| 3551. |
- Ahlberg, Per, et al.
(författare)
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Phosphatised olenid trilobites and associated fauna from the Upper Cambrian of Vastergotland, Sweden
- 2005
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Ingår i: Acta Palaeontologica Polonica. - 0567-7920. ; 50:3, s. 429-440
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Tidskriftsartikel (refereegranskat)abstract
- Secondarily phosphatised olenid trilobites from organic-rich limestones (orsten) in the Furongian (Upper Cambrian) of Vastergotland, south-central Sweden, are described and illustrated. All trilobites originate from the Peltura scarabaeoides Zone and were collected on the western slope of Kinnekulle. Only the dorsal exoskeletons have become secondarily phosphatised, and the ventral appendages are not preserved. Yet the material is otherwise remarkably well preserved and reveals the morphology of the olenid trilobites in greater detail than hitherto known. Species belonging to the genera Ctenopyge, Sphaerophthalmus, Parabolina, and Peltura are identified, and several juvenile specimens are present in the material. The material is disarticulated and fragmentary, and it has only been possible to identify a few specimens to species level. In addition to chaetognaths and conodonts, the trilobites are associated with pelmatozoan columnals, a possible camaroid, and fossils of uncertain affinities. These fossils, along with a probable conulariid fragment from the Peltura minor Zone, are also described and discussed. The presence of a benthic fauna of pelmatozoans, and possible conulariids and camaroids, indicates that at least parts of the Peltura zones were deposited during dysoxic rather than anoxic periods. Moreover, the sea floor must have been firm enough to allow colonisation by sessile organisms.
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| 3552. |
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| 3553. |
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| 3554. |
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| 3555. |
- Ahlberg, Sebastian, et al.
(författare)
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Many-body effects on tracer particle diffusion with applications for single-protein dynamics on DNA
- 2015
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- 30% of the DNA in E. coli bacteria is covered by proteins. Such a high degree of crowding affects the dynamics of generic biological processes (e.g. gene regulation, DNA repair, protein diffusion etc) in ways that are not yet fully understood. In this paper, we theoretically address the diffusion constant of a tracer particle in a one-dimensional system surrounded by impenetrable crowder particles. While the tracer particle always stays on the lattice, crowder particles may unbind to a surrounding bulk and rebind at another, or the same, location. In this scenario we determine how the long time diffusion constant D (after many unbinding events) depends on (i) the unbinding rate of crowder particles k(off), and (ii) crowder particle line density rho, from simulations (using the Gillespie algorithm) and analytical calculations. For small k(off), we find D similar to k(off)/rho(2) when crowder particles do not diffuse on the line, and D similar to root Dk(off)/rho when they are diffusing; D is the free particle diffusion constant. For large k(off), we find agreement with mean-field results which do not depend on k(off). From literature values of k(off) and D, we show that the small k(off) -limit is relevant for in vivo protein diffusion on crowded DNA. Our results apply to single-molecule tracking experiments.
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| 3556. |
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| 3557. |
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| 3558. |
- Ahlborg, Henrik
(författare)
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Changes in bone mass and skeletal structure in the postmenopausal period.
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to evaluate long-term changes in bone mass and skeletal structure in the forearm in the peri- and postmenopausal period. 156 premenopausal women, at baseline aged 48 years, not taking medications and without disease processes known to interfere with bone metabolism, were followed through menopause by measurements of bone mass and skeletal structure at the cortical site of the distal radius by single photon absorptiometry, on average every second year until age 72. General health and life-style factors were reported, and the postmenopausal serum estradiol level and fragility fractures were noted. Menopause was determined according to the definition established by the World Health Organisation. The age-dependent reduction in bone mineral density accelerated after menopause, with the highest bone loss found during the first 5 years following menopause. Independent of age at menopause, premenopausal women with low, age-specific bone mineral density at age 48 years were likely to have low bone mineral density also at age 64 years. Furthermore, menopause was followed by structural geometrical changes such as endosteal resorption, increasing the medullary cavity, and periosteal apposition, increasing the bone size. Increased periosteal apposition was associated with both increased bone loss and low postmenopausal serum levels of estradiol. The periosteal apposition seemed to partly compensate for the decreased bone strength, caused by the decrease in tissue mineral content. A Strength Index, taking both bone density and skeletal geometry into account, predicted a future fracture of the distal radius. If the structural skeletal changes of the distal radius, with enlargement of the medullary cavity, are a general phenomenon of the diaphyseal bones, this theoretically could have implications for the long-term fixation of a hip prosthesis. Bone loss following menopause was less in physically active than in physically inactive women, so that physically active women had a higher bone mineral density at age 72 than physically inactive women. This suggests that moderate physical activity in the postmenopausal period could possibly be recommended as a strategy to prevent bone loss. Furthermore, the effect of hormone replacement therapy on bone loss after menopause was evaluated in an observational study with 28 women with and 196 women without hormone replacement therapy. Hormone replacement therapy seemed to reduce the rate of bone loss over a period of 23 years, and the longer the duration of the therapy, the less the bone loss.
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| 3559. |
- Ahlborg, Henrik, et al.
(författare)
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Contribution of hip strength indices to hip fracture risk in elderly men and women
- 2005
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Ingår i: Journal of Bone and Mineral Research. - 1523-4681. ; 20:10, s. 1820-1827
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Tidskriftsartikel (refereegranskat)abstract
- In this prospective, case-control study, femoral neck diameter, cross-sectional moment of inertia, or section modulus was an independent predictor of hip fracture risk after adjustment for BMD. However, the contribution of each of these indices to hip fracture prediction was modest in the presence of BMD. Introduction: The relative contribution of measures of hip strength to hip fracture prediction is unclear. This study was designed to characterize the association between hip strength indices and hip fracture risk in relation to BMD in elderly men and women. Materials and Methods: Seventy-one women and 25 men >= 60 years of age, who sustained a hip fracture during the study period of 1989-2003, were selected from the prospective, population-based Dubbo Osteoporosis Epidemiology Study. These fracture cases were randomly matched for age and sex in a 1:2 ratio with non-fracture individuals. BMD at the femoral neck was measured before the fracture event by DXA (Lunar DPX-L). Hip strength indices, including femoral neck diameter (FND), cross-sectional moment of inertia (CSMI), and section modulus (Z), were estimated by reanalysis of the image files using hip strength analysis software. Results: In women, after adjustment for BMD, increased risk of hip fracture was associated with smaller FND (OR, 1.6; 95% CI, 1.0, 2.7), lower CSMI (OR, 1.8; 95% Cl, 1.0, 3.2), or Z (OR, 1.6; 95% Cl, 1.1, 5.1). In men, none of these hip strength indices were significant predictors of fracture risk. However, using the results in women as a prior distribution, it was estimated that the BMD-adjusted OR for FND (OR, 1.5; 95% CI, 1.0, 2.3), CSMI (OR, 1.6; 95% CI, 1.0, 2.5), or Z (OR, 2.3; 95% Cl, 1.4,3.9) was each significantly associated with hip fracture risk in men. In the logistic regression model, BMD alone accounted for 32% and 16% of the variance of fracture liability in women and men, respectively. The addition of FND, CSMI, or Z to the model increased the respective variance proportion to 34% and 19%. Conclusions: These data suggest that smaller FND and lower CSMI or Z is an independent risk factor for hip fracture in both women and men. However, the contribution of these measures to hip fracture prediction over and above BMD is likely modest.
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| 3560. |
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