| 1. |
- Falconer, D., et al.
(författare)
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New Air-interface Technologies and Deployment Concepts
- 2006
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Ingår i: Technologies for the Wireless Future: Wireless World Research Forum (WWRF). - Chichester, UK : John Wiley & Sons. - 0470029056 - 9780470029053 ; , s. 131-226
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Barack, Leor, et al.
(författare)
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Black holes, gravitational waves and fundamental physics : a roadmap
- 2019
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Ingår i: Classical and quantum gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 36:14
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Forskningsöversikt (refereegranskat)abstract
- The grand challenges of contemporary fundamental physics dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'.
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| 3. |
- Bruton, Sean, et al.
(författare)
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The Impact of Cosmic Variance on Inferences of Global Neutral Fraction Derived from Lyα Luminosity Functions during Reionization
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 953:1
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the impact of field-to -field variation, deriving from cosmic variance, in measured Ly alpha emitter (LAE) luminosity functions (LFs) and this variation's impact on inferences of the neutral fraction of the intergalactic medium (IGM) during reionization. We post-process a z = 7 IGM simulation to populate the dark matter halos with LAEs. These LAEs have realistic UV magnitudes, Ly alpha fluxes, and Ly alpha line profiles. We calculate the attenuation of Ly alpha emission in universes with varying IGM neutral fraction, (x) over bar (H I). In a (x) over bar (H I) = 0.3 simulation, we perform 100 realizations of a mock 2 deg(2) survey with a redshift window Delta z = 0.5 and flux limit f(Ly alpha) > 1 x 10(-17)erg s(-1) cm(-2); such a survey is typical in depth and volume of the largest LAE surveys conducted today. For each realization, we compute the LAE LF and use it to recover the input x(H I). Comparing the inferred values of (x) over bar (H) (I) across the ensemble of the surveys, we find that cosmic variance, deriving from large-scale structure and variation in the neutral gas along the sightline, imposes a floor in the uncertainty of Delta(x) over bar (HI) similar to 0.2 when (x) over bar (H) (I) = 0.3. We explore mitigation strategies to decrease this uncertainty, such as increasing the volume, decreasing the flux limit, or probing the volume with many independent fields. Increasing the area and/or depth of the survey does not mitigate the uncertainty, but composing a survey with many independent fields is effective. This finding highlights the best strategy for LAE surveys aiming at constraining the (x) over bar (HI) of the universe during reionization.
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| 4. |
- Luo, J., et al.
(författare)
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Transmit Beamforming for Inter-Operator Spectrum Sharing : From Theory to Practice
- 2012
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Ingår i: Proceedings of the International Symposium on Wireless Communication Systems. - : IEEE conference proceedings. - 9781467307604 - 9781467307611 ; , s. 291-295
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Konferensbidrag (refereegranskat)abstract
- In this paper, four transmit beamforming (BF) techniques are selected and compared to realize inter-operator spectrum sharing, which is a promising solution for the spectrum shortage problem. The BF techniques include two game-theoretic (GT) algorithms, zero-forcing (ZF) and minimum mean square error (MMSE). After a brief description of the BF techniques in a multiple-input single-output (MISO) system, their computational complexity is analyzed. The effectiveness of these techniques in real radio frequency (RF) signal transmission is verified by implementation on a flexible hardware-in-the-loop (HIL) testbed. First, several important aspects regarding practical implementation are discussed. Afterwards, the HIL measurement results are shown, where considerable sum rate gain can be observed due to spectrum sharing. Finally, the appropriate BF technique can be chosen based on a tradeoff between complexity and performance.
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| 5. |
- Rutkowski, Michael J., et al.
(författare)
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The Lyman Continuum Escape Fraction of Emission Line-selected z similar to 2.5 Galaxies Is Less Than 15%
- 2017
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 841:2
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Tidskriftsartikel (refereegranskat)abstract
- Recent work suggests that strong emission line, star-forming galaxies (SFGs) may be significant Lyman continuum leakers. We combine archival Hubble Space Telescope broadband ultraviolet and optical imaging (F275W and F606W, respectively) with emission line catalogs derived from WFC3 IR G141 grism spectroscopy to search for escaping Lyman continuum (LyC) emission from homogeneously selected z similar to 2.5 SFGs. We detect no escaping Lyman continuum from SFGs selected on [O II] nebular emission (N = 208) and, within a narrow redshift range, on [O III]/[O II]. We measure 1 sigma upper limits to the LyC escape fraction relative to the non-ionizing UV continuum from [O II] emitters, f(esc) less than or similar to 5.6%, and strong [O III]/[O II] > 5 ELGs, f(esc) less than or similar to 14.0%. Our observations are not deep enough to detect f(esc) similar to 10% typical of low-redshift Lyman continuum emitters. However, we find that this population represents a small fraction of the star-forming galaxy population at z similar to 2. Thus, unless the number of extreme emission line galaxies grows substantially to z greater than or similar to 6, such galaxies may be insufficient for reionization. Deeper survey data in the rest-frame ionizing UV will be necessary to determine whether strong line ratios could be useful for pre-selecting LyC leakers at high redshift.
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