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11.
  • Agrell, Erik, 1965, et al. (författare)
  • Power-efficient modulation formats in coherent transmission systems
  • 2009
  • Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 27:22, s. 5115-5126
  • Tidskriftsartikel (refereegranskat)abstract
    • Coherent optical transmission systems have a four-dimensional (4-D) signal space (two quadratures in two polarizations). These four dimensions can be used to create modulation formats that have a better power efficiency (higher sensitivity) than the conventional binary phase shift keying/quadrature phase shift keying (BPSK/QPSK) signals. Several examples are given, with some emphasis on a 24-level format and an 8-level format, including descriptions of how they can be realized and expressions for their symbol and bit error probabilities. These formats are, respectively, an extension and a subset of the commonly used 16-level dual-polarization QPSK format. Sphere packing simulations in 2, 3, and 4 dimensions, up to 32 levels, are used to verify their optimality. The numerical results, as the number of levels increases, are shown to agree with lattice-theoretical results. Finally, we point out that the use of these constellations will lead to improved fundamental sensitivity limits for optical communication systems, and they may also be relevant as a way of reducing power demands and/or nonlinear influence. © 2009, IEEE. All rights reserved.
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12.
  • Agrell, Erik, 1965, et al. (författare)
  • Roadmap of optical communications
  • 2016
  • Ingår i: Journal of Optics. - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 18:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications.
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13.
  • Agrell, Erik, 1965, et al. (författare)
  • Satellite constellations: Towards the nonlinear channel capacity
  • 2012
  • Ingår i: 25th IEEE Photonics Conference, IPC 2012, Burlingame, 23 - 27 September 2012 [Invited]. - 9781457707315 ; , s. 316-317
  • Konferensbidrag (refereegranskat)abstract
    • We present a family of adaptive constellations that, in a nonlinear optical fiber channel model, has a mutual information (modulation-constrained capacity) that does not decrease with signal power.
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14.
  • Agrell, Erik, 1965, et al. (författare)
  • WDM channel capacity and its dependence on multichannel adaptation models
  • 2013
  • Ingår i: 2013 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference, OFC/NFOEC [Invited]. - 9781479904570
  • Konferensbidrag (refereegranskat)abstract
    • Optical multichannel systems are often characterized by the channel capacity of a single channel, assuming a certain adaptation behavior of the other channels. We investigate some common adaptation models, which lead to dramatically different capacities.
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17.
  • Ahlborg, Henrik, et al. (författare)
  • Prevalence of osteoporosis and incidence of hip fracture in women--secular trends over 30 years.
  • 2010
  • Ingår i: BMC Musculoskeletal Disorders. - : Springer Science and Business Media LLC. - 1471-2474. ; 11
  • Tidskriftsartikel (refereegranskat)abstract
    • BACKGROUND: The number of hip fractures during recent decades has been reported to be increasing, partly because of an increasing proportion of elderly women in the society. However, whether changes in hip fracture annual incidence in women are attributable to secular changes in the prevalence of osteoporosis is unclear. METHODS: Bone mineral density was evaluated by single-photon absorptiometry at the distal radius in 456 women aged 50 years or above and living in the same city. The measurements were obtained by the same densitometer during three separate time periods: 1970-74 (n = 106), 1987-93 (n = 175) and 1998-1999 (n = 178), and the age-adjusted prevalence of osteoporosis in these three cohorts was calculated. Additionally, all hip fractures sustained in the target population of women aged 50 years or above between 1967 and 2001 were registered, whereupon the crude and the age-adjusted annual incidence of hip fractures were calculated. RESULTS: There was no significant difference in the age-adjusted prevalence of osteoporosis when the three cohorts were compared (P = 1.00). The crude annual incidence (per 10,000 women) of hip fracture in the target population increased by 110% from 40 in 1967 to 84 in 2001. The overall trend in the crude incidence between 1967 and 2001 was increasing (1.58 per 10,000 women per year; 95 percent confidence interval, 1.17 to 1.99), whereas the age-adjusted incidence was stable over the same period (0.22 per 10,000 women per year; 95 percent confidence interval, -0.16 to 0.60). CONCLUSIONS: The increased number of hip fracture in elderly women is more likely to be attributable to demographic changes in the population than to secular increase in the prevalence of osteoporosis.
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18.
  • Ahlquist, Mårten, et al. (författare)
  • Rhodium(I) hydrogenation in water : Kinetic studies and the detection of an intermediate using C-13{H-1} PHIPNMR spectroscopy
  • 2007
  • Ingår i: Inorganica Chimica Acta. - : Elsevier BV. - 0020-1693 .- 1873-3255. ; 360:5, s. 1621-1627
  • Tidskriftsartikel (refereegranskat)abstract
    • The mechanism for hydrogenation of dimethylmaleate in water using cationic rhodium complexes with water-soluble bi-dentate phosphines has been investigated using kinetics and a novel method for the indirect detection of intermediates in catalytic hydrogenation reactions, whereby a late intermediate was detected. A mechanism is proposed involving fast, irreversible substrate binding followed by a rate-determining reaction with dihydrogen.
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19.
  • Ahmad, Tauseef, 1986, et al. (författare)
  • Methodology for Power-Aware Coherent Receiver Design
  • 2013
  • Ingår i: Optics InfoBase Conference Papers. - 2162-2701. ; , s. SPT4D.4-
  • Konferensbidrag (refereegranskat)abstract
    • We describe a methodology to design and evaluate DSP hardware for a coherent receiver. Important parameters that can be assessed include DSP power consumption and chip area.
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20.
  • Akesson, Thomas, et al. (författare)
  • Primary nonoperative treatment of moderately displaced two-part fractures of the radial head
  • 2006
  • Ingår i: Journal of Bone and Joint Surgery. American Volume. - 1535-1386. ; 88A:9, s. 1909-1914
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Moderately displaced two-fragment fractures of the radial head have been treated predominantly nonoperatively. Recently, however, open reduction and internal fixation has gradually gained interest, without clear evidence that initial nonoperative treatment leads to an unfavorable outcome. As a consequence, the purpose of the present study was to evaluate the long-term outcome after the initial nonoperative treatment of this type of fracture. Methods: Fifteen men and thirty-four women, with a mean age of forty-nine years at the time of the injury, were included in the study. All patients initially had been managed nonoperatively for a two-fragment fracture of the radial head that was displaced 2 to 5 mm and that included >= 30% of the joint surface (a Mason type-IIa fracture). Early mobilization had been used for twenty-seven patients, and cast immobilization for a mean of two weeks (range, one to four weeks) had been used for twenty-two. All patients were reevaluated with a questionnaire after a mean of nineteen years, and thirty-four also had a clinical and a radiographic evaluation. Six patients had had a delayed radial head excision because of an unsatisfactory primary outcome. Results: Forty of the forty-nine patients had no subjective complaints, eight were slightly impaired as the result of occasional elbow pain, and one had daily pain. Flexion was slightly impaired in the injured elbows as compared with the uninjured elbows (137 degrees +/- 8 degrees compared with 139 degrees +/- 7 degrees) as was extension (-3 degrees +/- 7 degrees compared with 1 degrees +/- 5 degrees) and supination (86 degrees +/- 7 degrees compared with 88 degrees +/- 4 degrees) (p < 0.05 for all comparisons). The prevalence of degenerative changes on radiographs was higher for the injured elbows than for the uninjured elbows (82% [twenty-eight of thirty-four] compared with 21% [seven of thirty-four]; p < 0.01). Conclusions: The initial nonoperative treatment of Mason type-IIa fractures of the radial head that are displaced by 2 to 5 mm is associated with a predominantly favorable outcome, especially if a delayed radial head excision is performed in the few cases in which the early outcome is unsatisfactory. Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.
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