| 1. |
- Barnes, W. L., et al.
(författare)
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Solid-state single photon sources : light collection strategies
- 2002
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Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 18:2, s. 197-210
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Tidskriftsartikel (refereegranskat)abstract
- We examine the problem of efficiently collecting the photons produced by solid-state single photon sources. The extent of the problem is first established with the aid of simple physical concepts. Several approaches to improving the collection efficiency are then examined and are broadly categorized into two types. First are those based on cavity quantum dynamics, in which the pathways by which the source may emit a photon are restricted, thus channeling emission into one desired mode. Second are those where we try to reshape the free space modes into a target mode in an optimal way, by means of refraction, without fundamentally altering the way in which the source emits. Respectively, we examine a variety of microcavities and solid immersion lenses. Whilst we find that the micropillar microcavities offer the highest collection efficiency (similar to70%), choosing this approach may not always be appropriate due to other constraints. Details of the different approaches, their merits and drawbacks are discussed in detail.
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| 2. |
- Davis, Andrew M, et al.
(författare)
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Application and limitations of X-ray crystallographic data in structure-based ligand and drug design.
- 2003
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Ingår i: Angew Chem Int Ed Engl. - 0570-0833. ; 42:24, s. 2718-36
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Forskningsöversikt (populärvet., debatt m.m.)abstract
- Structure-based design usually focuses upon the optimization of ligand affinity. However, successful drug design also requires the optimization of many other properties. The primary source of structural information for protein-ligand complexes is X-ray crystallography. The uncertainties introduced during the derivation of an atomic model from the experimentally observed electron density data are not always appreciated. Uncertainties in the atomic model can have significant consequences when this model is subsequently used as the basis of manual design, docking, scoring, and virtual screening efforts. Docking and scoring algorithms are currently imperfect. A good correlation between observed and calculated binding affinities is usually only observed only when very large ranges of affinity are considered. Errors in the correlation often exceed the range of affinities commonly encountered during lead optimization. Some structure-based design approaches now involve screening libraries by using technologies based on NMR spectroscopy and X-ray crystallography to discover small polar templates, which are used for further optimization. Such compounds are defined as leadlike and are also sought by more traditional high-throughput screening technologies. Structure-based design and HTS technologies show important complementarity and a degree of convergence.
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| 3. |
- Robert-Philip, I., et al.
(författare)
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Generation of non-classical light by single quantum dots
- 2003
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Ingår i: Journal of Luminescence. - 0022-2313. ; 102-103:SPEC, s. 67-71
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Konferensbidrag (refereegranskat)abstract
- The emission statistics of single semiconductor quantum dots is investigated in view of generating quantum states of light. Correlation experiments show that the emission of a quantum dot can be regulated so as to produce only one photon at a time as well as correlated photon pairs. This observation opens the way to the use of semiconductor quantum dots as triggered sources of single photons, which could find applications in quantum cryptography. We then discuss the potentiality of quantum dots for the production of mutually coherent single photons as well as entangled photons that could be used in quantum information processing schemes. © 2002 Elsevier Science B.V. All rights reserved.
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| 4. |
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| 5. |
- Gallart, M., et al.
(författare)
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Single photon emission from individual semiconductor nanostructures
- 2003
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Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - 1386-9477. ; 17:1-4, s. 568-571
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Konferensbidrag (refereegranskat)abstract
- The correlation between the photons emitted by an optically pumped single quantum dot is investigated. The correlation function on a single dot isolated in a mesa shows that only one photon is emitted at a time at the exciton frequency. These quantum states of light can be generated with a high quantum efficiency, with the use of cavity effects: surrounding the dot by a pillar microcavity not only increases significantly the single photon flux but also allows the preparation of single photons all in the same quantum state (same spatial mode and same polarization). © 2002 Published by Elsevier Science B.V.
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| 6. |
- Janssen, Gerard J. M., et al.
(författare)
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Antenna Diversity for a Narrow-band successive-Cancellation Multiuser Detector
- 2004
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Ingår i: IEEE Transactions on Vehicular Technology. - New York : IEEE. - 0018-9545 .- 1939-9359. ; 53:5, s. 1303-1315
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a successive-cancellation multiuser detector (SC-MUD) for narrow-band signals operating in the Rayleigh-fading channel is shown to deteriorate severely unless very large power margins at the receiver are maintained. To mitigate this deterioration, antenna diversity is applied and adapted to the SC-MUD. In each detection stage, the best signal for detection and the corresponding combining weights are determined jointly. Two criteria for selecting the best signal based on maximizing the signal-to-noise-plus-interference ratio and maximizing the minimum distance-to-noise ratio, respectively, are proposed and evaluated. For signal combining, zero forcing and minimum mean square error (mmse) combining are considered. The obtained results show that the SC-MUD with mmse combining performs close to maximum likelihood joint detection while keeping a much lower computational complexity when the number of users is less than the number of receive antennas. The effect of channel-estimation errors is investigated for orthogonal training sequences and shown to result in a minor degradation compared to perfect estimation.
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| 7. |
- Janssen, Gerard J. M., et al.
(författare)
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BER results for a narrowband multi-user receiver based on successive substraction for MPSK modulated signals
- 2000
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Konferensbidrag (refereegranskat)abstract
- A narrowband multiuser receiver based on successive signal detection and subtraction, is proposed. The Bit Error Rate (BER) performance for M-PSK modulated signals is evaluated and analytical approximations for the BER of the individual signals are presented and compared to the actual BER. The effect of inaccurately estimated signal parameters due to noise is analyzed. BER results are presented for synchronous signals for both Additive White Gaussian Noise (AWGN) and Rayleigh fading channels.
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| 8. |
- Janssen, Gerard J. M., et al.
(författare)
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Capacity of a Cellular Radio System Using a Narrowband Multiuser Detector
- 2002
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Konferensbidrag (refereegranskat)abstract
- With a narrowband multiuser detector (MUD), multiple users can simultaneously share the same chan- nel without using a bandwidth expanding signature code when suficient power differences at the receiver are main- tained. In this paper we assess the capacity gain that can be achieved in a hypothetical cellular system with centralized power control, using a narrowband MUD based on succes- sive cancellation. The power control algorithm is adapted to multiple users per channel in a cell. Simulation results are presented for two heuristic CIR based channel assign- ment schemes. The MUD allows for a substantial capacity gain due to a tighter packing of users in a channel. The observed gain compared to a conventional single user per channel system, ranges from 1.4 to 5 for cluster sizes C = 1 and 7, respectively.
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| 9. |
- Janssen, Gerard J. M., et al.
(författare)
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Power Control and Stepwise Removal Algorithms for a Narrowband Multiuser Detector in a Cellular System
- 2002
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Ingår i: 2002 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-5, CONFERENCE PROCEEDINGS. - New York : IEEE. - 0780374002 ; , s. 345-350
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Konferensbidrag (refereegranskat)abstract
- With a narrowband multiuser detector (MUD), multiple users can simultaneously share the same channel without using a bandwidth expanding signature code when sufficient power differences at the receiver are maintained. In this paper, we estimate the capacity that can be achieved in a hypothetical cellular system with centralized power control, using a narrowband MUD based on successive cancellation. The power control algorithm is adapted to multiple users per channel in a cell.Capacity results from simulations based on user removal are presented for three removal algorithms. It is shown that the narrowband MUD has a significant potential for capacity gain due to a tighter packing of users in a channel.
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| 10. |
- Janssen, Gerard J. M., et al.
(författare)
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Symbol error probability analysis of a multiuser detector for M-PSK signals based on successive Cancellation
- 2002
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Ingår i: IEEE Journal on Selected Areas in Communications. - New York : IEEE. - 0733-8716 .- 1558-0008. ; 20:2, s. 330-338
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Tidskriftsartikel (refereegranskat)abstract
- A narrow-band multiuser receiver based on successive signal detection and subtraction, is considered in this paper. The symbol error probability (SEP) for M-PSK modulated signals is evaluated and analytical approximations for the SEP of the individual signals are presented and compared with results obtained from simulations. For geometrically related signal amplitudes, a constant minimum distance can be guaranteed independent of the number of signals. The required amplitude ratio is shown to be related to and the number of co-channel signals. Optimizing the transmitted power for the different signals while ensuring the same SEP is then addressed and closed-form expressions of the signal amplitude ratios are derived. The effect of inaccurately estimated signal parameters due to noise is also analyzed. SEP results are presented for synchronous signals in an additive white Gaussian noise environment.
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