Comparison of the molecular weight distribution of gelatin fractions by size-exclusion chromatography and light scattering

Commercial gelatin is a heterogeneous proteinaceous product with a broad range of molecular weights. The use of gelatin to prepare insoluble nanoparticles depends largely on the presence of high molecular weight fractions that can be separated by size-exclusion chromatography. The purpose of this study was to determine the molecular fractions of gelatins from three commercial types (B225, B60 and A60), measure their molecular weight and compare these with data obtained from an absolute light scattering method. The mean molecular weight of the gelatins decreased in the order B225 > B60 > A60. All samples were polydisperse, with fractions varying from 2 MDa. Each sample was divided into eight fractions based on the molecular weight distribution and using a paired t-test the two methods were shown to be in substantial agreement. The light scattering method would appear to provide an absolute quality control procedure for commercial gelatin, depending on its application and requirements.peer-reviewe

The non-linear evolution of magnetic flux ropes: 3. effects of dissipation

International audienceWe study the evolution (expansion or oscillation) of cylindrically symmetric magnetic flux ropes when the energy dissipation is due to a drag force proportional to the product of the plasma density and the radial speed of expansion. The problem is reduced to a single, second-order, ordinary differential equation for a damped, non-linear oscillator. Motivated by recent work on the interplanetary medium and the solar corona, we consider polytropes whose index, ?, may be less than unity. Numerical analysis shows that, in contrast to the small-amplitude case, large-amplitude oscillations are quasi-periodic with frequencies substantially higher than those of undamped oscillators. The asymptotic behaviour described by the momentum equation is determined by a balance between the drag force and the gradient of the gas pressure, leading to a velocity of expansion of the flux rope which may be expressed as (1/2?)r/t, where r is the radial coordinate and t is the time. In the absence of a drag force, we found in earlier work that the evolution depends both on the polytropic index and on a dimensionless parameter, ?. Parameter ? was found to have a critical value above which oscillations are impossible, and below which they can exist only for energies less than a certain energy threshold. In the presence of a drag force, the concept of a critical ? remains valid, and when ? is above critical, the oscillatory mode disappears altogether. Furthermore, critical ? remains dependent only on ? and is, in particular, independent of the normalized drag coefficient, ?*. Below critical ?, however, the energy required for the flux rope to escape to infinity depends not only on ? (as in the conservative force case) but also on ?*. This work indicates how under certain conditions a small change in the viscous drag coefficient or the initial energy may alter the evolution drastically. It is thus important to determine ?* and ? from observations

The 293 K structure of tetradehydrohaliclonacyclamine A

The polycyclic title compound {systematic name: (1S,16S,17S,31S)-3,20- diaza-tetra-cyclo-[15.15.0.1.1] tetra-tria-conta-6,8,23,25-tetra-ene}, CHN , has recently been isolated and characterized structurally, in solution by NMR spectroscopy and in the solid state by X-ray crystallography. At 130 K the structure is monoclinic (P21, Z = 4) and comprises two mol-ecules in the asymmetric unit with distinctly different conformations in the twelve-C-atom bridging chains. We report that, at 250 K, a phase change from monoclinic to ortho-rhom-bic (P22121, Z = 4) occurs. The higher-temperature phase is structurally characterized herein at 293 K. The two different conformers resolved in the monoclinic low-temperature form merge to give a single disordered mol-ecule in the asymmetric unit of the high-temperature phase

Observational aspects of IMF draping-related magnetosheath accelerations for northward IMF

Acceleration of magnetosheath plasma resulting from the draping of the interplanetary magnetic field (IMF) around the magnetosphere can give rise to flow speeds that exceed that of the solar wind (VSW) by up to ~60%. Three case event studies out of 34 identified events are described. We then present a statistical study of draping-related accelerations in the magnetosheath. Further, we compare the results with the recent theory of Erkaev et al. (2011, 2012). We present a methodology to help distinguish draping-related accelerations from those caused by magnetic reconnection. To rule out magnetopause reconnection at low latitudes, we focus mainly on the positive Bz phase during the passage of interplanetary coronal mass ejections (ICMEs), as tabulated in Richardson and Cane (2010) for 1997–2009, and adding other events from 2010. To avoid effects of high-latitude reconnection poleward of the cusp, we also consider spacecraft observations made at low magnetic latitudes. We study the effect of upstream Alfvén Mach number (MA) and magnetic local time (MLT) on the speed ratio V/VSW. The comparison with theory is good. Namely, (i) flow speed ratios above unity occur behind the dawn–dusk terminator, (ii) those below unity occur on the dayside magnetosheath, and (iii) there is a good general agreement in the dependence of the V ratio on MA

Combined Multipoint Remote and In Situ Observations of the Asymmetric Evolution of a Fast Solar Coronal Mass Ejection

We present an analysis of the fast coronal mass ejection (CME) of 2012 March 7, which was imaged by both STEREO spacecraft and observed in situ by MESSENGER, Venus Express, Wind and Mars Express. Based on detected arrivals at four different positions in interplanetary space, it was possible to strongly constrain the kinematics and the shape of the ejection. Using the white-light heliospheric imagery from STEREO-A and B, we derived two different kinematical profiles for the CME by applying the novel constrained self-similar expansion method. In addition, we used a drag-based model to investigate the influence of the ambient solar wind on the CME's propagation. We found that two preceding CMEs heading in different directions disturbed the overall shape of the CME and influenced its propagation behavior. While the Venus-directed segment underwent a gradual deceleration (from ~2700 km/s at 15 R_sun to ~1500 km/s at 154 R_sun), the Earth-directed part showed an abrupt retardation below 35 R_sun (from ~1700 to ~900 km/s). After that, it was propagating with a quasi-constant speed in the wake of a preceding event. Our results highlight the importance of studies concerning the unequal evolution of CMEs. Forecasting can only be improved if conditions in the solar wind are properly taken into account and if attention is also paid to large events preceding the one being studied

Heliospheric Evolution of Magnetic Clouds

Interplanetary evolution of eleven magnetic clouds (MCs) recorded by at least two radially aligned spacecraft is studied. The in situ magnetic field measurements are fitted to a cylindrically symmetric Gold-Hoyle force-free uniform-twist flux-rope configuration. The analysis reveals that in a statistical sense the expansion of studied MCs is compatible with self-similar behavior. However, individual events expose a large scatter of expansion rates, ranging from very weak to very strong expansion. Individually, only four events show an expansion rate compatible with the isotropic self-similar expansion. The results indicate that the expansion has to be much stronger when MCs are still close to the Sun than in the studied 0.47 - 4.8 AU distance range. The evolution of the magnetic field strength shows a large deviation from the behavior expected for the case of an isotropic self-similar expansion. In the statistical sense, as well as in most of the individual events, the inferred magnetic field decreases much slower than expected. Only three events show a behavior compatible with a self-similar expansion. There is also a discrepancy between the magnetic field decrease and the increase of the MC size, indicating that magnetic reconnection and geometrical deformations play a significant role in the MC evolution. About half of the events show a decay of the electric current as expected for the self-similar expansion. Statistically, the inferred axial magnetic flux is broadly consistent with it remaining constant. However, events characterized by large magnetic flux show a clear tendency of decreasing flux.Comment: 64 pages, 10 figure

Accelerated magnetosheath flows caused by IMF draping: Dependence on latitude

In previous work we used a semi-analytical treatment to describe accelerated magnetosheath flows caused by the draping of interplanetary magnetic field (IMF) lines around the magnetosphere. Here, we use the same approach, i.e., modeling the magnetic field lines as elastic strings, to examine how the magnetic tension force, one of the two agents responsible for producing these flows, varies along field lines away from the equatorial plane. The bend in the field line caused by the draping mechanism propagates as two oppositely-directed waves to higher latitudes. For a due northward IMF - the case we consider here - these propagate symmetrically north/south of the equatorial plane. As a result, a two-peaked latitude velocity profile develops as we go further downtail and the velocity peaks migrate along the magnetic field line to higher latitudes. We examine this velocity-profile for two Alfvén Mach numbers (MA = 8 and 3), representative of conditions in the solar wind at 1 AU (“normal” solar wind and solar transients). Qualitatively, the picture is the same but quantitatively there are important differences: (i) the flows reach higher values for the lower MA (maximum V/VSW = 1.6) than for the higher MA (V/VSW= 1.3); (ii) asymptotic values are reached farther downstream of the dawn-dusk terminator for the lowerMA (∼−50 RE vs −15 RE); (iii) For the lower MAthe highest speeds are reached away from the equatorial plane. We predict two channels of fast magnetosheath flow next to the magnetopause at off-equatorial latitudes that exceed the solar wind speed

The role of magnetic handedness in magnetic cloud propagation

We investigate the propagation of magnetic clouds (MCs) through the inner heliosphere using 2.5-D ideal magnetohydrodynamic (MHD) simulations. A numerical solution is obtained on a spherical grid, either in a meridional plane or in an equatorial plane, by using a Roe-type approximate Riemann solver in the frame of a finite volume approach. The structured background solar wind is simulated for a solar activity minimum phase. In the frame of MC propagation, special emphasis is placed on the role of the initial magnetic handedness of the MC\u27s force-free magnetic field because this parameter strongly influences the efficiency of magnetic reconnection between the MC\u27s magnetic field and the interplanetary magnetic field. Magnetic clouds with an axis oriented perpendicular to the equatorial plane develop into an elliptic shape, and the ellipse drifts into azimuthal direction. A new feature seen in our simulations is an additional tilt of the ellipse with respect to the direction of propagation as a direct consequence of magnetic reconnection. During propagation in a meridional plane, the initial circular cross section develops a concave-outward shape. Depending on the initial handedness, the cloud\u27s magnetic field may reconnect along its backside flanks to the ambient interplanetary magnetic field (IMF), thereby losing magnetic flux to the IMF. Such a process in combination with a structured ambient solar wind has never been analyzed in detail before. Furthermore, we address the topics of force-free magnetic field conservation and the development of equatorward flows ahead of a concave-outward shaped MC. Detailed profiles are presented for the radial evolution of magnetoplasma and geometrical parameters. The principal features seen in our MHD simulations are in good agreement with in-situ measurements performed by spacecraft. The 2.5-D studies presented here may serve as a basis under more simple geometrical conditions to understand more complicated effects seen in 3-D simulations

Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections

Space weather refers to dynamic conditions on the Sun and in the space environment of the Earth, which are often driven by solar eruptions and their subsequent interplanetary disturbances. It has been unclear how an extreme space weather storm forms and how severe it can be. Here we report and investigate an extreme event with multi-point remote-sensing and in-situ observations. The formation of the extreme storm showed striking novel features. We suggest that the in-transit interaction between two closely launched coronal mass ejections resulted in the extreme enhancement of the ejecta magnetic field observed near 1 AU at STEREO A. The fast transit to STEREO A (in only 18.6 hours), or the unusually weak deceleration of the event, was caused by the preconditioning of the upstream solar wind by an earlier solar eruption. These results provide a new view crucial to solar physics and space weather as to how an extreme space weather event can arise from a combination of solar eruptions.Comment: 23 pages, 7 figure