage of these products in construction of welded bridges. At the same time, fatigue deterioration in these structures is undergoing due to the escalation of freight volume as well as the increased axle loads of modern trains and lorries. Realistic assessment of residual service life of these structures is crucial in more efficient planning of repairs and avoiding unnecessary replacement costs. Therefore, more accurate condition assessment methods are important from both economic and sustainability aspects. While the improved assessment methods for existing structures have been subject of extensive research since 1990's, their use in regular engineering practice is still limited. This study is an attempt to review the recent advances in structural assessment of welded steel bridges and to present them in a structured manner for the use of practicing engineer. In this report, a multi-step assessment methodology for fatigue and brittle fracture of welded bridges is presented, mainly based on the past research in Europe. The assessment steps are comprised of preliminary assessment (phase I), detailed investigation (phase II), and expert investigation (part III). Detailed information is given in the report for the corresponding input data (resistance-side and action-side) and modelling options for each of these assessment steps. As expected, the more advanced method is used, the more extensive set of input data and analytical effort is required. When applicable, the assessment method has been adapted to the relevant technical requirements stipulated by Trafikverket. Finally, the application of the presented multi-step assessment is examined on a case study bridge (Göta river bridge). Phase II assessment of the bridge based on historical loading data shows insufficient fatigue life for a critical detail that has been replicated in many locations over the bridge. The results of phase III assessment suggest that intensified inspections of vulnerable details in regular time intervals are sufficient for ensuring the safe service of the structure until the end of its planned service life.
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