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- 2019
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Tidskriftsartikel (refereegranskat)
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- Aaltonen, T., et al.
(författare)
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Combination of CDF and D0 measurements of the W boson helicity in top quark decays
- 2012
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 85:7, s. 071106-
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Tidskriftsartikel (refereegranskat)abstract
- We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7-5.4 fb(-1) of p (p) over bar collisions collected during Run II of the Fermilab Tevatron collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f(0)) and right-handed (f(+)) helicities, we find f(0) = 0.722 +/- 0.081[+/- 0.062(stat) +/- 0.052(syst)] and f(+) = -0.033 +/- 0.046[+/- 0.034(stat) +/- 0.031(syst)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f(0) = 0.682 +/- 0.057[+/- 0.035(stat) +/- 0.046(syst)] for fixed f(+) and f(+) = -0.015 +/- 0.035[+/- 0.018(stat) +/- 0.030(syst)] for fixed f(0). The results are consistent with standard model expectations.
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| 5. |
- Aaltonen, T., et al.
(författare)
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Combination of Tevatron Searches for the Standard Model Higgs Boson in the W+W- Decay Mode
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:6, s. 061802-
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Tidskriftsartikel (refereegranskat)abstract
- We combine searches by the CDF and D0 Collaborations for a Higgs boson decaying to W+W-. The data correspond to an integrated total luminosity of 4.8 (CDF) and 5.4 (D0) fb(-1) of p (p) over bar collisions at root s = 1.96 TeV at the Fermilab Tevatron collider. No excess is observed above background expectation, and resulting limits on Higgs boson production exclude a standard model Higgs boson in the mass range 162-166 GeV at the 95% C.L.
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- Sun, Lian, et al.
(författare)
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Exploring the influence of reservoir impoundment on surrounding tree growth
- 2021
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Ingår i: Advances in Water Resources. - : Elsevier BV. - 0309-1708 .- 1872-9657. ; 153
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Tidskriftsartikel (refereegranskat)abstract
- At the local scale, artificial impounded reservoirs in dry regions exert influence on the surrounding local climate. Impounded reservoirs have been found to alter precipitation patterns and increase temperature, specific humidity and surface evaporation. The consequences of impoundment or its related climatic changes on the surrounding vegetation are still not well understood. We here examined the potential effect on surrounding tree growth of the impoundment of the Ertan Reservoir, China, in 1998. We measured Yunnan pine tree rings at three sites on a slope close to the reservoir and two control sites far away from the reservoir. We compared the annual radial growth of tree rings at all sites with air temperature, precipitation and air humidity in the region. We also used cumulative distribution functions to quantify the probability of attributing radial growth changes to background climate variability. We find an enhancement of tree growth from 2000 to 2002, right after the reservoir's impounding in experimental and control sites. Hence, the tree growth can initially be explained by favourable conditions benefiting tree growth. However, we cannot entirely attribute such enhancement to the background climate variability when studying the relationship between tree growth and climatic variables over the 36 years and their probability of occurrence. Tree growth in the three years following impoundment can only be attributed to the simultaneous effect of favourable regional climate conditions and the reservoir's impoundment in itself. These conditions decrease vegetation stress by decreasing air temperature and increasing air relative humidity. Although the findings of this study shed more light on the environmental and climatic changes induced by the impoundment of reservoirs, they also call for the need of monitoring climatic variables in the vicinity of reservoirs.
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| 7. |
- Das, Kaustav K., et al.
(författare)
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Probing the Low-mass End of Core-collapse Supernovae Using a Sample of Strongly-stripped Calcium-rich Type IIb Supernovae from the Zwicky Transient Facility
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 959:1
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Tidskriftsartikel (refereegranskat)abstract
- The fate of stars in the zero-age main-sequence (ZAMS) range ≈8–12 M⊙ is unclear. They could evolve to form white dwarfs or explode as electron-capture supernovae (SNe) or iron core-collapse SNe (CCSNe). Even though the initial mass function indicates that this mass range should account for over 40% of all CCSN progenitors, few have been observationally confirmed, likely due to the faintness and rapid evolution of some of these transients. In this paper, we present a sample of nine Ca-rich/O-poor Type IIb SNe detected by the Zwicky Transient Facility with progenitors likely in this mass range. These sources have a [Ca ii] λλ7291, 7324/[O i] λλ6300, 6364 flux ratio of ≳2 in their nebular spectra. Comparing the measured [O i] luminosity (≲1039 erg s−1) and derived oxygen mass (≈0.01 M⊙) with theoretical models, we infer that the progenitor ZAMS mass for these explosions is less than 12 M⊙. The ejecta properties (Mej ≲ 1 M⊙ and Ekin ∼ 1050 erg) are also consistent. The low ejecta mass of these sources indicates a class of strongly-stripped SNe that is a transition between the regular stripped-envelope SNe and ultra-stripped SNe. The progenitor could be stripped by a main-sequence companion and result in the formation of a neutron star−main sequence binary. Such binaries have been suggested to be progenitors of neutron star−white dwarf systems that could merge within a Hubble time and be detectable with LISA.
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| 8. |
- Dou, Jin-Hu, et al.
(författare)
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Atomically precise single-crystal structures of electrically conducting 2D metal-organic frameworks
- 2021
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Ingår i: Nature Materials. - : Springer Science and Business Media LLC. - 1476-1122 .- 1476-4660. ; 20, s. 222-228
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Tidskriftsartikel (refereegranskat)abstract
- Electrically conducting 2D metal-organic frameworks (MOFs) have attracted considerable interest, as their hexagonal 2D lattices mimic graphite and other 2D van der Waals stacked materials. However, understanding their intrinsic properties remains a challenge because their crystals are too small or of too poor quality for crystal structure determination. Here, we report atomically precise structures of a family of 2D pi-conjugated MOFs derived from large single crystals of sizes up to 200 mu m, allowing atomic-resolution analysis by a battery of high-resolution diffraction techniques. A designed ligand core rebalances the in-plane and out-of-plane interactions that define anisotropic crystal growth. We report two crystal structure types exhibiting analogous 2D honeycomb-like sheets but distinct packing modes and pore contents. Single-crystal electrical transport measurements distinctively demonstrate anisotropic transport normal and parallel to the pi-conjugated sheets, revealing a clear correlation between absolute conductivity and the nature of the metal cation and 2D sheet packing motif. Two-dimensional MOFs can possess porosity and electrical conductivity but are difficult to grow as single crystals. Here, by balancing in-plane and out-of-plane interactions, single crystals of sizes up to 200 mu m are grown, allowing in-plane transport measurements and atomic-resolution analysis.
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| 9. |
- Jiang, Dong-yi, et al.
(författare)
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Surface water quality and potential health risk assessments in Changsha-Zhuzhou-Xiangtan section of Xiangjiang River, China
- 2019
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Ingår i: journal of central south university. - : Springer Science and Business Media LLC. - 2095-2899 .- 2227-5223. ; 26:12, s. 3252-3260
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Tidskriftsartikel (refereegranskat)abstract
- The Changsha-Xiangtan-Zhuzhou City Group is a heavy industrial district and accepted as the serious pollution area in the Xiangjiang River basin. In this study, 7 metals (Pb, Hg, Cd, As, Zn, Cu and Se) and the river water quality parameters including pH, dissolved oxygen (DO), Escherichia coli (E. coli), potassium permanganate index (CODMn), dichromate oxidizability (CODCr), five-day biochemical oxygen demand (BOD5), ammonia nitrogen (NH4+-N), total nitrogen (TN), total phosphorus (TP) and fluoride (F-) in 18 sampling sites of the Changsha-Xiangtan-Zhuzhou section are monthly monitored in 2016, which is the year to step into the second stage of the Xiangjiang River Heavy Metal Pollution Control Implementation Plan. It is found that E. coli, TN and TP are the main pollutants in the Changsha-Zhuzhou-Xiangtan section, and the pollution of heavy metal is not serious but As with potential risk to local people especially children should be concerned. In addition, Xiangtan city is mainly featured with heavy metal pollution, while Zhuzhou and Changsha city are both featured with other pollutants from municipal domestic sewage.
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| 10. |
- Sai, Hanna, et al.
(författare)
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Observations of the very young Type Ia Supernova 2019np with early-excess emission
- 2022
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 514:3, s. 3541-3558
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Tidskriftsartikel (refereegranskat)abstract
- Early-time radiative signals from Type Ia supernovae (SNe Ia) can provide important constraints on the explosion mechanism and the progenitor system. We present observations and analysis of SN 2019np, a nearby SN Ia discovered within 1–2 days after the explosion. Follow-up observations were conducted in optical, ultraviolet, and near-infrared bands, covering the phases from ∼−16.7 d to ∼+ 367.8 d relative to its B-band peak luminosity. The photometric and spectral evolutions of SN 2019np resemble the average behaviour of normal SNe Ia. The absolute B-band peak magnitude and the post-peak decline rate are Mmax(B) = −19.52 ± 0.47 mag and Δm15(B) = 1.04 ± 0.04 mag, respectively. No Hydrogen line has been detected in the nebular-phase spectra of SN 2019np. Assuming that the 56Ni powering the light curve is centrally located, we find that the bolometric light curve of SN 2019np shows a flux excess up to 5.0 per cent in the early phase compared to the radiative diffusion model. Such an extra radiation perhaps suggests the presence of an additional energy source beyond the radioactive decay of central nickel. Comparing the observed colour evolution with that predicted by different models, such as interactions of SN ejecta with circumstellar matter (CSM)/companion star, a double-detonation explosion from a sub-Chandrasekhar mass white dwarf (WD) and surface 56Ni mixing, we propose that the nickel mixing is more favoured for SN 2019np.
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