| 1. |
- Mishchenko, Petr A., et al.
(författare)
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Chiral spin liquids with crystalline Z(2) gauge order in a three-dimensional Kitaev model
- 2020
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 101:4
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Tidskriftsartikel (refereegranskat)abstract
- Chiral spin liquids (CSLs) are time-reversal-symmetry-breaking ground states of frustrated quantum magnets that show no long-range magnetic ordering but instead exhibit topological order and fractional excitations. Their realization in simple and tractable microscopic models has, however, remained an open challenge for almost two decades until it was realized that Kitaev models on lattices with odd-length loops are natural hosts for such states, even in the absence of a time-reversal-symmetry-breaking magnetic field. Here we report on the formation of CSLs in a three-dimensional Kitaev model on a hypernonagon lattice composed of nine-site loops, which differ from their widely studied two-dimensional counterparts; namely, they exhibit a crystalline ordering of the Z(2) gauge fluxes and thereby break some of the underlying lattice symmetries. We study the formation of these unconventional CSLs via extensive quantum Monte Carlo simulations and demonstrate that they are separated from the featureless paramagnet at high temperatures by a single first-order phase transition at which both time-reversal and lattice symmetries are simultaneously broken. Using variational approaches for the ground state, we explore the effect of varying the Kitaev couplings and find at least five distinct CSL phases, all of which possess crystalline ordering of the Z(2) gauge fluxes. For some of these phases, the complementary itinerant Majorana fermions exhibit gapless band structures with topological features such as Weyl nodes or nodal lines in the bulk and Fermi arc or drumhead surface states.
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| 2. |
- Khatibi, Ali, 1982-
(författare)
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Face-Centered Cubic (Al1-xCrx)2O3 Thin Films : Deposition, Characterization, and Heat Treatment Studies
- 2011
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Face centered cubic (Al1-xCrx)2O3 solid solution films, with x in the range 0.602 discharge at a substrate temperature of 500 °C. The films have a strong <100> preferred orientation. The unit cell parameter is 4.04 Å determined by x-ray diffraction and high resolution transmission electron microscopy techniques. The (Al1-xCrx)2O3 films are suggested to have a non-stoichiometric NaCl structure with 33% vacancy occupancy on Al/Cr sites. Nanoindentation shows that the films exhibit hardness values up to 26 GPa and reduced modulus of 220-235 GPa. In the present work, ex-situ annealing studies were performed on as-deposited samples for a series of temperatures up to 1100 °C and annealing time of 2,4,6,8, and 10 hours. The fcc structure remains intact up to 950 °C. A gradual phase transformation from fcc to corundum at 925 °C is observed, where annealing for 2 h yields a partial transformation and annealing for >6 h results in complete transformation to a-(Al1-xCrx)2O3. There is no indication of any phase separation into a-Cr2O3 and Al2O3.
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| 3. |
- Rodríguez, Juanjo
(författare)
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Mercury methylation in boreal aquatic ecosystems under oxic conditions and climate change : a review
- 2023
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Ingår i: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 10
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Forskningsöversikt (refereegranskat)abstract
- Methylmercury (MeHg) formation is a concerning environmental issue described in waters and sediments from multiple aquatic ecosystems. The genetic and metabolic bases of mercury (Hg) methylation have been well described in anoxic environments, but a number of factors seem to point towards alternative pathways potentially occurring in pelagic waters under oxic conditions. Boreal aquatic ecosystems are predicted to undergo increasing concentrations of dissolved organic matter (DOM) as a result of higher terrestrial runoff induced by climate change, which may have important implications in the formation of MeHg in the water column. In this review, different Hg methylation mechanisms postulated in the literature are discussed, with particular focus on potential pathways independent of the hgcAB gene pair and occurring under oxic conditions. Potential effects of DOM on Hg methylation and MeHg bioaccumulation are examined in the context of climate in boreal aquatic ecosystems. Furthermore, the implementation of meta-omic technologies and standardized methods into field measurements and incubation experiments is discussed as a valuable tool to determine taxonomic and functional aspects of Hg methylation in oxic waters and under climate change-induced conditions.
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| 4. |
- Miao, Guowang, et al.
(författare)
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Energy Efficiency in the Wideband Regime
- 2013
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Ingår i: IEEE Transactions on Wireless Communications. - : IEEE conference proceedings. - 1536-1276 .- 1558-2248. ; 12:8, s. 4102-4109
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Tidskriftsartikel (refereegranskat)abstract
- End-to-end communication is the fundamental building block of communication networks. In this paper, we discuss globally optimal energy efficient design for end-to-end communications. An end-to-end multiple-hop system with one sender, one receiver, and multiple relays is considered. We first study in detail energy-efficient designs in the wideband regime that is characterized by wide signal bandwidth and low spectral efficiency, and later briefly those in the narrowband regime. We will reveal the globally optimal link adaptation as well as relay deployment strategies such that the whole system can achieve the highest energy efficiency. The technologies proposed can be used in various communication systems, such as the deployment and communication of wired core networks and wireless relay networks, to improve their energy efficiency. While this paper focuses on a linear end-to-end network topology, the methodology can be easily extended to two-dimensional network topologies for energy-efficient designs of the whole network
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| 5. |
- Miao, Guowang
(författare)
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Energy-Efficient Uplink Multi-User MIMO
- 2013
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Ingår i: IEEE Transactions on Wireless Communications. - : IEEE Communications Society. - 1536-1276 .- 1558-2248. ; 12:5, s. 2302-2313
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses optimal energy-efficient design for uplink (UL) MU-MIMO in a single cell environment. The energy efficiency is measured by throughput per Joule, while both RF transmission power and device electronic circuit power are considered. We define the energy efficiency (EE) capacity for UL MU-MIMO and study the power allocation that achieves this capacity. First we assume all users consume a fixed amount of circuit power and show that user antennas should be used only when the corresponding spatial channels are sufficiently good and using them improves the overall network EE. Mobile devices may have improved circuit management capability and turn off circuit operations when some antennas are not used to reduce circuit power consumption. Therefore we further study energy-efficient UL MU-MIMO with improved circuit management and show that some antennas should not be used even when their channel states are good because turning them on consumes too much circuit power. Based on theoretical analysis, we further develop low-complexity yet globally optimal energy-efficient power allocation algorithms that converge to the optimum exponentially. Simulation results are provided to demonstrate the significant gain in network energy efficiency.
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| 6. |
- Miao, Guowang
(författare)
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Energy-Efficient Uplink Multi-User MIMO with Dynamic Antenna Management
- 2012
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Ingår i: 2012 IEEE Global Communications Conference (Globecom). - : IEEE. - 9781467309219 ; , s. 3437-3442
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Konferensbidrag (refereegranskat)abstract
- Energy efficiency is important for mobile devices because battery technology development has not kept up with the growing demand of ubiquitous broadband communications. This paper addresses optimal energy-efficient design for uplink (UL) MU-MIMO in a single cell environment. We assume mobile devices have dynamic antenna management capability and can turn off circuit operations when some antennas are not used to save power. We show that some antennas should not be used even when their channel states are good because turning them on consumes too much circuit power. This indicates a single antenna system could perform better than a multi-antenna system in terms of energy efficiency. Based on theoretical analysis, we further develop low-complexity yet globally optimal algorithms that converge to the optimum exponentially.
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| 7. |
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| 8. |
- Aad, G., et al.
(författare)
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- 2012
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swepub:Mat__t (refereegranskat)
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