| 1. |
- Brandt, Adam R., et al.
(författare)
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Energy Intensity and Greenhouse Gas Emissions from Tight Oil Production in the Bakken Formation
- 2016
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:11, s. 9613-9621
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Tidskriftsartikel (refereegranskat)abstract
- The Bakken formation has contributed to the recent rapid increase in U.S. oil production, reaching a peak production of >1.2 × 106 barrels per day in early 2015. In this study, we estimate the energy intensity and greenhouse gas (GHG) emissions from 7271 Bakken wells drilled from 2006 to 2013. We model energy use and emissions using the Oil Production Greenhouse Gas Emissions Estimator (OPGEE) model, supplemented with an open-source drilling and fracturing model, GHGfrack. Overall well-to-refinery-gate (WTR) consumption of natural gas, diesel, and electricity represent 1.3%, 0.2%, and 0.005% of produced crude energy content, respectively. Fugitive emissions are modeled for a “typical” Bakken well using previously published results of atmospheric measurements. Flaring is a key driver of emissions: wells that flared in 2013 had a mean flaring rate that was ≈500 standard cubic feet per barrel or ≈14% of the energy content of the produced crude oil. Resulting production-weighted mean GHG emissions in 2013 were 10.2 g of CO2 equivalent GHGs per megajoule (henceforth, gCO2eq/MJ) of crude. Between-well variability gives a 5–95% range of 2–28 gCO2eq/MJ. If flaring is completely controlled, Bakken crude compares favorably to conventional U.S. crude oil, with 2013 emissions of 3.5 gCO2eq/MJ for nonflaring wells, compared to the U.S. mean of ≈8 gCO2eq/MJ.
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| 2. |
- Cai, Z., et al.
(författare)
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Amplified wintertime Barents Sea warming linked to intensified Barents oscillation
- 2022
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9318 .- 1748-9326. ; 17:4
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Tidskriftsartikel (refereegranskat)abstract
- In recent decades, the Barents Sea has warmed more than twice as fast as the rest of the Arctic in winter, but the exact causes behind this amplified warming remain unclear. In this study, we quantify the wintertime Barents Sea warming (BSW, for near-surface air temperature) with an average linear trend of 1.74 °C decade-1 and an interdecadal change around 2003 based on a surface energy budget analysis using the ERA5 reanalysis dataset from 1979-2019. Our analysis suggests that the interdecadal change in the wintertime near-surface air temperature is dominated by enhanced clear-sky downward longwave radiation (CDLW) associated with increased total column water vapor. Furthermore, it is found that a mode of atmospheric variability over the North Atlantic region known as the Barents oscillation (BO) strongly contributed to the BSW with a stepwise jump in 2003. Since 2003, the BO turned into a strengthened and positive phase, characteristic of anomalous high pressure over the North Atlantic and South of the Barents Sea, which promoted two branches of heat and moisture transport from southern Greenland along the Norwegian Sea and from the Eurasian continent to the Barents Sea. This enhanced the water vapor convergence over the Barents Sea, resulting in BSW through enhanced CDLW. Our results highlight the atmospheric circulation related to the BO as an emerging driver of the wintertime BSW through enhanced meridional atmospheric heat and moisture transport over the North Atlantic Ocean.
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| 3. |
- Cai, Z. Y., et al.
(författare)
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Interdecadal variability of the warm Arctic-cold Eurasia pattern linked to the Barents oscillation
- 2023
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Ingår i: Atmospheric Research. - : Elsevier BV. - 0169-8095. ; 287
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Tidskriftsartikel (refereegranskat)abstract
- Observed winter near-surface air temperature anomalies in the Northern Hemisphere have exhibited a warm Arctic-cold Eurasia (WACE) pattern with interdecadal variation in recent decades, but the exact mechanism behind WACE is still under debate. This study used reanalysis data and climate model simulations to investigate the interdecadal variability of the WACE pattern on a centennial scale, as well as the role of atmospheric circulations. It is found that the second mode of atmospheric variability over the North Atlantic-Arctic region, known as the Barents oscillation (BO), played a dominant role in regulating the interdecadal variability of WACE. The atmospheric circulation associated with the positive phase of the BO corresponds to an anomalous enhancement of the quasi-barotropic anticyclone near the southern Barents-Kara Seas (BKS) and the North Atlantic, as well as a weakening of the mid-latitude westerly jet. This atmospheric circulation anomaly favors the northward transport of atmospheric heat and moisture to the BKS from the mid-latitudes, resulting in an increased air temperature through downward longwave radiation. Concurrently cold air is transported from the polar region to Central Eurasia (CE), decreasing air temperature over CE. The amplified temperature anomaly dipole results in the decadal enhancement of the WACE pattern. The atmospheric circulation anomalies related to the negative phase of the BO are the opposite, which in turn leads to the decadal weakening of the WACE pattern. Our results further support the important role of internal atmospheric variability in the formation of WACE and emphasize that the atmospheric circulation associated with the BO is the main driver of WACE decadal variability over the past century.
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| 4. |
- Cao, Zhigang, 1983, et al.
(författare)
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Semi-analytical analysis of the isolation to moving-load induced ground vibrations by trenches on a poroelastic half-space
- 2012
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 331:4, s. 947-961
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Tidskriftsartikel (refereegranskat)abstract
- A semi-analytical model is proposed to investigate the screening efficiency of trenches to moving-load induced ground vibrations. The ground is modeled as a fully saturated poroelastic half-space governed by Biot's dynamic poroelastic theory. The trenches are obtained by placing three rectangular elastic layers with appropriate width upon the poroelastic half-space. By Helmholtz decomposition, the displacement fields of the elastic layers are decomposed into three scalar potentials. Analytical solutions are obtained based on Fourier transform and Fourier series in the transformed domain. The time-domain results are obtained by the fast Fourier transform (FFT). The different performances of trenches on a saturated poroelastic half-space and a single-phase elastic half-space to the moving load-induced ground vibration are identified. It is found that the discrepancy of the screening efficiencies between the two models becomes significant when the load speed approaches the Rayleigh wave speed of the ground surface. Also, some parametric studies for the screening efficiency of the trench on the poroelastic half-space are presented.
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| 5. |
- Wang, H. Y., et al.
(författare)
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Covalently Adaptable Elastin-Like Protein-Hyaluronic Acid (ELP-HA) Hybrid Hydrogels with Secondary Thermoresponsive Crosslinking for Injectable Stem Cell Delivery
- 2017
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Ingår i: Advanced Materials for Optics and Electronics. - : Wiley. - 1616-301X .- 1616-3028. ; 27:28
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Tidskriftsartikel (refereegranskat)abstract
- Shear-thinning, self-healing hydrogels are promising vehicles for therapeutic cargo delivery due to their ability to be injected using minimally invasive surgical procedures. An injectable hydrogel using a novel combination of dynamic covalent crosslinking with thermoresponsive engineered proteins is presented. Ex situ at room temperature, rapid gelation occurs through dynamic covalent hydrazone bonds by simply mixing two components: hydrazine-modified elastin-like protein (ELP) and aldehyde-modified hyaluronic acid. This hydrogel provides significant mechanical protection to encapsulated human mesenchymal stem cells during syringe needle injection and rapidly recovers after injection to retain the cells homogeneously within a 3D environment. In situ, the ELP undergoes a thermal phase transition, as confirmed by coherent anti-Stokes Raman scattering microscopy observation of dense ELP thermal aggregates. The formation of the secondary network reinforces the hydrogel and results in a tenfold slower erosion rate compared to a control hydrogel without secondary thermal crosslinking. This improved structural integrity enables cell culture for three weeks postinjection, and encapsulated cells maintain their ability to differentiate into multiple lineages, including chondrogenic, adipogenic, and osteogenic cell types. Together, these data demonstrate the promising potential of ELP-HA hydrogels for injectable stem cell transplantation and tissue regeneration.
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| 6. |
- Yeh, Sonia, 1973, et al.
(författare)
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Energy Intensity and Greenhouse Gas Emissions from Oil Production in the Eagle Ford Shale
- 2017
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 31:2, s. 1440-1449
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Tidskriftsartikel (refereegranskat)abstract
- A rapid increase in horizontal drilling and hydraulic fracturing in shale and “tight” formations that began around 2000 has resulted in record increases in oil and natural gas production in the U.S. This study examines energy consumption and greenhouse gas (GHG) emissions from crude oil and natural gas produced from ∼8,200 wells in the Eagle Ford Shale in southern Texas from 2009 to 2013. Our system boundary includes processes from primary exploration wells to the refinery entrance gate (henceforth well-to-refinery or WTR). The Eagle Ford includes four distinct production zones—black oil (BO), volatile oil (VO), condensate (C), and dry gas (G) zones—with average monthly gas-to-liquids ratios (thousand cubic feet per barrel—Mcf/bbl) varying from 0.91 in the BO zone to 13.9 in the G zone. Total energy consumed in drilling, extracting, processing, and operating an Eagle Ford well is ∼1.5% of the energy content of the produced crude and gas in the BO and VO zones, compared with 2.2% in the C and G zones. On average, the WTR GHG emissions of gasoline, diesel, and jet fuel derived from crude oil produced in the BO and VO zones in the Eagle Ford play are 4.3, 5.0, and 5.1 gCO2e/MJ, respectively. Comparing with other known conventional and unconventional crude production where upstream GHG emissions are in the range 5.9–30 gCO2e/MJ, oil production in the Eagle Ford has lower WTR GHG emissions.
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| 7. |
- Yuan, Z. H., et al.
(författare)
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Analytical solution for calculating vibrations from twin circular tunnels
- 2019
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Ingår i: Soil Dynamics and Earthquake Engineering. - : Elsevier BV. - 0267-7261. ; 117, s. 312-327
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Tidskriftsartikel (refereegranskat)abstract
- The calculation of vibrations from a single tunnel embedded in a full- or half-space due to underground moving trains has been well studied in the literature. A common assumption made in the majority of vibration prediction models is to neglect the presence of a neighboring tunnel, however, twin tunnels are a particularly preferred construction for urban underground railways with one as the inbound tunnel and the other as the outbound tunnel. The neglect of the interaction between twin tunnels may lead to inaccuracies of the calculation of vibrations from underground railways. The present paper proposes a novel analytical solution, which takes the multiple scattering effects between the two tunnels into account. The two tunnels are modelled as elastic hollow cylinders and the soil surrounding the tunnels as an elastic, homogeneous full-space containing two cylindrical cavities. The wave field in the full-space with two cavities consists of outgoing waves from each tunnel outside the two scattering surfaces while the wave field in the tunnel wall is a combination of outgoing and regular cylindrical waves. The translation of the outgoing cylindrical wave functions is required to satisfy the boundary conditions at the other tunnel. Numerical results show that there are two critical velocities for a twin tunnel in a full-space system, both of which are around the shear wave velocity of the soil. Through comparison with the single tunnel solution, the addition of a second tunnel at different separation distances and angles has a significant influence on the soil response, especially in the high frequency range, but the response at the tunnel with the source is not much affected.
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| 8. |
- Yuan, Z. H., et al.
(författare)
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Analytical wave function method for modelling a twin tunnel embedded in a saturated poroelastic full-space
- 2019
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Ingår i: Computers and Geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 114
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Tidskriftsartikel (refereegranskat)abstract
- An analytical wave function method for the calculation of vibrations from two tunnels embedded in a saturated poroelastic full-space due to a harmonic point load is given, in which the multiple scattering between twin tunnels is considered exactly. The two tunnels made of viscoelastic material are modelled as two hollow cylinders. The soil surrounding two tunnels is water-saturated, and modelled as a two-phase poroelastic material. The wave field in the full-space with two circular cavities is a superposition of outgoing waves outside the two cavity surfaces. As there is water in the soil, the hydraulic boundary at the tunnel-soil interface is necessary when solving this multi-scattering problem. The translation properties of outgoing waves are adopted to apply boundary conditions described in two sets of cylindrical coordinates. The proposed analytical method for modelling twin tunnels provides a new tool to study the interaction between twin tunnels buried in a poroelastic medium. Some typical numerical results are given to illustrate the influence of the soil permeability and the permeability of the tunnel-soil interface on the displacement and pore pressure responses. In addition, the results for a single tunnel are compared to those of a twin tunnel with various separation distances and angles.
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| 9. |
- Yuan, Z. H., et al.
(författare)
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Benchmark solution for vibrations from a moving point source in a tunnel embedded in a half-space
- 2017
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 387, s. 177-193
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Tidskriftsartikel (refereegranskat)abstract
- A closed-form semi-analytical solution for the vibrations due to a moving point load in a tunnel embedded in a half-space is given in this paper. The tunnel is modelled as an elastic hollow cylinder and the ground surrounding the tunnel as a linear viscoelastic material. The total wave field in the half-space with a cylindrical hole is represented by outgoing cylindrical waves and down-going plane waves. To apply the boundary conditions on the ground surface and at the tunnel-soil interface, the transformation properties between the plane and cylindrical wave functions are employed. The proposed solution can predict the ground vibration from an underground railway tunnel of circular cross-section with a reasonable computational effort and can serve as a benchmark solution for other computational methods. Numerical results for the ground vibrations on the free surface due to a moving constant load and a moving harmonic load applied at the tunnel invert are presented for different load velocities and excitation frequencies. It is found that Rayleigh waves play an important role in the ground vibrations from a shallow tunnel. (C) 2016 Elsevier Ltd. All rights reserved.
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| 10. |
- Yuan, Z. H., et al.
(författare)
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Closed-Form Analytical Solution for Vibrations from a Tunnel Embedded in a Saturated Poroelastic Half-Space
- 2017
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Ingår i: Journal of Engineering Mechanics - ASCE. - : American Society of Civil Engineers (ASCE). - 1943-7889 .- 0733-9399. ; 143:9, s. 04017079-
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Tidskriftsartikel (refereegranskat)abstract
- A closed-form analytical solution for ground-borne vibrations from a tunnel embedded in a saturated poroelastic half-space is proposed in this paper. The tunnel modeled as an elastic hollow cylinder is surrounded by the water-saturated poroelastic material. The total wave field in the poroelastic half-space with a cylindrical cavity consists of the outgoing cylindrical waves and the down-going plane waves. In addition to the traction-free condition on the ground surface and the continuous conditions of displacement and stress at the tunnel-soil interface, hydraulic boundary conditions on these two scattering surfaces are required to solve this multiple-scattering problem. The transformation properties between the plane and cylindrical wave functions are employed to apply the boundary conditions expressed in both the rectangular and cylindrical coordinate systems. Numerical results for the displacements of the solid on the ground surface and the pore pressure in the saturated soil attributable to a harmonic point load applied at the tunnel invert are presented. The influence of the soil permeability and the hydraulic boundary at the tunnel-soil interface on the free-field responses is investigated. The proposed solution can serve as a benchmark for other computational methods and as an efficient tool for predicting vibrations from a tunnel embedded in a saturated poroelastic half-space.
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