| 1. |
- Andersson, Christin, et al.
(författare)
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Increasing CSF phospho-tau levels during cognitive decline and progression to dementia
- 2008
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Ingår i: Neurobiology of Aging. - : Elsevier BV. - 0197-4580 .- 1558-1497. ; 29:10, s. 1466-1473
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Little is known about longitudinal changes of cerebrospinal fluid (CSF) biomarkers during cognitive decline in neurodegenerative disease progression. OBJECTIVE: To investigate longitudinal changes in CSF biomarkers--total-tau (T-tau), phospho-tau (P-tau) and beta-amyloid (Abeta42)--during cognitive decline. METHODS: Forty memory clinic patients (47.5% females), aged 61.3+/-7.6 (S.D.) years, non-demented at baseline, underwent lumbar puncture and neuropsychological testing at two occasions. Baseline mean MMSE-score was 28.3+/-1.8. Patients were divided into three groups based on baseline memory functioning; severely impaired (SIM), moderately impaired (MIM) and no impairment (NIM). RESULTS: There was a significant increase in P-tau in the SIM-group during follow-up, while P-tau in MIM and NIM did not change. Eighty-three percent of the SIM-patients converted to dementia (80% AD), while most MIM- and NIM-patients remained non-demented. T-tau- and Abeta42-levels did not change in any of the memory groups during follow-up. CONCLUSION: Increasing P-tau levels during cognitive decline and conversion to dementia suggest that P-tau may be useful as a longitudinal marker of the neurodegenerative process.
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| 2. |
- Andersson, Magnus, et al.
(författare)
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Physical Properties of Biopolymers Assessed by Optical Tweezers : Analysis of folding and refolding of bacterial pili
- 2008
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Ingår i: ChemPhysChem. - : Wiley-VCH Verlagsgesellschaft. - 1439-4235 .- 1439-7641. ; 9:2, s. 221-235
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial adhesion to surfaces mediated by specific adhesion organelles that promote infections, as exemplified by the pili of uropathogenic E. coli, is studied mostly at the level of cell-cell interactions and thereby reflects the averaged behavior of multiple pili. The role of pilus rod structure has therefore only been estimated from the outcome of experiments involving large numbers of organelles at the same time. It has, however, lately become clear that the biomechanical behavior of the pilus shafts play an important, albeit hitherto rather unrecognized, role in the adhesion process. For example, it has been observed that shafts from two different strains, even though they are similar in structure, result in large differences in the ability of the bacteria to adhere to their host tissue. However, in order to identify all properties of pilus structures that are of importance in the adhesion process, the biomechanical properties of pili must be assessed at the single-molecule level. Due to the low range of forces of these structures, until recently it was not possible to obtain such information. However, with the development of force-measuring optical tweezers (FMOT) with force resolution in the low piconewton range, it has lately become possible to assess forces mediated by individual pili on single living bacteria in real time. FMOT allows for a more or less detailed mapping of the biomechanical properties of individual pilus shafts, in particular those that are associated with their elongation and contraction under stress. This Mi- nireview presents the FMOT technique, the biological model system, and results from assessment of the biomechanical properties of bacterial pili. The information retrieved is also compared with that obtained by atomic force microscopy.
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| 3. |
- Andersson, Ove, et al.
(författare)
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Collapse of an ice clathrate under pressure observed via thermal conductivity measurements
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78, s. 174201-
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Tidskriftsartikel (refereegranskat)abstract
- Irreversible transformation of the tetrahydrofuran ice clathrate at 130 K was studied by measuring thermal conductivity k with increase in pressure p. Initially, k increases slowly with p up to 0.75 GPa where it levels off, is roughly constant up to 0.95 GPa, then decreases up to 1.05 GPa. Pressure collapses the clathrate structure, plausibly beginning with lattice distortion, and k increases at 1.05 GPa in a sharp sigmoid-shape manner due to large densification until the transformation is complete at 1.25 GPa. This is the opposite of that found for ice whose k decreases first slowly with increase in p and then rapidly in an inverted sigmoidshape manner [O. Andersson and H. Suga, Phys. Rev. B 65, 140201 (2002)]. At 1.08 GPa and 131 K, k increases with time t (s) according to exp(t /2945), which is also the opposite of the collapse of ice [G. P. Johari and O. Andersson, Phys. Rev. B 70, 184108 (2004)]. The difference in its behavior is attributed to strong phonon scattering from the tetrahydrofuran guest molecules. k of the collapsed clathrate is 30% less than that for the collapsed ice, which is comparable with the 25% lesser k of the tetrahydrofuran-water solution from k of water at ambient pressure. On depressurizing at 130 K, k decreases progressively more rapidly and k of the collapsed state at 0.3 GPa is slightly lower than that of the as-made clathrate, showing that its original structure is not recovered.
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| 4. |
- Andersson, Ove
(författare)
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Dielectric relaxation of the amorphous ices
- 2008
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Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric properties of the low and high density amorphous ices are discussed in terms of those for supercooled water and crystalline ices, and also used to evaluate the transition behaviour upon pressure cycling at 130 K. The dielectric relaxation of the high density amorphous ice is described well by the symmetrical Cole–Cole function with an almost pressure independent relaxation time τ ∼ 2 s at 133 K and a relaxation time distribution factor of 0.7. At the high to low density amorphous ice transition, the dielectric relaxation time increases by about two orders of magnitude despite a ∼30% decrease in density, and τ of the low density amorphous ice is in the range 102–103 s at 130 K. The relaxation time behaviour of the high density amorphous ice is similar to that of supercooled liquid water, whereas τ of the low density amorphous ice appears to be prolonged by the ice rules, in correspondence to that of the crystalline ices.
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| 5. |
- Andersson, Ove, et al.
(författare)
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Nature of the pressure-induced collapse of an ice clathrate by dielectric spectroscopy
- 2008
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 129:23
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Tidskriftsartikel (refereegranskat)abstract
- Collapse of an ice clathrate of type II structure containing tetrahydrofuran as guest molecules has been studied at different pressures by dielectric spectroscopy. The sample was pressurized to 1.3 GPa at 130 K and the resulting collapsed state was pressure cycled. The dielectric relaxation time increases at a progressively rapid rate during pressurizing and then decreases slowly on depressurizing, but the dielectric relaxation time does not reach the value of the original state. With increase in pressure, the limiting high frequency permittivity due to orientation of H2O molecules first increases by about 5% until 0.75 GPa and then decreases slightly until 1 GPa, and finally it increases until ~1.2 GPa. The decrease is attributed to the loss of contribution from the reorientational motion of tetrahydrofuran molecules and the increase to densification as the structure mechanically collapses completely in the 1–1.25 GPa range. The relaxation time of the collapsed state is comparable with that of the high-density amorph formed on pressure collapse of ice.
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| 6. |
- Björnham, Oscar, 1976-, et al.
(författare)
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Modeling of the elongation and retraction of Escherichia coli P pili under strain by Monte Carlo simulations
- 2008
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Ingår i: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 37:4, s. 381-391
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Tidskriftsartikel (refereegranskat)abstract
- P pili are fimbrial adhesion organelles expressed by uropathogenic Escherichia coli in the upper urinary tract. They constitute a stiff helix-like polymer consisting of a number of subunits joined by head-to-tail bonds. The elongation and retraction properties of individual P pili exposed to strain have been modeled by Monte Carlo (MC) simulations. The simulation model is based upon a three-state energy landscape that deforms under an applied force. Bond opening and closure are modeled by Bells theory while the elongation of the linearized part of the pilus is described by a worm-like chain model. The simulations are compared with measurements made by force measuring optical tweezers. It was found that the simulations can reproduce pili elongation as well as retraction, under both equilibrium and dynamic conditions, including entropic effects. It is shown that the simulations allow for an assessment of various model parameters, e.g. the unfolding force, energy barrier heights, and various distances in the energy landscape, including their stochastic spread that analytical models are unable to do. The results demonstrate that MC simulations are useful to model elongation and retraction properties of P pili, and therefore presumably also other types of pili, exposed to strain and/or stress. MC simulations are particularly suited for description of helix-like pili since these have an intricate self-regulating mechanical elongation behavior that makes analytical descriptions non-trivial when dynamic processes are studied, or if additional interactions in the rod or the behavior of the adhesion tip needs to be modeled.
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| 7. |
- Dmitriev, Vladimir, et al.
(författare)
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Pressure-temperature phase diagram of LiBH4: Synchrotron x-ray diffraction experiments and theoretical analysis
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 77:17
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Tidskriftsartikel (refereegranskat)abstract
- An in situ combined high-temperature high-pressure synchrotron radiation diffraction study has been carried out on LiBH4. The phase diagram of LiBH4 is mapped to 10 GPa and 500 K, and four phases are identified. The corresponding structural distortions are analyzed in terms of symmetry-breaking atomic position shifts and anion ordering. Group-theoretical and crystal-chemical considerations reveal a nontrivial layered structure of LiBH4. The layers and their deformations define the structural stability of the observed phases.
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| 8. |
- Eriksson, Björn, 1981-, et al.
(författare)
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The Dynamic Performance of a Pilot Stage in the Poppet Type Hydraulic Flow Amplifier
- 2008
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Ingår i: The 51st NCFP Technical Conference,2008. - Proceedings of the 51st NCFP Technical Conference : Omnipress. ; , s. 659-
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Konferensbidrag (refereegranskat)abstract
- This paper examines the dynamic properties of the pilot stage in a poppet type two-stage flow control valve of the -Valvistor- type. The particular valve studied is a screw-in Valvistor valve of NG16 size. There are several benefits to this valve type: it has a high closed loop bandwidth and the design allows big flow capacities. An attractive feature of this two-stage valve is that the pilot flow contributes to the total flow giving higher steady state flow efficiency. The dynamic characteristics of the main stage were discussed in an earlier paper. In this paper the aim is to study the influence of the pilot stage of the valve. The bandwidth of this type of valve is often unexpected low. Due to the high bandwidth of the Valvistor element the pilot dynamics is often dominating. In this paper it is shown by measurements the influence of different parts in the pilot valve that limits its bandwidth. Flow forces are used in this valve to compensate the pressure dependency in the flow. It is a common way of design in so called pressure compensated valves. It is discussed in the paper how this flow forces influences the dynamic properties of the pilot valve. The mentioned flow forces interact together with the mechanical spring in the pilot valve. Although the studied valve is just one of many variants of the Valvistor principle, we will investigate it closely due to the interest for this valve among other researchers. One important conclusion is that the inductance of the pilot solenoid is often limiting the bandwidth of the valve as a whole.
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| 9. |
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| 10. |
- Mucci, Lorelei A., et al.
(författare)
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Nine-gene molecular signature is not associated with prostate cancer death in a watchful waiting cohort
- 2008
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Ingår i: Cancer Epidemiology, Biomarkers and Prevention. - Baltimore : Waverly Press. - 1055-9965 .- 1538-7755. ; 17:1, s. 249-251
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Tidskriftsartikel (refereegranskat)abstract
- Tumor molecular markers hold promise to distinguish potentially lethal from indolent prostate cancer and to guide treatment choices. A previous study identified a nine-gene molecular signature in tumors associated with prostate-specific antigen relapse after prostatectomy. We examined this molecular model in relation to prostate cancer death among 172 men with initially localized disease. We quantified protein expression of the nine genes in tumors to classify progression risk. Accounting for clinical prognostic factors, the nine-gene model did not provide discrimination to predict lethal and indolent prostate cancer.
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