| 1. |
- Adcox, K, et al.
(författare)
-
Centrality dependence of the high (PT) charged hadron suppression in Au+Au collisions at root s(NN)=130 GeV
- 2003
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 561:1-2, s. 82-92
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Tidskriftsartikel (refereegranskat)abstract
- PHENIX has measured the centrality dependence of charged hadron p(T) spectra from Au +An collisions at root(s)NN = 130 GeV The truncated mean p(T) decreases with centrality for p(T) > 2 GeV/c, indicating an apparent reduction of the contribution from hard scattering to high p(T) hadrdn production. For central collisions the yield at high p(T) is shown to be suppressed compared to binary nucleon-nucleon collision scaling of p + p, data. This suppression is monotonically increasing with centrality, but most of the change occurs below 30% centrality, i.e., for collisions with less than similar to140 participating nucleons. The observed p(T) and centrality dependence is consistent with the particle production predicted by models including hard scattering and subsequent energy loss of the scattered partons in the dense matter created in the collisions. (C) 2003 Published by Elsevier Science B.V.
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| 2. |
- Adcox, K, et al.
(författare)
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Event-by-event fluctuations in mean p(T) and mean E(T) in root s(NN)=130 GeVAu+Au collisions
- 2002
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 66:2
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Tidskriftsartikel (refereegranskat)abstract
- Distributions of event-by-event fluctuations of the mean transverse momentum and mean transverse energy near mid-rapidity have been measured in Au+Au collisions at roots(NN)=130 GeV at the Relativistic Heavy-Ion Collider. By comparing the distributions to what is expected for statistically independent particle emission, the magnitude of nonstatistical fluctuations in mean transverse momentum is determined to be consistent with zero. Also, no significant nonrandom fluctuations in mean transverse energy are observed. By constructing a fluctuation model with two event classes that preserve the mean and variance of the semi-inclusive p(T) or e(T) spectra, we exclude a region of fluctuations in roots(NN)=130 GeV Au+Au collisions.
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| 3. |
- Adcox, K, et al.
(författare)
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Flow Measurements via Two-Particle Azimuthal Correlations in Au+Au Collisions at sqrt[sNN]=130 GeV
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 89
-
Tidskriftsartikel (refereegranskat)abstract
- Two-particle azimuthal correlation functions are presented for charged hadrons produced in Au+Au collisions at the Relativistic Heavy Ion Collider (sqrt[sNN]=130 GeV). The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values (v2) show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone ε, the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low pT. A breakdown of this ε scaling is observed for charged hadrons with pT >1.0 GeV/c.
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| 4. |
- Adcox, K, et al.
(författare)
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Measurement of Lambda and (Lambda)over-bar particles in Au plus Au collisions at root s(NN)=130 GeV
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 89:9
-
Tidskriftsartikel (refereegranskat)abstract
- We present results on the measurement of Lambda and (&ULambda;) over bar production in Au+Au collisions at roots(NN)=130 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The (&ULambda;) over bar/Lambda ratios are constant as a function of p(T) and the number of participants. The measured net Lambda density is significantly larger than predicted by models based on hadronic strings (e.g., HIJING) but in approximate agreement with models which include the gluon-junction mechanism.
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| 5. |
- Adcox, K, et al.
(författare)
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Measurement of single electrons and implications for charm production in Au+Au collisions at root(NN)-N-S=130 GeV
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 88:19
-
Tidskriftsartikel (refereegranskat)abstract
- Transverse momentum spectra of electrons from Au+Au collisions at roots(NN) = 130 GeV have been measured at midrapidity by the PHENIX experiment at the Relativistic Heavy Ion Collider. The spectra show an excess above the background from photon conversions and light hadron decays. The electron signal is consistent with that expected from semileptonic decays of charm. The yield of the electron signal dN(e)/dy for p(T) > 0.8 GeV/c is 0.025 +/- 0.004(stat) +/- 0.010( syst) in central collisions, and the corresponding charm cross section is 380 +/- 60(stat) +/- 200(syst ) mub per binary nucleon-nucleon collision.
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| 6. |
- Adcox, K, et al.
(författare)
-
Net charge fluctuations in Au+Au interactions root s(NN)=130 GeV
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 89
-
Tidskriftsartikel (refereegranskat)abstract
- Data from Au+ Au interactions at s(NN)=130 GeV, obtained with the PHENIX detector at the Relativistic Heavy-Ion Collider, are used to investigate local net charge fluctuations among particles produced near midrapidity. According to recent suggestions, such fluctuations may carry information from the quark-gluon plasma. This analysis shows that the fluctuations are dominated by a stochastic distribution of particles, but are also sensitive to other effects, like global charge conservation and resonance decays.
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| 7. |
- Adcox, K, et al.
(författare)
-
PHENIX detector overview
- 2003
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0167-5087. ; 499:2-3, s. 469-479
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Tidskriftsartikel (refereegranskat)abstract
- The PHENIX detector is designed to perform a broad study of A-A, p-A, and p-p collisions to investigate nuclear matter under extreme conditions. A wide variety of probes, sensitive to all timescales, are used to study systematic variations with species and energy as well as to measure the spin structure of the nucleon. Designing for the needs of the heavy-ion and polarized-proton programs has produced a detector with unparalleled capabilities. PHENIX measures electron and muon pairs, photons, and hadrons with excellent energy and momentum resolution. The detector consists of a large number of subsystems that are discussed in other papers in this volume. The overall design parameters of the detector are presented. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 8. |
- Adcox, K, et al.
(författare)
-
Suppression of hadrons with large transverse momentum in central Au+Au collisions at root s(NN)=130 GeV
- 2002
-
Ingår i: Physical Review Letters. - 1079-7114. ; 88:2
-
Tidskriftsartikel (refereegranskat)abstract
- Transverse momentum spectra for charged hadrons and for neutral pions in the range 1 Gev/c < P-T < 5 GeV/c have been measured by the PHENIX experiment at RHIC in Au + Au collisions at rootS(NN) = 130 GeV. At high p(T) the spectra from peripheral nuclear collisions are consistent with scaling the spectra from p + p collisions by the average number of binary nucleon-nucleon collisions. The spectra from central collisions are significantly suppressed when compared to the binary-scaled p + p expectation, and also when compared to similarly binary-scaled peripheral collisions, indicating a novel nuclear-medium effect in central nuclear collisions at RHIC energies.
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| 9. |
- Adcox, K, et al.
(författare)
-
Transverse-mass dependence of two-pion correlations in Au+Au collisions at root(NN)-N-S=130 GeV
- 2002
-
Ingår i: Physical Review Letters. - 1079-7114. ; 88:19
-
Tidskriftsartikel (refereegranskat)abstract
- Two-pion correlations in roots(NN) = 130 GeV Au+Au collisions at RHIC have been measured over a broad range of pair transverse momentum k(T) by the PHENIX experiment at RHIC. The k(T) dependent transverse radii are similar to results from heavy-ion collisions at roots(NN) = 4.1 , 4.9, and 17.3 GeV, whereas the longitudinal radius increases monotonically with beam energy. The ratio of the outwards to sidewards transverse radii (R-out/R-side) is consistent with unity and independent of k(T) .
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| 10. |
- Amnell, Tobias, et al.
(författare)
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Code Synthesis for Timed Automata
- 2002
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Ingår i: Nordic Journal of Computing. - 1236-6064. ; 9:4, s. 269-300
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Tidskriftsartikel (refereegranskat)
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| 11. |
- Amnell, Tobias, et al.
(författare)
-
Code Synthesis for Timed Automata
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a framework for development of real-time embedded systems based on the recently presented model of timed automata extended with real-time tasks. It has been shown previously that design problems such as reachability and schedulability are decidable for the model of timed automata with tasks. In this paper we describe how to automatically synthesise executable code with predictable timing behaviour, which is guaranteed to meet constraints (timing and other) imposed on the design model. To demonstrate the applicability of the framework, implemented in the Times tool, we present a case-study of a well known production cell, built in LEGO and controlled by a Hitachi H8 based LEGO Mindstorm control brick.
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| 12. |
- Cao, Jun, et al.
(författare)
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Helicobacter pylori-antigen-binding fragments expressed on the filamentous M13 phage prevent bacterial growth
- 2000
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Ingår i: Biochimica et Biophysica Acta - General Subjects. - 0304-4165 .- 1872-8006. ; 1474:1, s. 107-113
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Tidskriftsartikel (refereegranskat)abstract
- Colonization of the human stomach by Helicobacter pylori is associated with the development of gastritis, duodenal ulcer, mucosa-associated lymphoid tissue (MALT) lymphoma, and gastric cancer. H. pylori-antigen-binding single-chain variable fragments (ScFv) were derived from murine hybridomas producing monoclonal antibodies and expressed as a g3p-fusion protein on a filamentous M13 phage. The recombinant ScFv-phage reacted specifically with a 30-kDa monomeric protein of a H. pylori surface antigen preparation and by means of immunofluorescence microscopy the phage was shown to bind to both the spiral and coccoid forms of the bacterium. In vitro, the recombinant phage exhibited a bacteriocidal effect and inhibited specifically the growth of all the six strains of H. pylori tested. When H. pylori was pretreated with the phage 10 min before oral inoculation of mice, the colonization of the mouse stomachs by the bacterium was significantly reduced (P<0.01). The results suggest that genetic engineering may be used to generate therapy-effective phages.
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| 13. |
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| 14. |
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| 15. |
- Sun, Y. H., et al.
(författare)
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Theoretical studies on nonlinear optical properties of two newly synthesized compounds : PVPHC and DPVPA
- 2004
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 394:03-jan, s. 176-181
-
Tidskriftsartikel (refereegranskat)abstract
- The nonlinear optical properties of two newly synthesized molecules 9-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-9H-carbazole (PVPHC) and diphenyl-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (DPVPA) have been studied using hybrid density functional theory at B3LYP level. A few-state model, as well as response theory, have been employed to calculate their two-photon absorption cross-sections. The theoretical results are in good agreement with the experimental measurements available. It is found that the maximal two-photon absorption cross-sections of these compounds can be well described by a three-state model and both compounds have large two-photon absorption cross-section in optical regime. Strong charge-transfer process upon excitation has been revealed, indicating that these two compounds are good candidates as two-photon polymerization initiators.
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| 16. |
- Sun, Y. H., et al.
(författare)
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Two-photon absorption properties of multi-branched bis-(styryl)benzene based organic chromophores
- 2004
-
Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0166-1280. ; 682:03-jan, s. 185-189
-
Tidskriftsartikel (refereegranskat)abstract
- Two-photon absorption (TPA) cross-sections of a series of multi-branched trans-stilbene charge transfer compounds with benzene as the coupling center have been theoretically investigated using analytical response theory at the random phase approximation level. It shows that the TPA cross-sections of compounds with a quasi-one-dimensional geometrical arrangement can be enhanced through the pure electronic coupling of different branches. The effects of different combination of donor/acceptor substitutions on the TPA cross-sections have also been discussed.
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| 17. |
- Sun, Yi-Qian, 1969-
(författare)
-
Experimental Helicobacter pylori infection in an animal model
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Helicobacter pylori is a microaerophilic Gram-negative bacterium colonizing the human stomach. The prevalence of this infection is between 20-90% depending on geographic location. Comprehensive studies have shown significant relationships between H. pylori infection and chronic gastritis, peptic ulcer and gastric carcinoma. The mechanisms behind these associations are still unclear in many aspects. The objective of this thesis was to elucidate some pathogenetic aspects of H. pylori infection based on an animal model using Mongolian gerbils.Aims: To determine bacterial profiles in the stomach of gerbils with and without H. pylori infection. To study the long-term morpho-functional development of H. pylori-induced gastritis. To investigate the gastric mucosal barrier function and to explore the effects of dietary antioxidant vitamin supplements on H. pylori-associated chronic gastritis.Methods and results: Mongolian gerbils were inoculated with H. pylori ATCC 43504 or culture broth (controls). The animals were killed at scheduled time points. The gastric microflora was profiled and identified by temporal temperature gradient gel electrophoresis (TTGE), cloning and pyrosequencing of 16S rDNA variable V3 region. TTGE and pyrosequencing revealed the presence of a mixed bacterial flora in the stomach of both H. pylori infected and control animals. In both cases, lactobacilli appeared to prevail. In H. pylori-infected gerbils, serum concentrations of anti-H. pylori IgG and gastrin increased over time. Mucosal epithelial proliferation quantified after immunohistochemical labeling with 5-bromo-2'-deoxy-uridine was increased in the antrum in short-term gastritis, followed by an increase in the corpus in the long-term. Gene expression of pro-inflammatory cytokines was quantitated by real-time RT-PCR. Interleukin-1beta and tumor necrosis factor-alpha expression was increased in H. pylori-infected gerbils. Beta-actin was not a reliable endogenous control for relative quantitative RT-PCR. Histological parameters of gastritis were semiquantitatively assessed and expressed as a "gastritis score". Gastritis scores increased over time and reached a peak 32 weeks after inoculation. With time there was an expansion of gastritis from the antrum to the corpus. Severe inflammation, ulcer development and pseudopyloric metaplasia (glandular atrophy) were characteristic features. Gastric mucosal samples were mounted in Ussing chambers and 51Cr-EDTA (paracellular probe) and horseradish peroxidase (HRP, protein antigen) were used as indicators of gastric mucosal barrier function. Short-term gastritis showed increased mucosal permeability to 51Cr-EDTA in the antrum. Long-standing gastritis was associated with increased 51Cr-EDTA permeation in both the antrum and corpus and an increased HRP flux in the antrum. In the vitamin supplement study, concentrations of 3-nitrotyrosine (nitrosative protein damage) and thiobarbituric acid reactive substances (TBARS) (oxidative lipid damage) in the gastric mucosa were determined with an immunodot blot and a fluorometric method, respectively. Mucosal concentrations of carbonyl carbons on proteins (oxidative protein damage) and 8-hydroxydeoxyguanosine (oxidative DNA damage) were determined by ELISA. Vitamin supplements had no effect on the colonization with H. pylori. Vitamin C as well as vitamin E supplements reduced mucosal 3-nitrotyrosine concentrations to normal levels in the infected animals. Vitamin E supplement induced decreased mucosal protein carbonyls and TBARS in short-term gastritis. In addition, vitamin C supplement caused attenuated mucosal oxidative DNA damage and milder mucosal inflammation in short-term gastritis.Conclusions: Lactobacilli, the prevailing indigenous bacterium in the stomach of gerbils, may have a probiotic impact on the colonization of H. pylori. The long-term morpho-functional development in the stomach of H. pylori-infected Mongolian gerbils resembles that of H. pylori-infected humans. H. pylori-induced gastritis in gerbils is associated with a long-standing gastric mucosal barrier dysfunction, which follows the extension of chronic gastritis from the antrum into the corpus over time. This impaired barrier function may contribute to perpetuation of chronic inflammation and may be involved in H. pylori-associated carcinogenesis. Vitamin C as well as vitamin E supplements lead to some short-term protective effects on H. pylori-induced stritis but these effects seem to subside over time when the infection persists.
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| 18. |
- Sun, Yi-Qian, 1969-, et al.
(författare)
-
Long-standing gastric mucosal barrier dysfunction in Helicobacter pylori-induced gastritis in Mongolian gerbils
- 2004
-
Ingår i: Helicobacter. - : Wiley. - 1083-4389 .- 1523-5378. ; 9:3, s. 217-227
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Tidskriftsartikel (refereegranskat)abstract
- Background and Aims. Helicobacter pylori infection causes chronic gastritis and leads to peptic ulcer and gastric adenocarcinoma. An impaired gastric mucosal barrier could be involved in these processes. Our aim was to investigate gastric barrier function in H. pylori-induced gastritis.Methods. Stripped gastric mucosal tissues of H. pylori-infected Mongolian gerbils (4 weeks and 70 weeks after inoculation, respectively) and controls were mounted in Ussing chambers. 51Cr-EDTA (paracellular probe) and horseradish peroxidase (HRP, protein antigen) were used to assess mucosal barrier function. The electrophysiological parameters of the mucosa (transepithelial potential, short circuit current, and transepithelial resistance) were monitored as measurements of barrier integrity and viability. Tissue histology was performed to assess inflammation.Results. In the antrum, both short-term gastritis [4.68 (3.88–5.74) × 10−6 vs. control 2.86 (2.34–3.77) × 10−6 cm/s, p < .001] and gastritis of long-standing [5.72 (3.88–10.94) × 10−6 cm/s, p < .001 vs. control] showed increased permeability to 51Cr-EDTA. In long-standing antral gastritis there was also an increased HRP flux [9.01 (2.98–45.02) vs. control 0.52 (0.06–1.20) pmol/h/cm2, p < .001]. In the corpus, permeability to 51Cr-EDTA was increased only in long-standing gastritis [4.63 (3.64–7.45) × 10−6 vs. control 2.86 (2.12–3.98) × 10−6 cm/s, p < .01]. Gastric mucosal permeability to 51Cr-EDTA was correlated to histological inflammation and inflammatory activity. The levels of serum anti-H. pylori immunoglobulin G were positively correlated to HRP flux and 51Cr-EDTA permeation.Conclusions. Helicobacter pylori-induced gastritis in Mongolian gerbils was associated with a long-standing gastric mucosal barrier dysfunction. The barrier defect extended from the antrum into the corpus over time. This impaired barrier function may contribute to perpetuation of chronic inflammation and may be involved in H. pylori-associated carcinogenesis.
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| 19. |
- Sun, Yi-Qian, 1969-, et al.
(författare)
-
Profiling and identification of eubacteria in the stomach of Mongolian gerbils with and without Helicobacter pylori infection
- 2003
-
Ingår i: Helicobacter. - : Wiley. - 1083-4389 .- 1523-5378. ; 8:2, s. 149-157
-
Tidskriftsartikel (refereegranskat)abstract
- Background. Mongolian gerbils are frequently used to study Helicobacter pylori-induced gastritis and its consequences. The presence of an indigenous bacterial flora with suppressive effect on H. pylori may cause difficulties with establishing this experimental model.Aim. The aim of the present study was to determine bacterial profiles in the stomach of Mongolian gerbils with and without (controls) H. pylori infection.Methods. Gastric tissue from H. pylori ATCC 43504 and CCUG 17874 infected and control animals were subjected to microbial culturing and histology. In addition, gastric mucosal samples from H. pylori ATCC 43504 infected and control animals were analyzed for bacterial profiling by temporal temperature gradient gel electrophoresis (TTGE), cloning and pyrosequencing of 16S rDNA variable V3 region derived PCR amplicons.Results. Oral administration of H. pylori ATCC 43504, but not CCUG 17874, induced colonization and gastric inflammation in the stomach of Mongolian gerbils. Temporal temperature gradient gel electrophoresis (TTGE) and partial 16S rDNA pyrosequencing revealed the presence of DNA representing a mixed bacterial flora in the stomach of both H. pylori ATCC 43504 infected and control animals. In both cases, lactobacilli appeared to be dominant.Conclusion. These findings suggest that indigenous bacteria, particularly lactobacilli, may have an impact on the colonization and growth of H. pylori strains in the stomach of Mongolian gerbils.
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| 20. |
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| 21. |
- Sun, Yi-Ran, et al.
(författare)
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A Novel Quadrature BandpassSampling in SDR Front-Ends
- 2004
-
Ingår i: Proceeding of Biennial Analog Signal ProcessingConference, (ASP 2004). - Oxford : Oxford Brookes University.
-
Konferensbidrag (refereegranskat)abstract
- In this paper, a Generalized Quadrature BandPass Sampling (GQBPS) and inherent FIR filteringare briefly reviewed. Both theoretical analysis and simulation results show that this inherentFIR filtering not only has the advantage of image and interference rejection, but also is helpfulto suppress noise aliasing. A realizable implementation by uniform quadrature BPS (UQBPS)shows promise to sufficiently suppress the noise aliasing in BPS systems.
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| 22. |
- Sun, Yi-Ran, et al.
(författare)
-
Algorithms for Nonuniform Bandpass Sampling in Radio Receiver
- 2003
-
Ingår i: PROCEEDINGS OF THE 2003 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS, VOL I - ANALOG CIRCUITS AND SIGNAL PROCESSING. ; , s. 1-4
-
Konferensbidrag (refereegranskat)abstract
- Bandpass Sampling (BPS) technique enables one to have an interface between IF stage and ADC in a radio receiver. Nonuniform BPS has the potential to suppress aliasing without care of the information band position of a modulated signal. However, a signal cannot be reconstructed from its nonuniform samples by using only an ideal lowpass filter. In this paper, a filter is, generalized to a reconstruction algorithm (RA). Six different algorithms for reconstructing a signal from its nonuniform samples are summarized. A general reconstruction formula in terms of a basis-kernel (BK) function is used to describe the algorithms. Finally, with regard to. the application of radio communications, accuracy of reconstruction, computational complexity and hardware implementation are shown and compared for these algorithms.
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| 23. |
- Sun, Yi-Ran, et al.
(författare)
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Effects of Noise and Jitter on Algorithms for Bandpass Sampling in Radio Receiver
- 2004
-
Ingår i: 2004 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS, VOL 1, PROCEEDINGS. - 078038251X ; , s. 1761-1764
-
Konferensbidrag (refereegranskat)abstract
- BandPass Sampling (BPS) is an undersampling technique by intentional aliasing. Conventional uniform discrete sampling within an f(s) band normally results in a bad signal-to-noise ratio (SNR) due to signal spectrum aliasing. The noise combined in each of the f(s) bands below the highest frequency of the signal (the so called noise spectrum aliasing) and timing jitter are two causes of performance degradation in BPS system. Nonuniform BPS has the potential to suppress signal spectrum aliasing due to the aperiodic property of NonUniform Sampling (NUS). In this paper, the frequency spectra of Uniform Sampling (US) and NUS are analyzed, signal spectrum aliasing, noise spectrum aliasing and jitter effects in BPS are studied. Finally, the performance of reconstruction algorithms (RAs) for nonuniform BPS in the presence of sources of performance degradation are discussed based on simulations.
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| 24. |
- Sun, Yi-Ran
(författare)
-
Nonuniform bandpass sampling in radio receivers
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As an interface between radio receiver front-ends and digital signal processing blocks, sampling devices play a dominant role in digital radio communications. As an interface between radio receiver front-ends and digital signal processing blocks, sampling devices play a dominant role in digital radio communications. Based on different sampling theorems (e.g., classic Shannon’s sampling theorem, Papoulis’ Generalized sampling theorem, bandpass sampling theory), signals are processed by the sampling devices and then undergo additional processing. It is a natural goal to obtain the signals at the output of the sampling devices without loss of information. In conventional radio receivers, all the down-conversion and channel selection are realized in analog hardware. The associated sampling devices in A/D converters are based on the classic Shannon’s sampling theorem. Driven by the increased speed of microprocessors, there is a tendency to use mixed-signal/digital hardware and software to realize more functions (e.g., down-conversion, channel selection, demodulation and detection) in a radio communication system. The new evolution of radio receiver architecture is Software Defined Radio (SDR). One design goal of SDR is to put the A/D converter as close as possible to the antenna. BandPass Sampling (BPS) enables one to have an interface between the higher IF and the A/D converter by a sampling rate of 2B or more (B is the information bandwidth), and it might be a solution to SDR. A signal can be uniquely determined from the samples by NonUniform Sampling (NUS) such that NUS has the potential to suppress harmful signal spectrum aliasing. BPS makes use of the signal spectrum aliasing to represent the signal uniquely at any band position. A harmful aliasing of signal spectrum will cause a performance degradation. It is of great benefit to use NUS scheme in BPS system. However, a signal cannot be recovered from its nonuniform samples by using only an ideal lowpass filter (or the classic Shannon’s reconstruction function). The reconstruction of the samples by NUS is crucial for the implementation of NUS. Besides the harmful signal spectrum aliasing, noise aliasing and timing jitter are other two sources of performance degradation in a BPS system. Noise aliasing is the direct consequence of lower sampling rate of subsampling. With the increase of input frequency by directly sampling a signal at higher IF, the timing error of the sampling clock causes large jitter effects on the sampled-data signal. In this thesis work, first, a filter generalized by a certain Reconstruction Algorithm (RA) is proposed to reconstruct the signal from its nonuniform samples. A Based on different sampling theorems (e.g., classic Shannon’s sampling theorem, Papoulis’ Generalized sampling theorem, bandpass sampling theory), signals are processed by the sampling devices and then undergo additional processing. It is a natural goal to obtain the signals at the output of the sampling devices without loss of information. In conventional radio receivers, all the down-conversion and channel selection are realized in analog hardware. The associated sampling devices in A/D converters are based on the classic Shannon’s sampling theorem. Driven by the increased speed of microprocessors, there is a tendency to use mixed-signal/digital hardware and software to realize more functions (e.g., down-conversion, channel selection, demodulation and detection) in a radio communication system. The new evolution of radio receiver architecture is Software Defined Radio (SDR). One design goal of SDR is to put the A/D converter as close as possible to the antenna. BandPass Sampling (BPS) enables one to have an interface between the higher IF and the A/D converter by a sampling rate of 2B or more (B is the information bandwidth), and it might be a solution to SDR. A signal can be uniquely determined from the samples by NonUniform Sampling (NUS) such that NUS has the potential to suppress harmful signal spectrum aliasing. BPS makes use of the signal spectrum aliasing to represent the signal uniquely at any band position. A harmful aliasing of signal spectrum will cause a performance degradation. It is of great benefit to use NUS scheme in BPS system. However, a signal cannot be recovered from its nonuniform samples by using only an ideal lowpass filter (or the classic Shannon’s reconstruction function). The reconstruction of the samples by NUS is crucial for the implementation of NUS. Besides the harmful signal spectrum aliasing, noise aliasing and timing jitter are other two sources of performance degradation in a BPS system. Noise aliasing is the direct consequence of lower sampling rate of subsampling. With the increase of input frequency by directly sampling a signal at higher IF, the timing error of the sampling clock causes large jitter effects on the sampled-data signal. In this thesis work, first, a filter generalized by a certain Reconstruction Algorithm (RA) is proposed to reconstruct the signal from its nonuniform samples. A
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| 25. |
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