| 1. |
- Kasaba, Y., et al.
(författare)
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The Plasma Wave Investigation (PWI) onboard the BepiColombo/MMO : First measurement of electric fields, electromagnetic waves, and radio waves around Mercury
- 2010
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 58:1-2, s. 238-278
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Tidskriftsartikel (refereegranskat)abstract
- The BepiColombo Mercury Magnetospheric Orbiter (MMO) spacecraft includes the plasma and radio wave observation system called Plasma Wave Investigation (PWI). Since the receivers for electric field, plasma waves, and radio waves are not installed in any of the preceding spacecraft to Mercury, the PWI will provide the first opportunity for conducting in-situ and remote-sensing observations of electric fields, plasma waves, and radio waves in the Hermean magnetosphere and exosphere. These observations are valuable in studying structure, dynamics, and energy exchange processes in the unique magnetosphere of Mercury. They are characterized by the key words of the non-MHD environment and the peculiar interaction between the relatively large planet without ionosphere and the solar wind with high dynamic pressure. The PWI consists of three sets of receivers (EWO, SORBET, and AM(2)P), connected to two sets of electric field sensors (MEFISTO and WPT) and two kinds of magnetic field sensors (LF-SC and DB-SC). The PWI will observe both waveforms and frequency spectra in the frequency range from DC to 10 MHz for the electric field and from 0.3 Hz to 640kHz for the magnetic field. From 2008, we will start the development of the engineering model, which is conceptually consistent with the flight model design. The present paper discusses the significance and objectives of plasma/radio wave observations in the Hermean magnetosphere, and describes the PWI sensors, receivers and their performance as well as the onboard data processing.
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| 7. |
- Boardsen, Scott A., et al.
(författare)
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Observations of Kelvin-Helmholtz waves along the dusk-side boundary of Mercury's magnetosphere during MESSENGER's third flyby
- 2010
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 37
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Tidskriftsartikel (refereegranskat)abstract
- During the third MESSENGER flyby of Mercury on 29 September 2009, 15 crossings of the dusk-side magnetopause were observed in the magnetic field data over a 2-min period, during which the spacecraft traveled a distance of 0.2 R-M (where R-M is Mercury's radius). The quasi-periodic nature of the magnetic field variations during the crossings, the characteristic time separations of similar to 16 s between pairs of crossings, and the variations of the magnetopause normal directions indicate that the signals are likely the signature of surface waves highly steepened at their leading edge that arose from the Kelvin-Helmholtz instability. At Earth, the Kelvin-Helmholtz instability is believed to lead to the turbulent transport of solar wind plasma into Earth's plasma sheet. This solar wind entry mechanism could also be important at Mercury. Citation: Boardsen, S. A., T. Sundberg, J. A. Slavin, B. J. Anderson, H. Korth, S. C. Solomon, and L. G. Blomberg (2010), Observations of Kelvin-Helmholtz waves along the dusk-side boundary of Mercury's magnetosphere during MESSENGER's third flyby, Geophys. Res. Lett., 37, L12101, doi: 10.1029/2010GL043606.
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| 8. |
- Bohlin, Maria, et al.
(författare)
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Affinity studies of beta-2-glycoprotein I using capillary electrophoresis
- 2010
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Konferensbidrag (refereegranskat)abstract
- Beta2-glycoprotein I (b2gpI), also known as apolipoprotein H, is a plasma protein which is involved in the blood coagulation cascade. It binds negatively charged substances such as heparin, DNA, and anionic phospholipids. A number of functions of b2gpI have been proposed, however, the precise function is still not entirely known. Circulating autoantibodies against b2gpI are associated with increased risk of thrombotic events, such as thrombosis and reoccurring fetal loss. It is therefore of interest to functionally characterize b2gpI including the influence of anti-b2gpI autoantibodies on the ligand binding behavior of the protein. The characterization of interactions between biological molecules may be accomplished by capillary electrophoresis under non-denaturing conditions, without the need for immobilization. To avoid charge dependent analyte adsorption to the negative charges of the capillary wall we found the pH hysteresis effect of silica very useful. An acidic pretreatment of the capillary made it possible to perform a subsequent analysis at neutral pH. We were able to perform binding studies between b2gpI and heparin and monosaccharides at different ionic strengths and temperatures in a simple way. We could also study the effect of mildly denaturing conditions on the binding to the different ligands simply by adding sodium dodecyl sulfate (SDS), urea and ACN to the background electrolyte. The approach is simple, fast and automatic. The ionic strength, temperature and other parameters such as denaturing agents could easily be changed to characterize the binding between b2gpI and different ligands.
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| 9. |
- Bohlin, Maria E, 1979-, et al.
(författare)
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Effects of ionic strength, temperature and conformation on affinity interactions of β2-glycoprotein I monitored by capillary electrophoresis
- 2011
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Ingår i: Electrophoresis. - : Wiley. - 0173-0835 .- 1522-2683. ; 32, s. 728-737
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Tidskriftsartikel (refereegranskat)abstract
- We have used CE to evaluate the interaction between β2-glycoprotein I (β2gpI) and heparin. β2gpI is a human plasma protein involved in the blood coagulation cascade. It is of interest to functionally characterize the interactions of β2gpI because the exact function is not entirely known and because circulating autoantibodies against β2gpI are associated with an increased risk of thrombotic events. The effect of the ionic strength, temperature, and conformation of the protein on the interaction between β2gpI and heparin has been studied. The CE procedure for this study is simple, fast and automatic. β2gpI and heparin were allowed to interact during electrophoresis at different ionic strength buffers and at different capillary temperatures. To mimic perturbation of the conformation of β2gpI, different denaturing agents (SDS, ACN and urea) were added to the background electrolyte. While simple 1:1 binding isotherms were obtained at 22 °C the data strongly suggests that at physiological temperature the binding stoichiometry is not 1:1 and/or that cooperative interactions begin to play a role. We found that (i) the KD values differed by a factor of 60 at the ionic strengths studied (ii) β2gpI was resistant to denaturation with SDS and ACN, but was partially denatured by urea and (iii) the KD for the β2gpI-heparin interaction in the presence of urea was 10 times higher than the KD determined at the same conditions without urea added. Therefore, we conclude that the interaction between β2gpI and heparin is dependent on electrostatic interactions and on the conformation of β2gpI.
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| 10. |
- Bohlin, Maria E., 1979-
(författare)
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Method development for affinity capillary electrophoresis of ß2-glycoprotein I and biological ligands
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The final goal of this study is to establish a microscale analysis method that allows solution phase characterization of interactions between β2-glycoprotein I (β2gpI) and some of its ligands. Human β2gpI is a phospholipid- and heparin-binding plasma glycoprotein. The physiological role of the protein in normal blood coagulation is not entirely known, nor is its role in autoimmune diseases characterized by blood clotting disturbances (thrombosis). Quantitative binding data of β2gpI interactions with some of its ligands may help elucidating the mechanisms behind these diseases and in the development of new approaches for diagnostics, prevention, and therapy.In this thesis, capillary electrophoresis (CE) was used as methodological platform for the interaction studies. The analysis of peptides and proteins by CE is desirable due to low sample consumption, possibilities for non-denaturing and highly effective separations. The first objective of this thesis was to find an approach to prevent charge dependent adsorption of β2gpI to the inner surface of the capillaries. Analyte adsorption at the negatively charged inner surface of fused silica capillaries is detrimental to interaction analyses. This phenomenon is especially pronounced in the analysis of basic proteins and proteins containing exposed positively charged domains, such as β2gpI. A new strategy to suppress these solute-wall interactions was devised, investigated and optimized. This strategy exploits the pH hysteresis behavior of fused silica surfaces, by simply performing an acidic pretreatment of the capillary. The results in this thesis show that the acidic pretreatment efficiently prevents protein adsorption.
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| 11. |
- Bohlin, Maria, et al.
(författare)
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Estimation of the amount of β2-glycoprotein I adsorbed at the inner surface of fused silica capillaries after acidic, neutral and alkaline pretreatment
- 2012
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Ingår i: Electrophoresis. - Weinheim, Germany : John Wiley & Sons. - 0173-0835 .- 1522-2683. ; 33:12, s. 1695-1702
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Tidskriftsartikel (refereegranskat)abstract
- Sample adsorption to the inner surface of fused silica capillaries is a common problem inCE when analyzingmacromolecules and is harmful to the analysis. We previously utilizedthe pH hysteresis effect of fused silica to facilitate electrophoresis of the strongly adsorbingprotein β2gpI in plain-fused silica capillaries at neutral pH. In the present paper, theeffect of different pretreatments of the capillary on the adsorption of the β2-glycoproteinI has been investigated using electroosmosis markers, SDS mobilization, and imagingbased on indirect immunofluorescence microscopy for direct visualization. The amountof β2gpI adsorbed on the surface was probed using all these independent techniques afterelectrophoresis at neutral pH on capillaries pretreated with HCl, background electrolyte(BGE), and NaOH. BGE pretreatment was included as a positive control. We found that80% or more of the starting material was adsorbed to the inner surface of the silicacapillaries during electrophoresis after pretreatment with only BGE or with NaOH, butafter acidic pretreatment the loss was consistently less than 20%. NaOH most efficientlyremoves adsorbed protein between runs. A theoretical calculation of the pH change ofthe BGE showed that electrolysis affects the pH more than the deprotonation of silanolsduring electrophoresis. We conclude that acidic pretreatment of fused silica capillariesdiminishes adsorption of β2gpI by decreasing charge-dependent wall adsorption.
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| 12. |
- Bohlin, Maria, et al.
(författare)
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Structure-activity studies of human beta2-glycoprotein I using capillary electrophoresis
- 2011
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Konferensbidrag (refereegranskat)abstract
- We have investigated various modes of CE to evaluate the interaction between beta2-glycoprotein I (b2gpI) and a number of anionic ligands to contribute to the elucidation of the structure-function relationship of b2gpI. b2gpI is a plasma protein which is involved in the blood coagulation cascade under normal, physiological conditions, however, its precise function is undefined. It is also involved in pathological conditions such as the so-called anti-phospholipid syndrome, where anti-b2gpI autoantibodies induce a prothrombotic state. Therefore, functional characterization of b2gpI under near physiological conditions is of interest. To avoid charge-dependent analyte adsorption to the inner surface of the capillary wall, we have utilized the pH hysteresis effect, where an acidic pretreatment of the capillary made it possible to perform subsequent CE analyses of b2gpI at neutral pH. The interaction between b2gpI and the anionic ligand heparin was studied with migration shift ACE, where the ionic strength, temperature and conformation of b2gpI were easily varied. The interaction between b2gpI and phosphatidylcholine/phosphatidylserine liposomes are subject to an ongoing investigation by means of migration shift ACE, frontal analysis CE, partial filling CE and pre-equilibration partial filling ACE. We conclude that differential, but relatively low binding affinities that are highly dependent on electrostatic interactions and on a preserved conformation of the protein, characterize its interactions with ligands that in vivo will be present in multiple copies on e.g. cell surfaces. The CE procedure for this study is simple, fast and automatic and quantitative binding affinity parameters are conveniently obtained using small amounts of biological materials.
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| 13. |
- Fagerquist, Mats A, et al.
(författare)
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Derivations that enable the testing of fetal urine production as a method of fetal surveillance.
- 2010
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Ingår i: Archives of gynecology and obstetrics. - : Springer Science and Business Media LLC. - 1432-0711 .- 0932-0067. ; 282:5, s. 481-6
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Tidskriftsartikel (refereegranskat)abstract
- To calculate the measurement error of the hourly fetal urine production rate (HFUPR) and evaluate the implication of different methods for measuring the HFUPR, i.e. ellipsoid versus sum-of-cylinders method.
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| 14. |
- Sundberg, Torbjörn, et al.
(författare)
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Reconstruction of propagating Kelvin-Helmholtz vortices at Mercury's magnetopause
- 2011
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 59:15, s. 2051-2057
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Tidskriftsartikel (refereegranskat)abstract
- A series of quasi-periodic magnetopause crossings were recorded by the MESSENGER spacecraft during its third flyby of Mercury on 29 September 2009, likely caused by a train of propagating Kelvin-Helmholtz (KH) vortices. We here revisit the observations to study the internal structure of the waves. Exploiting MESSENGER's rapid traversal of the magnetopause, we show that the observations permit a reconstruction of the structure of a rolled-up KH vortex directly from the spacecraft's magnetic field measurements. The derived geometry is consistent with all large-scale fluctuations in the magnetic field data, establishes the non-linear nature of the waves, and shows their vortex-like structure. In several of the wave passages, a reduction in magnetic field strength is observed in the middle of the wave, which is characteristic of rolled-up vortices and is related to the increase in magnetic pressure required to balance the centrifugal force on the plasma in the outer regions of a vortex, previously reported in computer simulations. As the KH wave starts to roll up, the reconstructed geometry suggests that the vortices develop two gradual transition regions in the magnetic field, possibly related to the mixing of magnetosheath and magnetospheric plasma, situated at the leading edges from the perspectives of both the magnetosphere and the magnetosheath.
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| 15. |
- Sundberg, Torbjörn, et al.
(författare)
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The Kelvin-Helmholtz instability at Mercury : An assessment
- 2010
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 58:11, s. 1434-1441
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Tidskriftsartikel (refereegranskat)abstract
- The Kelvin-Helmholtz instability is believed to be an important means for the transfer of energy, plasma, and momentum from the solar wind into planetary magnetospheres, with in situ measurements reported from Earth, Saturn, and Venus. During the first MESSENGER flyby of Mercury, three periodic rotations were observed in the magnetic field data possibly related to a Kelvin-Helmholtz wave on the dusk side magnetopause. We present an analysis of the event, along with comparisons to previous Kelvin-Helmholtz observations and an investigation of what influence finite ion gyro radius effects, believed to be of importance in the Hermean magnetosphere, may have on the instability. The wave signature does not correspond to that of typical Kelvin-Helmholtz events, and the magnetopause direction does not show any signs of major deviation from the unperturbed case. There is thus no indication of any high amplitude surface waves. On the other hand, the wave period corresponds to that expected for a Kelvin-Helmholtz wave, and as the dusk side is shown to be more stable than the dawn side, we judge the observed waves not to be fully developed Kelvin-Helmholtz waves, but they may be an initial perturbation that could cause Kelvin-Helmholtz waves further down the tail. (C) 2010 Elsevier Ltd. All rights reserved.
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