| 1. |
- Elsik, Christine G., et al.
(författare)
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The Genome Sequence of Taurine Cattle : A Window to Ruminant Biology and Evolution
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 324:5926, s. 522-528
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Tidskriftsartikel (refereegranskat)abstract
- To understand the biology and evolution of ruminants, the cattle genome was sequenced to about sevenfold coverage. The cattle genome contains a minimum of 22,000 genes, with a core set of 14,345 orthologs shared among seven mammalian species of which 1217 are absent or undetected in noneutherian (marsupial or monotreme) genomes. Cattle-specific evolutionary breakpoint regions in chromosomes have a higher density of segmental duplications, enrichment of repetitive elements, and species-specific variations in genes associated with lactation and immune responsiveness. Genes involved in metabolism are generally highly conserved, although five metabolic genes are deleted or extensively diverged from their human orthologs. The cattle genome sequence thus provides a resource for understanding mammalian evolution and accelerating livestock genetic improvement for milk and meat production.
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| 2. |
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| 3. |
- Sodergren, Erica, et al.
(författare)
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The genome of the sea urchin Strongylocentrotus purpuratus.
- 2006
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 314:5801, s. 941-52
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Tidskriftsartikel (refereegranskat)abstract
- We report the sequence and analysis of the 814-megabase genome of the sea urchin Strongylocentrotus purpuratus, a model for developmental and systems biology. The sequencing strategy combined whole-genome shotgun and bacterial artificial chromosome (BAC) sequences. This use of BAC clones, aided by a pooling strategy, overcame difficulties associated with high heterozygosity of the genome. The genome encodes about 23,300 genes, including many previously thought to be vertebrate innovations or known only outside the deuterostomes. This echinoderm genome provides an evolutionary outgroup for the chordates and yields insights into the evolution of deuterostomes.
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| 4. |
- Wild, W., et al.
(författare)
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Millimetron—a large Russian-European submillimeter space observatory
- 2009
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Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 23:1, s. 221-244
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Tidskriftsartikel (refereegranskat)abstract
- Millimetron is a Russian-led 12 m diameter submillimeter and far-infrared space observatory which is included in the Space Plan of the Russian Federation for launch around 2017. With its large collecting area and state-of-the-art receivers, it will enable unique science and allow at least one order of magnitude improvement with respect to the Herschel Space Observatory. Millimetron will be operated in two basic observing modes: as a single-dish observatory, and as an element of a ground-space very long baseline interferometry (VLBI) system. As single-dish, angular resolutions on the order of 3 to 12 arc sec will be achieved and spectral resolutions of up to a million employing heterodyne techniques. As VLBI antenna, the chosen elliptical orbit will provide extremely large VLBI baselines (beyond 300,000 km) resulting in micro-arc second angular resolution.
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| 5. |
- Güsten, R., et al.
(författare)
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APEX - The Atacama Pathfinder Experiment
- 2006
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6267 I
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Konferensbidrag (refereegranskat)abstract
- APEX, the Atacama Pathfinder Experiment, has been successfully commissioned and is in operation now. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the world's outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of 17-18 μm makes APEX suitable for observations up to 200 μm, through all atmospheric submm windows accessible from the ground.
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| 6. |
- Chang, Yu-mei, et al.
(författare)
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A pooled analysis of Melanocytic nevus phenotype and the risk of cutaneous melanoma at different latitudes
- 2009
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Ingår i: International Journal of Cancer. - : Wiley. - 0020-7136 .- 1097-0215. ; 124:2, s. 420-428
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Tidskriftsartikel (refereegranskat)abstract
- An abnormal nevus phenotype is associated with an increased risk of melanoma. We report a pooled analysis conducted using individual nevus data from 15 case-control studies (5,421 melanoma cases and 6,966 controls). The aims were to quantify the risk better and to determine whether relative risk is varied by latitude. Bayesian unconditional logistic random coefficients models were employed to study the risk associated with nevus characteristics. Participants with whole body nevus counts in the highest of 4 population-based categories had a greatly increased risk of melanoma compared with those in the lowest category (pooled odds ratio (pOR) 6.9 (95% confidence interval (CI): 4.4, 1.1.2) for those aged <50 years and pOR 5.1 (95% CI: 3.6, 7.5) for those aged >= 50). The pOR for presence compared with absence of any clinically atypical nevi was 4.0 (95 % CI: 2.8, 5.8). The pORs for 1-2 and >= 3 large nevi on the body compared with none were 2.9 (95% CI: 1.9, 4.3) and 7.1 (95% CI: 4.7, 11.6), respectively. The relative heterogeneities among studies were small for most measures of nevus phenotype, except for the analysis of nevus counts on the arms, which may have been due to methodological differences among studies. The pooled analysis also suggested that an abnormal nevus phenotype is associated most with melanomas on intermittently sun-exposed sites. The presence of increased numbers of nevi, large nevi and clinically atypical nevi on the body are robust risk factors for melanoma showing little variation in relative risk among studies performed at different latitudes. (C) 2008 Wiley-Liss, Inc.
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| 7. |
- Chang, Yu-mei, et al.
(författare)
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Sun exposure and melanoma risk at different latitudes: a pooled analysis of 5700 cases and 7216 controls
- 2009
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Ingår i: International Journal of Epidemiology. - : Oxford University Press (OUP). - 1464-3685 .- 0300-5771. ; 38:3, s. 814-830
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Tidskriftsartikel (refereegranskat)abstract
- Background Melanoma risk is related to sun exposure; we have investigated risk variation by tumour site and latitude. Methods We performed a pooled analysis of 15 case-control studies (5700 melanoma cases and 7216 controls), correlating patterns of sun exposure, sunburn and solar keratoses (three studies) with melanoma risk. Pooled odds ratios (pORs) and 95% Bayesian confidence intervals (CIs) were estimated using Bayesian unconditional polytomous logistic random-coefficients models. Results Recreational sun exposure was a risk factor for melanoma on the trunk (pOR 1.7; 95% CI: 1.4-2.2) and limbs (pOR 1.4; 95% CI: 1.1-1.7), but not head and neck (pOR 1.1; 95% CI: 0.8-1.4), across latitudes. Occupational sun exposure was associated with risk of melanoma on the head and neck at low latitudes (pOR 1.7; 95% CI: 1.0-3.0). Total sun exposure was associated with increased risk of melanoma on the limbs at low latitudes (pOR 1.5; 95% CI: 1.0-2.2), but not at other body sites or other latitudes. The pORs for sunburn in childhood were 1.5 (95% CI: 1.3-1.7), 1.5 (95% CI: 1.3-1.7) and 1.4 (95% CI: 1.1-1.7) for melanoma on the trunk, limbs, and head and neck, respectively, showing little variation across latitudes. The presence of head and neck solar keratoses was associated with increased risk of melanoma on the head and neck (pOR 4.0; 95% CI: 1.7-9.1) and limbs (pOR 4.0; 95% CI: 1.9-8.4). Conclusion Melanoma risk at different body sites is associated with different amounts and patterns of sun exposure. Recreational sun exposure and sunburn are strong predictors of melanoma at all latitudes, whereas measures of occupational and total sun exposure appear to predict melanoma predominately at low latitudes. Keywords Melanoma, recreational sun exposure, occupational sun exposure, total sun exposure, sunburn, solar keratoses
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| 8. |
- Richards, Stephen, et al.
(författare)
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The genome of the model beetle and pest Tribolium castaneum.
- 2008
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Ingår i: Nature. - 1476-4687. ; 452:7190, s. 949-55
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Tidskriftsartikel (refereegranskat)abstract
- Tribolium castaneum is a representative of earth’s most numerous eukaryotic order, a powerful model organism for the study of generalized insect development, and also an important pest of stored agricultural products. We describe its genome sequence here. This omnivorous beetle has evolved an ability to interact with a diverse chemical environment as evidenced by large expansions in odorant and gustatory receptors, as well as p450 and other detoxification enzymes. Developmental patterns in Tribolium are more representative of other arthropods than those found in Drosophila, a fact represented in gene content and function. For one, Tribolium has retained more ancestral genes involved in cell-cell communication than Drosophila, and some are expressed in the growth zone crucial for axial elongation in short germ development. Systemic RNAi in T. castaneum appears to use mechanisms distinct from those found in C. elegans, but nevertheless offers similar power for the elucidation of gene function and identification of targets for selective insect control.
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| 9. |
- Cornwell, William K., et al.
(författare)
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Plant species traits are the predominant control on litter decomposition rates within biomes worldwide
- 2008
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 11:10, s. 1065-1071
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Tidskriftsartikel (refereegranskat)abstract
- Worldwide decomposition rates depend both on climate and the legacy of plant functional traits as litter quality. To quantify the degree to which functional differentiation among species affects their litter decomposition rates, we brought together leaf trait and litter mass loss data for 818 species from 66 decomposition experiments on six continents. We show that: (i) the magnitude of species-driven differences is much larger than previously thought and greater than climate-driven variation; (ii) the decomposability of a species' litter is consistently correlated with that species' ecological strategy within different ecosystems globally, representing a new connection between whole plant carbon strategy and biogeochemical cycling. This connection between plant strategies and decomposability is crucial for both understanding vegetation-soil feedbacks, and for improving forecasts of the global carbon cycle.
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| 10. |
- Tomlins, Scott A., et al.
(författare)
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The role of SPINK1 in ETS rearrangement-negative prostate cancers
- 2008
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Ingår i: Cancer Cell. - Amsterdam : Elsevier. - 1535-6108 .- 1878-3686. ; 13:6, s. 519-28
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Tidskriftsartikel (refereegranskat)abstract
- ETS gene fusions have been characterized in a majority of prostate cancers; however, the key molecular alterations in ETS-negative cancers are unclear. Here we used an outlier meta-analysis (meta-COPA) to identify SPINK1 outlier expression exclusively in a subset of ETS rearrangement-negative cancers ( approximately 10% of total cases). We validated the mutual exclusivity of SPINK1 expression and ETS fusion status, demonstrated that SPINK1 outlier expression can be detected noninvasively in urine, and observed that SPINK1 outlier expression is an independent predictor of biochemical recurrence after resection. We identified the aggressive 22RV1 cell line as a SPINK1 outlier expression model and demonstrate that SPINK1 knockdown in 22RV1 attenuates invasion, suggesting a functional role in ETS rearrangement-negative prostate cancers.
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| 11. |
- Gongora, Jaime, et al.
(författare)
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Indo-European and Asian origins for Chilean and Pacific chickens revealed by mtDNA
- 2008
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 105:30, s. 10308-10313
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Tidskriftsartikel (refereegranskat)abstract
- European chickens were introduced into the American continents by the Spanish after their arrival in the 15th century. However, there is ongoing debate as to the presence of pre-Columbian chickens among Amerindians in South America, particularly in relation to Chilean breeds such as the Araucana and Passion Fowl. To understand the origin of these populations, we have generated partial mitochondrial DNA control region sequences from 41 native Chilean specimens and compared them with a previously generated database of approximate to 1,000 domestic chicken sequences from across the world as well as published Chilean and Polynesian ancient DNA sequences. The modern Chilean sequences cluster closely with haplotypes predominantly distributed among European, Indian subcontinental, and Southeast Asian chickens, consistent with a European genetic origin. A published, apparently pre-Columbian, Chilean specimen and six pre-European Polynesian specimens also cluster with the same European/Indian subcontinental/Southeast Asian sequences, providing no support for a Polynesian introduction of chickens to South America. In contrast, sequences from two archaeological sites on Easter Island group with an uncommon haplogroup from Indonesia, Japan, and China and may represent a genetic signature of an early Polynesian dispersal. Modeling of the potential marine carbon contribution to the Chilean archaeological specimen casts further doubt on claims for pre-Columbian chickens, and definitive proof will require further analyses of ancient DNA sequences and radiocarbon and stable isotope data from archaeological excavations within both Chile and Polynesia.
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| 12. |
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| 13. |
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| 14. |
- Bausch, Birke, et al.
(författare)
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Germline NF1 mutational spectra and loss-of-heterozygosity analyses in patients with pheochromocytoma and neurofibromatosis type 1.
- 2007
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Ingår i: Journal of Clinical Endocrinology and Metabolism. - : The Endocrine Society. - 0021-972X .- 1945-7197. ; 92:7, s. 2784-92
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Neurofibromatosis type 1 (NF1) is a pheochromocytoma-associated syndrome. Because of the low prevalence of pheochromocytoma in NF1, we ascertained subjects by pheochromocytoma that also had NF1 in the hope of describing the germline NF1 mutational spectra of NF1-related pheochromocytoma.MATERIALS AND METHODS: An international registry for NF1-pheochromocytomas was established. Mutation scanning was performed using denaturing HPLC for intragenic variation and quantitative PCR for large deletions. Loss-of-heterozygosity analysis using markers in and around NF1 was performed.RESULTS: There were 37 eligible subjects (ages 14-70 yr). Of 21 patients with corresponding tumor available, 67% showed somatic loss of the nonmutated allele at the NF1 locus vs. 0 of 12 sporadic tumors (P = 0.0002). Overall, 86% of the 37 patients had exonic or splice site mutations, 14% large deletions or duplications; 79% of the mutations are novel. The cysteine-serine rich domain (CSR) was affected in 35% but the RAS GTPase activating protein domain (RGD) in only 13%. There did not appear to be an association between any clinical features, particularly pheochromocytoma presentation and severity, and NF1 mutation genotype.CONCLUSIONS: The germline NF1 mutational spectra comprise intragenic mutations and deletions in individuals with pheochromocytoma and NF1. NF1 mutations tended to cluster in the CSR over the RAS-GAP domain, suggesting that CSR plays a more prominent role in individuals with NF1-pheochromocytoma than in NF1 individuals without this tumor. Loss-of-heterozygosity of NF1 markers in NF1-related pheochromocytoma was significantly more frequent than in sporadic pheochromocytoma, providing further molecular evidence that pheochromocytoma is a true component of NF1.
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| 15. |
- Bjartell, Anders, et al.
(författare)
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Association of cysteine-rich secretory protein 3 and beta-microseminoprotein with outcome after radical prostatectomy
- 2007
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Ingår i: Clinical Cancer Research. - 1078-0432. ; 13:14, s. 4130-4138
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: It has been suggested that cysteine-rich secretory protein 3 (CRISP-3) and p-microseminoprotein (MSP) are associated with outcome in prostate cancer. We investigated whether these markers are related to biochemical recurrence and whether addition of the markers improves prediction of recurring disease. Experimental Design: Tissue microarrays of radical prostatectomy specimens were analyzed for CRISP-3 and MSP by immunohistochemistry. Associations between marker positivity and postprostatectomy biochemical recurrence [prostate-specific antigen (PSA) > 0.2 ng/mL with a confirmatory level] were evaluated by univariate and multivariable Cox proportional hazards regression. Multivariable analyses controlled for preoperative PSA and pathologic stage and grade. Results: Among 945 patients, 224 had recurrence. Median follow-up for survivors was 6.0 years. Patients positive for CRISP-3 had smaller recurrence-free probabilities, whereas MSP-positive patients had larger recurrence-free probabilities. On univariate analysis, the hazard ratio for patients positive versus negative for CRISP-3 was 1.53 (P =0.010) and for MSP was 0.63 (P = 0.004). On multivariable analysis, both CRISP-3 (P = 0.007) and MSP (P = 0.002) were associated with recurrence. The hazard ratio among CRISP-3-positive/MSP-negative patients compared with CRISP-3-negative/MSP-positive patients was 2.38. Adding CRISP-3 to a base model that included PSA and pathologic stage and grade did not enhance the prediction of recurrence, but adding MSP increased the concordance index minimally from 0.778 to 0.781. Conclusion: We report evidence that CRISP-3 and MSP are independent predictors of recurrence after radical prostatectomy for localized prostate cancer. However, addition of the markers does not importantly improve the performance of existing predictive models. Further research should aim to elucidate the functions of CRISP-3 and MSP in prostate cancer cells.
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| 16. |
- Borgström, Johannes
(författare)
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Equivalences and Calculi for Formal Verification of Cryptographic Protocols
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Security protocols are essential to the proper functioning of any distributed system running over an insecure network but often have flaws that can be exploited even without breaking the cryptography. Formal cryptography, the assumption that the cryptographic primitives are flawless, facilitates the construction of formal models and verification tools. Such models are often based on process calculi, small formal languages for modelling communicating systems. The spi calculus, a process calculus for the modelling and formal verification of cryptographic protocols, is an extension of the pi calculus with cryptography. In the spi calculus, security properties can be formulated as equations on process terms, so no external formalism is needed. Moreover, the contextual nature of observational process equivalences takes into account any attacker/environment that can be expressed in the calculus. We set out to address the problem of automatic verification of observational equivalence in an extension of the spi calculus: A channel-passing calculus with a more general expression language. As a first step, we study existing non-contextual proof techniques for a particular canonical contextual equivalence. In contrast to standard process calculi, reasoning on cryptographic processes must take into account the partial knowledge of the environment about transmitted messages. In the setting of the spi calculus, several notions of environment-sensitive bisimulation has been developed to treat this environment knowledge. We exhibit distinguishing examples between several of these notions, including ones previously believed to coincide. We then give a general framework for comparison of environment-sensitive relations, based on a comparison of the corresponding kinds of environment and notions of environment consistency. Within this framework we perform an exhaustive comparison of the different bisimulations, where every possible relation that is not proven is disproven. For the second step, we consider the question of which expression languages are suitable. Extending the expression language to account for more sophisticated cryptographic primitives or other kinds of data terms quickly leads to decidability issues. Two important problems in this area are the knowledge problem and an indistinguishability problem called static equivalence. It is known that decidability of static equivalence implies decidability of knowledge in many cases; we exhibit an expression language where knowledge is decidable but static equivalence is not. We then define a class of constructor-destructor expression languages and prove that environment consistency over any such language directly corresponds to static equivalence in a particular extension thereof. We proceed to place some loose constraints on deterministic expression evaluation, and redefine the spi calculus in this more general setting. Once we have chosen an expression language, we encounter a third problem, which is inherent in the operational semantics of message-passing process calculi: The possibility to receive arbitrary messages gives rise to infinite branching on process input. To mitigate this problem, we define a symbolic semantics, where the substitution of received messages for input variables never takes place. Instead, input variables are only subject to logical constraints. We then use this symbolic semantics to define a symbolic bisimulation that is sound and complete with respect to its concrete counterpart, extending the possibilities for automated bisimulation checkers.
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| 17. |
- Bröde, Peter, et al.
(författare)
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Non-evaporative effects of a wet mid layer on heat transfer through protective clothing
- 2008
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Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6327 .- 1439-6319. ; 104:2, s. 341-349
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Tidskriftsartikel (refereegranskat)abstract
- In order to assess the non-evaporative components of the reduced thermal insulation of wet clothing, experiments were performed with a manikin and with human subjects in which two layers of underwear separated by an impermeable barrier were worn under an impermeable overgarment at 20 °C, 80% RH and 0.5 ms-1 air velocity. By comparing manikin measurements with dry and wetted mid underwear layer, the increase in heat loss caused by a wet layer kept away from the skin was determined, which turned out to be small (5-6 Wm-2), irrespective of the inner underwear layer being dry or wetted, and was only one third of the evaporative heat loss calculated from weight change, i.e. evaporative cooling efficiency was far below unity. In the experiments with 8 males, each subject participated in two sessions with the mid underwear layer either dry or wetted, where they stood still for the first 30 minutes and then performed treadmill work for 60 minutes. Reduced heat strain due to lower insulation with the wetted mid layer was observed with decreased microclimate and skin temperatures, lowered sweat loss and cardiac strain. Accordingly, total clothing insulation calculated over the walking period from heat balance equations was reduced by 0.02 m2 °C W-1 (16%), while for the standing period the same decrease in insulation, representing 9% reduction only showed up after allowing for the lower evaporative cooling efficiency in the calculations. As evaporation to the environment and inside the clothing was restricted, the observed small alterations may be attributed to the wet mid layer’s increased conductivity, which, however, appears to be of minor importance compared to the evaporative effects in the assessment of the thermal properties of wet clothing.
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| 18. |
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| 19. |
- Croitoru, Victor, et al.
(författare)
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RNA chaperone activity of translation initiation factor IF1
- 2006
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Ingår i: Biochimie. - : Elsevier BV. - 0300-9084 .- 1638-6183. ; 88:12, s. 1875-1882
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Tidskriftsartikel (refereegranskat)abstract
- Translation initiation factor IF1 is an indispensable protein for translation in prokaryotes. No clear function has been assigned to this factor so far. In this study we demonstrate an RNA chaperone activity of this protein both in vivo and in vitro. The chaperone assays are based on in vivo or in vitro splicing of the group I intron in the thymidylate synthase gene (td) from phage T4 and an in vitro RNA annealing assay. IF1 wild-type and mutant variants with single amino acid substitutions have been analyzed for RNA chaperone activity. Some of the IF1 mutant variants are more active as RNA chaperones than the wild-type. Furthermore, both wild-type IF1 and mutant variants bind with high affinity to RNA in a band-shift assay. It is suggested that the RNA chaperone activity of IF1 contributes to RNA rearrangements during the early phase of translation initiation.
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| 20. |
- Croitoru, Victor, 1976-
(författare)
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Study on the Function of Translation Initiation Factor IF1
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Initiation is the first step in protein biosynthesis representing a fundamental event in cell life which determines fidelity, efficiency and regulation of gene expression. In addition to the ribosome and mRNA, three protein factors IF1, IF2 and IF3 are involved in the initiation of translation in prokaryotes. Several minor functions have been attributed to the smallest of these factors, IF1. However, the main function of IF1 remains to be elucidated.In order to investigate the role of this protein in the initiation process we have mutated the corresponding gene infA. Using a high-copy plasmid and site-directed mutagenesis, the six arginine residues of IF1 were separately altered to leucine or aspartate. Another set of plasmid-encoded IF1 mutants with a cold-sensitive phenotype was collected using localized random mutagenesis. This strategy was followed by deletion of the chromosomal infA gene. All variants with a mutated infA gene on a plasmid and a deletion of the chromosomal infA copy were viable, except for an R65D alteration. Several of the mutated infA genes were successfully recombined into the chromosome thereby replacing the wild-type allele. Some of these mutants displayed reduced growth rates and a partial cold-sensitive phenotype.The influence of the leucine group of mutants in IF1 on the expression of two reporter genes with different initiation and/or +2 codons has been investigated. Our results do not indicate any involvement of IF1 in recognition of the +2 codon immediately following the start codon, thus representing the A-site. In addition, this group of mutants has no changed efficiency of decoding at the near-cognate initiation codons UUG and GUG. However, one cold-sensitive IF1 mutant shows a general overexpression of both reporter genes, in particular at low temperatures. Overall, the results do not support the hypothesis that IF1 could possess codon discriminatory functions while blocking the A-site of the ribosome.In this study we also identify that IF1 has RNA chaperone activity both in vitro and in vivo. The chaperone assays are based on splicing of the group I intron in the thymidylate synthase gene (td) from phage T4. Some of the IF1 mutant variants are more active as RNA chaperones than the wild-type. Both wild-type IF1 and mutant variants bind with high affinity to RNA in a band-shift assay. It is suggested that the RNA chaperone activity of IF1 contributes to RNA rearrangements during the early phase of translation initiation.
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| 21. |
- Elperin, Tov, et al.
(författare)
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Clustering of aerosols in atmospheric turbulent flow
- 2007
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Ingår i: Environmental Fluid Mechanics. - : Springer Science and Business Media LLC. - 1567-7419 .- 1573-1510. ; 7:2, s. 173-193
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Tidskriftsartikel (refereegranskat)abstract
- A mechanism of formation of small-scale inhomogeneities in spatial distributions of aerosols and droplets associated with clustering instability in the atmospheric turbulent flow is discussed. The particle clustering is a consequence of a spontaneous breakdown of their homogeneous space distribution due to the clustering instability, and is caused by a combined effect of the particle inertia and a finite correlation time of the turbulent velocity field. In this paper a theoretical approach proposed in Elperin et al. (2002) Phys Rev E 66:036302 is further developed and applied to investigate the mechanisms of formation of small-scale aerosol inhomogeneities in the atmospheric turbulent flow. The theory of the particle clustering instability is extended to the case when the particle Stokes time is larger than the Kolmogorov time scale, but is much smaller than the correlation time at the integral scale of turbulence. We determined the criterion of the clustering instability for the Stokes number larger than 1. We discussed applications of the analyzed effects to the dynamics of aerosols and droplets in the atmospheric turbulent flow.
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| 22. |
- Engström, Johan A Skifs, 1973, et al.
(författare)
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Real-Time Distraction Countermeasures
- 2008
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Ingår i: Driver Distraction: Theory, Effects, and Mitigation. - 9781420007497 ; , s. 465-484
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In general terms, distraction can be defi ned as misallocated attention.1 In the context of driving, distraction could be induced by a range of activities such as looking after children, looking for road signs, applying makeup, and using in-vehicle information systems. Distraction may also be purely “internally” triggered, for example when daydreaming. A large body of empirical research links driver distraction to degraded driving performance, for example, reduced lateral control, reduced event and object detection performance, and impaired decision making (see, e.g., Young et al.2 for a review). Distraction has also repeatedly been identifi ed as a major contributing factor in crashes, 3-5 although direct causal links between distraction-induced performance degradation and actual crash risk have been diffi cult to establish empirically. This is due mainly to the methodological diffi culties associated with collecting suffi ciently detailed precrash data. However, recent results from naturalistic fi eld studies, such as the 100-car study, 6, 7 have contributed to bridging this gap (see Chapters 16 and 17), by demonstrating signifi cant increases in (relative) risk resulting from driver engagement in a variety of distracting activities.
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| 23. |
- Estrada, Karol, et al.
(författare)
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A genome-wide association study of northwestern Europeans involves the C-type natriuretic peptide signaling pathway in the etiology of human height variation.
- 2009
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Ingår i: Human molecular genetics. - : Oxford University Press (OUP). - 1460-2083 .- 0964-6906. ; 18:18, s. 3516-24
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Tidskriftsartikel (refereegranskat)abstract
- Northwestern Europeans are among the tallest of human populations. The increase in body height in these people appears to have reached a plateau, suggesting the ubiquitous presence of an optimal environment in which genetic factors may have exerted a particularly strong influence on human growth. Therefore, we performed a genome-wide association study (GWAS) of body height using 2.2 million markers in 10 074 individuals from three Dutch and one German population-based cohorts. Upon genotyping, the 12 most significantly height-associated single nucleotide polymorphisms (SNPs) from this GWAS in 6912 additional individuals of Dutch and Swedish origin, a genetic variant (rs6717918) on chromosome 2q37.1 was found to be associated with height at a genome-wide significance level (P(combined) = 3.4 x 10(-9)). Notably, a second SNP (rs6718438) located approximately 450 bp away and in strong LD (r(2) = 0.77) with rs6717918 was previously found to be suggestive of a height association in 29 820 individuals of mainly northwestern European ancestry, and the over-expression of a nearby natriuretic peptide precursor type C (NPPC) gene, has been associated with overgrowth and skeletal anomalies. We also found a SNP (rs10472828) located on 5p14 near the natriuretic peptide receptor 3 (NPR3) gene, encoding a receptor of the NPPC ligand, to be associated with body height (P(combined) = 2.1 x 10(-7)). Taken together, these results suggest that variation in the C-type natriuretic peptide signaling pathway, involving the NPPC and NPR3 genes, plays an important role in determining human body height.
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| 24. |
- Goedecke, Julia H, et al.
(författare)
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Differential effects of abdominal adipose tissue distribution on insulin sensitivity in black and white South African women
- 2009
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Ingår i: Obesity. - : Wiley. - 1930-7381 .- 1930-739X. ; 17:8, s. 1506-1512
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Tidskriftsartikel (refereegranskat)abstract
- Black South African women are more insulin resistant than BMI-matched white women. The objective of the study was to characterize the determinants of insulin sensitivity in black and white South African women matched for BMI. A total of 57 normal-weight (BMI 18-25 kg/m(2)) and obese (BMI > 30 kg/m(2)) black and white premenopausal South African women underwent the following measurements: body composition (dual-energy X-ray absorptiometry), body fat distribution (computerized tomography (CT)), insulin sensitivity (S(I), frequently sampled intravenous glucose tolerance test), dietary intake (food frequency questionnaire), physical activity (Global Physical Activity Questionnaire), and socioeconomic status (SES, demographic questionnaire). Black women were less insulin sensitive (4.4 +/- 0.8 vs. 9.5 +/- 0.8 and 3.0 +/- 0.8 vs. 6.0 +/- 0.8 x 10(-5)/min/(pmol/l), for normal-weight and obese women, respectively, P < 0.001), but had less visceral adipose tissue (VAT) (P = 0.051), more abdominal superficial subcutaneous adipose tissue (SAT) (P = 0.003), lower SES (P < 0.001), and higher dietary fat intake (P = 0.001) than white women matched for BMI. S(I) correlated with deep and superficial SAT in both black (R = -0.594, P = 0.002 and R = 0.495, P = 0.012) and white women (R = -0.554, P = 0.005 and R = -0.546, P = 0.004), but with VAT in white women only (R = -0.534, P = 0.005). In conclusion, body fat distribution is differentially associated with insulin sensitivity in black and white women. Therefore, the different abdominal fat depots may have varying metabolic consequences in women of different ethnic origins.
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| 25. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
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Infrared–x-ray pump-probe spectroscopy of the NO molecule
- 2005
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:1
-
Tidskriftsartikel (refereegranskat)abstract
- Two color infrared-x-ray pump-probe spectroscopy of the NO molecule is studied theoretically and numerically in order to obtain a deeper insight of the underlying physics and of the potential of this suggested technology. From the theoretical investigation a number of conclusions could be drawn: It is found that the phase of the infrared field strongly influences the trajectory of the nuclear wave packet, and hence, the x-ray spectrum. The trajectory experiences fast oscillations with the vibrational frequency with a modulation due to the anharmonicity of the potential. The dependences of the x-ray spectra on the delay time, the duration, and the shape of the pulses are studied in detail. It is shown that the x-ray spectrum keep memory about the infrared phase after the pump field left the system. This memory effect is sensitive to the time of switching-off the pump field and the Rabi frequency. The phase effect takes maximum value when the duration of the x-ray pulse is one-fourth of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The manifestation of the phase is different for oriented and disordered molecules and depends strongly on the intensity of the pump radiation.
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| 26. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
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Phase sensitive x-ray absorption driven by strong infrared fields
- 2005
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 71:4
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper it is demonstrated that electron vibrational absorption of molecules driven by strong IR field provides rich physical interpretations of dynamical processes on a short time scale. The phase of an infrared field influences strongly the trajectory of the nuclear wave packet and the probing spectrum. It is shown that the probe spectrum keeps memory of the infrared phase even after that the pump field left the system. The phase effect takes maximum value when the duration of the probe pulse is of the order of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The phase effect is different for oriented and disordered molecules and depends strongly on the intensity of pump radiation. It can be an effective tool to study charge transfer processes like proton transfer in hydrogen bonded networks.
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| 27. |
- Hernandez, Victor Agmo, et al.
(författare)
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The adhesion and spreading of thrombocyte vesicles on electrode surfaces
- 2008
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Ingår i: Bioelectrochemistry. - : Elsevier BV. - 1567-5394 .- 1878-562X. ; 74, s. 210-216
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of thrombocyte vesicles with the surface of metal electrodes, i.e., mercury, gold and gold electrodes modified with self assembled monolayers (SAM), was studied with the help of chronoamperometry, atomic force microscopy, and quartz crystal microbalance measurements. The experimental results show that the interaction of the thrombocyte vesicles with the surface of the electrodes depends on the hydrophobicity of the latter: whereas on very hydrophobic surfaces (mercury and gold functionalized with SAM) the thrombocyte vesicles disintegrate and form a monolayer of lipids. on the less hydrophobic gold surface a bilayer is formed. The chronoamperometric measurements indicate the possibility of future applications to probe membrane properties of thrombocytes. (C) 2008 Elsevier B.V. All rights reserved.
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| 28. |
- Kifle, Mengistu, et al.
(författare)
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Interplay of cost and adoption of tele-medicine in Sub-Saharan Africa : The case of tele-cardiology in Ethiopia
- 2006
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Ingår i: Information Systems Frontiers. - : Springer Science and Business Media LLC. - 1387-3326 .- 1572-9419. ; 8:3, s. 211-223
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Tidskriftsartikel (refereegranskat)abstract
- ...the barriers to diffusion of Tele-Medicine are not entirely technical. Cost has to simultaneously satisfy a number of stakeholders... (Anderson, Aydin and Jay, et al., 1994).Rising costs of the provision of healthcare have been a major issue for debate in both developing and developed countries. This is especially true of very capitalistic societies such as the United States where privatization of the healthcare sector has left many with little or no affordable healthcare. The situation is even worse in developing economies. Developing countries deal with various problems in the provision of health services and healthcare Tan et al. (E-medicine diffusion: E-medicine in Developed and Developing countries. Chapter 8 in E-health paradigm shift: Perspectives, domains and challenges. In Tan J. (Ed.), Imprint of Wiley, New York, Jossey-Bass, 2005). Some of these problems include acute shortages of healthcare professionals and medical facilities Mbarika et al. (Journal of the Association for Information Systems (JAIS) 2005;6(5):130-170). Such shortages have resulted in growing numbers of middle to upper-class citizens of developing countries traveling abroad to seek necessary health services. Using a multi-method case study research, this paper examines the role of Tele-Medicine in the healthcare system and analyzes the costs and benefits of introducing Tele-Cardiology services in Ethiopia (a Sub-Saharan African country). This is a cost comparison study for the treatment of cardiac patients traveling abroad versus patients treated via Tele-Cardiology. Our findings show that Tele-Cardiology is clinically more feasible and more cost effective compared to patients traveling abroad for treatment.
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| 29. |
- Kifle, Mengistu, et al.
(författare)
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Telemedicine in sub-Saharan Africa : The case of teleophthalmology and eye care in Ethiopia
- 2006
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Ingår i: Journal of The American Society For Information Science And Technology. - : Wiley. - 1532-2882 .- 1532-2890. ; 57:10, s. 1383-1393
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Tidskriftsartikel (refereegranskat)abstract
- The authors examine the need and adoption of teleophthalmology in sub-Saharan Africa. Ethiopia, like most sub-Saharan African countries, is faced with limited specialists and health care services. These services are often concentrated in the urban areas, leaving most of the rural population (about 70% of the country) without adequate and timely health care delivery. In Ethiopia, the ratio of ophthalmologists to the population is 1:1,200,000, resulting in inadequate delivery of ophthalmology-related health care services. Using both primary and secondary data collection approaches, the authors report the need for telemedicine as well as the adoption and application of teleophthalmology in Ethiopia. Further, they present Ethiopia's teleophthalmology network, integrated teleconsultation, and teleeducation services. The authors conclude by presenting this research as a starting point to investigate further teleophthalmology and other telemedicine services for Ethiopia and by extension, other developing countries. Therefore, they bring a much-underresearched region (sub-Saharan Africa) and a much-underresearched technology (telemedicine) to the forefront of information systems (IS) research. It is the authors' hope that colleagues in the field will be motivated to investigate this '' forgotten '' region of the world that is yet to reap the full potentials of information and communications technologies (ICTs).
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| 30. |
- Kirsch-Pinheiro, M., et al.
(författare)
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Context grouping mechanism for context distribution in ubiquitous environments
- 2008
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Ingår i: OTM 2008 Confederated International Conferences CoopIS, DOA, GADA, IS, and ODBASE 2008. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 3540888705 - 9783540888703 ; , s. 571-588
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Konferensbidrag (refereegranskat)abstract
- Context distribution is a key aspect for successful applications within mobile and ubiquitous computing environments. In such environments, context information is acquired by several and multiple context sensors distributed over the environment. Applications collect and react to these data, according to predefined adaptation mechanisms. The success of these mechanisms depends on the availability of context information, which is disseminated over the network. However, in practice, only a fraction of the observable context information is required by the adaptation mechanisms. Moreover, for privacy reasons, it is important to delimitate a scope for context dissemination. In this work we address these issues by proposing a context grouping mechanism which allows the definition of groups based on the context characteristics. Each group is defined by these characteristics and delimitate a given context information set that can be distributed among group members. This approach of context grouping acts as a two-fold mechanism. On the one hand, it controls and organizes context distribution over a peer-to-peer network. On the other hand, it proposes a primary and low-level privacy mechanism for context distribution, which is an important aspect influencing context distribution.
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| 31. |
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| 32. |
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| 33. |
- Kunin, Victor, et al.
(författare)
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Measuring genome conservation across taxa: divided strains and united kingdoms
- 2005
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Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 1362-4962. ; 33:2, s. 616-621
-
Tidskriftsartikel (refereegranskat)abstract
- Species evolutionary relationships have traditionally been defined by sequence similarities of phylogenetic marker molecules, recently followed by whole-genome phylogenies based on gene order, average ortholog similarity or gene content. Here, we introduce genome conservation—a novel metric of evolutionary distances between species that simultaneously takes into account, both gene content and sequence similarity at the whole-genome level. Genome conservation represents a robust distance measure, as demonstrated by accurate phylogenetic reconstructions. The genome conservation matrix for all presently sequenced organisms exhibits a remarkable ability to define evolutionary relationships across all taxonomic ranges. An assessment of taxonomic ranks with genome conservation shows that certain ranks are inadequately described and raises the possibility for a more precise and quantitative taxonomy in the future. All phylogenetic reconstructions are available at the genome phylogeny server: .
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| 34. |
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| 35. |
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| 36. |
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| 37. |
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| 38. |
- Peralvarez-Marin, Alex, et al.
(författare)
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Inter-helical hydrogen bonds are essential elements for intra-protein signal transduction : The role of Asp115 in bacteriorhodopsin transport function
- 2007
-
Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 368:3, s. 666-676
-
Tidskriftsartikel (refereegranskat)abstract
- The behavior of the D115A mutant was analyzed by time-resolved UV-Vis and Fourier transformed infrared (FTIR) spectroscopies, aiming to clarify the role of Asp115 in the intra-protein signal transcluctions occurring during the bacteriorhodopsin photocycle. UV-Vis data on the D115A mutant show severely desynchronized photocycle kinetics. FTIR data show a poor transmission of the retinal isomerization to the chromoprotein, evidenced by strongly attenuated helical changes (amide 1), the remarkable absence of environment alterations and protonation/deprotonation events related to Asp96 and direct Schiff base (SB) protonation form the bulk. This argues for the interactions of Asp115 with Leu87 (via water molecule) and Thr90 as key elements for the effective and vectorial proton path between Asp96 and the SB in the cytoplasmic half of bacteriorhodopsin. The results strongly suggest the presence of a regulation motif enclosed in helices C and D (Thr90-Pro91/Asp115) which drives properly the dynamics of helix C through a set of interactions. It also supports the idea that intra-helical hydrogen bonding clusters in the buried regions of transmembrane proteins can be potential elements in intra-protein signal transduction.
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| 39. |
- Polyutov, Sergey, et al.
(författare)
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Self-sustained pulsation of amplified spontaneous emission of molecules in solution
- 2006
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:2, s. 215-227
-
Tidskriftsartikel (refereegranskat)abstract
- Temporal oscillations of amplified spontaneous emission of molecules are studied theoretically. From the proposed theory and numerical simulations, it is found that the self-pulsations originate in an interplay between stimulated emission and saturable absorption. A stability analysis demonstrates the crucial role of the photoabsorption in this process, which can be regulated by a proper choice of buffer molecules. Variations in the saturable absorption mediate a transition from damped oscillations to self-sustained pulsations. The role of propagation effects as well as of the interaction of co- and counter-propagating pulses is also investigated. Numerical simulations, demonstrating the theoretical findings, are performed for a model 3-level system and for an organic chromophore; 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4'-(6-hydroxyhexyl sulphonyl) stilbene.
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| 40. |
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| 41. |
- Verkleij, Chantal J. N., et al.
(författare)
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The effects of hyperglycaemia on thrombin-activatable fibrinolysis inhibitor
- 2009
-
Ingår i: Thrombosis and Haemostasis. - 0340-6245. ; 102:3, s. 460-468
-
Tidskriftsartikel (refereegranskat)abstract
- Epidemiological studies have shown a strong association between type 2 diabetes mellitus and cardiovascular diseases, and hypofibrinolysis may contribute to this phenomenon. The aim of this study was to determine the effect of hyperglycaemia on thrombin-activatable fibrinolysis inhibitor (TAR). Hyperglycaemia was mimicked in vitro by incubation of TAFI with glyceraldehyde and in vivo by hyperglycaemic clamping of healthy volunteers. The effects of long-term hyperglycaemia in vivo on TAR were investigated by comparing TAFI from poorly regulated and tightly regulated patients with type 2 diabetes. In vitro glycated TAR showed an altered migration pattern on SDS-PAGE due to aggregation. Glycated TAFI showed decreased activity after activation by thrombin-thrombomodulin in a glyceraldehyde-dose-dependent manner and a reduced anti-fibrinolytic potential. In vivo, no differences in TAR parameters were found after hyperglycaemic clamping of healthy volunteers and between tightly and poorly regulated patients with type 2 diabetes. Moreover, TAR purified from poorly regulated and tightly regulated patients with type 2 diabetes migrated similarly on SDS-PAGE, indicating little or no glycation of the protein. Despite the deleterious effects of glycation of TAR in vitro on its function,TAFI was neither affected by hyperglycaemic clamping, nor by long-term hyperglycaemia in patients with type 2 diabetes. This is in contrast to fibrinolytic factors as plasminogen-activator inhibitor I and tissue-type plasminogen activator, which are affected. We therefore hypothesise that a normally functioning TAR under hyperglycaemic conditions may tip the haemostatic balance towards hypofibrinolysis, which may contribute to the development of cardiovascular diseases in type 2 diabetic patients.
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| 42. |
- Whale, Mark, et al.
(författare)
-
Analysis of two ALMA Front End Receiver Channels using Physical Optics
- 2008
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Ingår i: Proc of SPIE, Terahertz Technology and Applications. ; 6893, s. 68930D-1
-
Konferensbidrag (refereegranskat)abstract
- The Atacama Large Millimetre Array will be a single research instrument composed of up to 50 high precision antennas, located at the Chajnantor plain in the district of San Pedro de Atacama, 5000m above sea level. Each ALMA telescope will contain 10 frequency channels/bands, ranging from 30 to 950GHz. Radiation from the secondary reflector is collected to the receivers of each wavelength channel through their accompanying front end optics. We present a full electromagnetic treatment of the front end optics for band 5 (163 - 211 GHz) and band 9 (602 - 720 GHz). A full quasi optical and physical optics analysis of the band 5 front end optics, using the antenna analysis tool, GRASP9 [1] is presented. Potential optimisation for the system is presented, namely a reflector edge taper and a comparison of two surface geometries. A similar analysis of the band 9 system is presented. Full electromagnetic simulations are compared with cold beam pattern measurements made at the Space Research Organisation of the Netherlands [2, 3]. Analysis of the effect of the polarizing grid is presented, with suggested modifications to improve cross polar levels
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| 43. |
- Wood, Laura D, et al.
(författare)
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The genomic landscapes of human breast and colorectal cancers.
- 2007
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 318:5853, s. 1108-1113
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Tidskriftsartikel (refereegranskat)abstract
- Human cancer is caused by the accumulation of mutations in oncogenes and tumor suppressor genes. To catalog the genetic changes that occur during tumorigenesis, we isolated DNA from 11 breast and 11 colorectal tumors and determined the sequences of the genes in the Reference Sequence database in these samples. Based on analysis of exons representing 20,857 transcripts from 18,191 genes, we conclude that the genomic landscapes of breast and colorectal cancers are composed of a handful of commonly mutated gene "mountains" and a much larger number of gene "hills" that are mutated at low frequency. We describe statistical and bioinformatic tools that may help identify mutations with a role in tumorigenesis. These results have implications for understanding the nature and heterogeneity of human cancers and for using personal genomics for tumor diagnosis and therapy.
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| 44. |
- Yavuz, Emre A., et al.
(författare)
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A practical method for estimating performance metrics of call admission control schemes in wireless mobile networks
- 2005
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Ingår i: 2005 IEEE Wireless Communications and Networking Conference, Vols 1-4. - 0780389662 ; , s. 1254-1259
-
Konferensbidrag (refereegranskat)abstract
- Providing the desired call blocking probability to not only new but also existing calls has been a challenge for wireless mobile network service providers. To satisfy different requirements for new and handoff call blocking probabilities, several call admission control (CAC) schemes have been proposed in the literature. Exact analysis of these schemes using two dimensional Markov chain is computationally intensive. Therefore under specific assumptions computationally efficient methods to analyze these systems using one dimensional Markov chain models have been considered. The "traditional" approach assumes that channel holding time for new and handoff calls have equal mean values. While the "normalized" approach relaxes this assumption, it is accurate only for the new call bounding CAC scheme. In this paper, we reevaluate the analytical methods for computing call blocking probabilities for several widely known call admission control schemes under more general assumptions by providing an easy to implement method. The numerical results show that when the average values of channel holding times for new and handoff calls are different, the proposed approach gives more accurate results when compared with the traditional and normalized methods based on one dimensional Markov chain modeling, while keeping the computational complexity low.
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| 45. |
- Yavuz, Emre A., et al.
(författare)
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Computationally efficient method to evaluate the performance of guard-channel-based call admission control in cellular networks
- 2006
-
Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 55:4, s. 1412-1424
-
Tidskriftsartikel (refereegranskat)abstract
- Many guard-channel-based call admission control (CAC) schemes for cellular networks have been proposed to provide the desired quality of service to not only new calls but also ongoing calls when they hand off to neighboring cells. Blocking/dropping probabilities of new/handoff calls are generally analyzed using one-dimensional Markov chain modeling under specific assumptions to avoid solving large sets of flow equations that makes exact analyses of these schemes using multidimensional Markov chain models infeasible. This is the case with the "traditional" approach, which assumes that channel holding times for new and handoff calls have equal mean values, and the "normalized" approach, which relaxes this assumption but is accurate only for the new call bounding CAC scheme. In this paper, we reevaluate the analytical methods for computing new/handoff call blocking/dropping probabilities for several widely known CAC schemes and develop an easy-to-implement method under more general assumptions. Numerical results show that when the mean channel holding times for new and handoff calls are different, the proposed "effective holding time" approach gives more accurate results compared with the traditional and the normalized methods while keeping the computational complexity low. The accuracy of these methods and their levels of computational complexity with the exact solution are also compared.
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| 46. |
- Yavuz, Emre A., et al.
(författare)
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Efficient approximations for call admission control performance evaluations in multi-service networks
- 2006
-
Ingår i: GLOBECOM 2006. - 9781424403561
-
Konferensbidrag (refereegranskat)abstract
- Several dynamic call admission control (CAC) schemes for cellular networks have been proposed in the literature to reserve resources adaptively to provide the desired quality of service (QoS) to not only high priority calls but also to low priority ones. Efficient adaptive reservations depend on reliable and up-to-date system status feedback provided to the CAC mechanism. However exact analysis of these schemes using multidimensional Markov chain models are intractable in real time due to the need to solve large sets of flow equations. Hence performance metrics such as call blocking probabilities of various QoS classes are generally evaluated using one dimensional Markov chain models assuming that channel occupancy times for all QoS classes have equal mean values and all arriving calls have equal capacity requirements. In this paper we re-evaluate the analytical methods to compute call blocking probabilities of various QoS classes for several widely known CAC schemes by relaxing these assumptions, and propose a novel approximation method for performance evaluation with low computational complexity. Numerical results show that proposed method provides results that match well with the exact solutions.
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| 47. |
- Yavuz, Emre A., et al.
(författare)
-
Efficient Methods for Performance Evaluations of Call Admission Control Schemes in Multi-Service Cellular Networks
- 2008
-
Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276 .- 1558-2248. ; 7:9, s. 3468-3476
-
Tidskriftsartikel (refereegranskat)abstract
- Many dynamic call admission control (CAC) schemes have been proposed in the literature for adaptive reservations in cellular networks. Efficient application of these schemes requires reliable and up-to-date feedback of system performance to the CAC mechanism. However, exact analyses of these schemes in real time using multi-dimensional Markov chain models are challenging due to the need to solve large sets of flow equations. One dimensional Markov chain models have been widely used to derive performance metrics such as call blocking probabilities of multiple traffic classes assuming that all classes of calls have equal capacity requirements and exponentially distributed channel holding times with equal mean values. These assumptions need to be relaxed for a more general evaluation of CAC performance in multi-service cellular networks. In this paper we classify CAC schemes according to their Markov chain models into two categories: symmetric and asymmetric, and develop computationally efficient analytical methods to compute call blocking probabilities of various traffic classes for several widely known CAC schemes under relaxed assumptions. We obtain a product form solution to evaluate symmetric schemes and propose a novel performance evaluation approximation method with low computational cost for asymmetric schemes. Numerical results demonstrate the accuracy and efficiency of the proposed method.
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| 48. |
- Yavuz, Emre A., et al.
(författare)
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Modelling channel occupancy times for voice traffic in cellular networks
- 2007
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Ingår i: 2007 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-14. - 9781424403523 ; , s. 332-337
-
Konferensbidrag (refereegranskat)abstract
- Call holding times in telephony networks are commonly approximated by exponential distributions to facilitate traffic engineering. However, for traffic engineering of cellular networks, channel occupancy times need to be modeled instead to facilitate analytical modeling or to feed network simulations. In this paper, we classify channel occupancy times and present an empirical study based on data obtained from a real cellular network to determine which probability distribution functions can approximate them better. The results are environment dependent, but no assumptions that can be influential are made, as opposed to previous analytical and simulation studies which results are highly dependent on the assumptions made by the authors. We show that all types of channel occupancy times can be approximated by lognormal distribution. For stationary users, channel occupancy times are commonly approximated by exponential distribution due to its tractability, assuming that cell residence times are also exponentially distributed. However, we show that lognormal distribution fits much better to both channel occupancy and call holding times regardless of whether users are stationary or mobile.
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