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- Bansal, Tarun, et al.
(author)
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Suction measurement in freezing soils using pore pressure transducers
- 2021
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In: 18th Nordic Geotechnical Meeting 18-19 January 2021, Helsinki, Finland. - : Institute of Physics (IOP).
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Conference paper (peer-reviewed)abstract
- Frost heave is major problem for infrastructures build in cold regions. Frost heave occurs due to suction (negative pore water pressure) generated due to the freezing process close to the frost line, i.e., at the frozen fringe. To understand and predict these negative pore water pressures is a key factor to accurately calculate the segregation heave, i.e. heave related to the formation of ice lenses. Segregation heave is the major part of the total heave and also the most challenging to predict. Many attempts have been presented in literature where the generated suction during freezing is related to temperatures, temperature gradients, grain size of the freezing soil etc. Very few laboratory tests have been presented in which the actual suction is measured during the ice lens formation process and compared with theoretical estimations. One reason is that these measurements are challenging. This paper presents results from laboratory measurements of generated suction during freezing. Laboratory tests were conducted on a silty soil sample and suction was measured at the frozen fringe using small pore pressure transducers (PPT's). The samples were subjected to one-dimensional freezing from top to bottom in an open water system at a constant temperature gradient. Temperatures were measured at various points along the height of the soil sample while suction was measured at middle of the sample. Test results have shown that PPTs do not show pressure change in long-term static pressure test under sub-freezing temperature. For suction measurement at the frozen fringe, pore pressure readings should be measured at various points along the sample height.
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- Garmabaki, Amir H. Soleimani, et al.
(author)
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A Survey on Underground Pipelines and Railway Infrastructure at Cross-Sections
- 2019
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In: Proceedings of the 29th European Safety and Reliability Conference (ESREL 2019). - Singapore : Research Publishing Services. ; , s. 1094-1101
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Conference paper (peer-reviewed)abstract
- Underground pipelines are an essential part of the transportation infrastructure. The structural deterioration of pipelines crossing railways and their subsequent failures are critical for society and industry resulting in direct and indirect costs for all the related stakeholders. Pipeline failures are complex processes, which are affected by many factors, both static (e.g., pipe material, size, age, and soil type) and dynamic (e.g., traffic load, pressure zone changes, and environmental impacts). These failures have serious impacts on public due to safety, disruption of traffic, inconvenience to society, environmental impacts and shortage of resources. Therefore, continuous and accurate condition assessment is critical for the effective management and maintenance of pipeline networks within transportation infrastructure. The aim of this study is to identify failure modes and consequences related to the crossing of pipelines in railway corridors. Expert opinion have been collected through two set of questionnaires which have been distributed to the 291 municipalities in the whole Sweden. The failure analysis revealed that pipe deformation has higher impact followed by pipe rupture at cross-section with railway infrastructure. For underground pipeline under railway infrastructure, aging and external load gets higher ranks among different potential failure causes to the pipeline.
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- Khosropanah, Pourya, 1971, et al.
(author)
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Analysis of NbN Hot Electron Bolometer Receiver Noise Temperatures Above 2 THz With a Quantum Noise Model
- 2009
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In: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 19:3, s. 274-277
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Journal article (peer-reviewed)abstract
- This paper summarizes our receiver noise temperature data of NbN HEB mixers obtained at a number of local oscillator frequencies between 1.9 to 4.3 THz in order to verify the role of quantum noise. The experimental data show that the receiver noise temperature increases roughly linearly with frequency. At 4.3 THz, we measured a receiver noise temperature of 1300 K, which is about 6 times (hf/k B) . The noise data at different frequencies are compared to a prediction of a noise model including the contribution of quantum noise and making use of a hot-spot model for mixing. We draw a preliminary conclusion that at 4.3 THz roughly 30% of the receiver noise temperature can be ascribed to the quantum noise. However, more dedicated measurements are required in order to further support the quantum noise model for HEB mixers.
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| 9. |
- Knutsson, Sven, 1948-, et al.
(author)
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Tjäle och tjälforskning vid Luleå tekniska universitet
- 2024
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In: Bygg & teknik. - : Byggteknikförlaget. - 0281-658X .- 2002-8350. ; :1
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Journal article (other academic/artistic)abstract
- Tjäldjup, tjällyftningar och tjällossningsproblem är årligen återkommande fenomen, som inträffar när jordmaterial fryser och tinar. I Sverige är frysningen säsongsmässig, med relativt korta vintrar i söder och upp till sex månader långa i norra Sverige. Tjällossningen sker under våren och avslutas i norra Sverige först vid midsommartid och är inte sällan förknippad med att vägars bärförmåga kan påverkas negativt. Tjäldjupet ökar successivt under vintern med mer eller mindre ojämn tjällyftning som följd. Graden av tjällyftning beror av temperatur i uteluft, jordmaterial och tillgång på vatten. Just ojämnhet i tjällyftningar för vägar och järnvägar är ett problem då det påverkar såväl komfort som säkerhet. Ojämna tjällyftningar behandlas för närvarande i tre olika doktorandprojekt vid LTU och dessa beskrivs här.
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| 10. |
- Kollberg, Erik, 1937, et al.
(author)
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Quantum noise contribution to NbN hot electron bolometer receiver
- 2009
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In: Proceedings of the 20th International Symposium on Space Terahertz Technology, Charlottesville, 20-22 April 2009. ; , s. 155-
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Conference paper (peer-reviewed)abstract
- Abstract— Superconducting NbN hot electron bolometer (HEB) mixers are so far the most sensitive detectors forheterodyne spectroscopy in the frequency range between 1.5 THz and 5 THz. To reach the ultimate receiver noisetemperatures in the high end of the THz range (3-6 THz), it is crucial to understand their fundamental noise contributionfrom different origins. With increasing frequency, the classical output noise contribution should remain unchanged, butthe quantum noise contribution is expected to play an increasing role [1].This paper reports the first dedicated experiment using a single NbN HEB mixer at a number of local oscillatorfrequencies between 1.6 to 4.3 THz to address and quantify the contribution of the quantum noise to the receiver noisetemperature.We used a spiral antenna coupled NbN HEB mixer with a bolometer size of 2 μm×0.2 μm. In order to minimizeuncertainties in the corrections of the optical losses, we use a vacuum hot/cold load setup [2] to eliminate the air loss, andan uncoated elliptical Si lens. Although other components, a 3 μm Mylar beam splitter and a QMC heat filter, alsointroduce frequency dependent optical losses, they can be accurately calibrated. Furthermore, to reduce uncertainties inthe data, we measure Y-factors responding to the hot/cold load by fixing the voltage, but varying the LO power [2]. AsLO, we use a FIR gas laser.We measure the Y-factor at the optimal point at different frequencies by only varying LO frequencies, but keepingthe rest exactly the same. We obtain DSB receiver noise temperatures, which are 842 K (at 1.6 THz), 845 K (1.9 THz), 974K (2.5 THz) and 1372 K (4.3 THz). After the correction for the losses of the QMC filter and the beam splitter, the noisedata show a linear increase with increasing frequency.Using a quantum noise model [1] for HEB mixers and using a criterion for which the classical output noise must beconstant at different frequencies, we analyze the results and find the excess quantum noise factor β to be around 2 andthat 24 % of the total receiver noise temperature at 4.3 THz (at the input of the entire receiver) can be ascribed toquantum noise. Clearly the quantum noise has a small but measurable effect on the receiver noise temperature at thisfrequency.We are still analyzing different alternatives of interpretation for the mismatch loss between the bolometer andthe spiral antenna.[1] E. L. Kollberg and K. S. Yngvesson, “Quantum-noise theory for terahertz hot electron bolometer mixers,” IEEE Trans.Microwave Theory and Techniques, 54, 2077, 2006.[2] P. Khosropanah, J.R. Gao, W.M. Laauwen, M. Hajenius and T.M. Klapwijk, “Low noise NbN hot-electron bolometer mixerat 4.3 THz,” Appl. Phys. Lett., 91, 221111, 2007.
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