Interpretation of harmonic structure in solar type II radio bursts

Spectrographic and partly imaging observations of three Type II solar radio bursts displaying three drifting bands with frequencies related as 1¬2¬3 are discussed. The radio data of two of these events were simultaneousely recorded by the digital radiospectrograph of the Observatory of Solar Radioastronomy in Potsdam-Tremsdorf and the radioheliograph of the Paris-Meudon Observatory in Nançay. The data allow the brightness temperatures of radio emission in the three frequency bands to be determined. The second harmonic is traditionally explained as a result of coalescence of two plasma waves into an electromagnetic wave at twice the plasma frequency. Two nonlinear merging processes—the coalescence of three plasma waves, and of a plasma wave and an electromagnetic wave at twice the plasma frequency—are considered to explain the occurrence of the third harmonic on Type II dynamic spectra. The analysis shows that both processes can fit the observed brightness temperatures of the second and third harmonic. The first process acts preferably at low phase velocities of plasma waves and sharp electron density gradients in the source, and the second process dominates in the case of high plasma wave phase velocities. It is shown that the occurrence of the third harmonic in type II bursts due to nonlinear processes in the coronal plasma indicates not only a powerful event but also some specific conditions in the shock or foreshock region. Finally, we propose a method to distinguish between the two invoked nonlinear processes by a statistical investigation of Type II burst data.     

Efficiency of electron acceleration by shock waves in the solar corona according to observational data on the fine structure of type II radio bursts

Herringbone bursts (HB-bursts) are the type III-like fine structure in type II bursts of solar radio emission and are usually interpreted as plasma radiation arising from fast electrons accelerated by shock waves in the solar corona. In general outline, the radiation mechanism of HB-bursts is similar to that of type III bursts. However, HB-bursts have brightness temperatures that are about an order of magnitude higher than those of type III bursts. The frequency drift of BH-bursts is about two or three times lower than that for type III bursts. All this shows that the fast-electron beams responsible for HB-bursts and type III bursts differ markedly in their parameters. We calculated expected brightness temperatures of HB-bursts at the fundamental and second harmonic and compared our results with Culgoora radiometer and radioheliograph data and Tremsdorf spectrograph data in order to estimate parameters of fast-electron beams generating HB-bursts. We found that the observed brightness temperatures of HB-bursts give velocities of fast electrons accelerated by shock waves within the limits (0.02–0.17)c. These velocities are several times lower than those for type III bursts (0.15–0.5)c. The density of the fast electrons responsible for HB-bursts is in the interval 3·10⁻⁶ <n_b/n<6·10⁻⁵, which exceeds by 1–2 orders of magnitude the relative densities in type III sources. This gives a clue to understanding the markedly higher brightness temperatures of HB-bursts compared to those of type III bursts. We concluded that the parameters obtained for the agent exciting HB-bursts favor of turbulence mechanisms of electron acceleration by shock waves in the solar corona. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia; Astrophysical Institute, Potsdam, Germany. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 2, pp. 164–176, February, 1998.     

Control of surface topography in biomimetic calcium phosphate coatings

The behavior of cells responsible for bone formation, osseointegration, and bone bonding in vivo are governed by both the surface chemistry and topography of scaffold matrices. Bone-like apatite coatings represent a promising method to improve the osteoconductivity and bonding of synthetic scaffold materials to mineralized tissues for regenerative procedures in orthopedics and dentistry. Polycaprolactone (PCL) films were coated with calcium phosphates (CaP) by incubation in simulated body fluid (SBF). We investigated the effect of SBF ion concentration and soaking time on the surface properties of the resulting apatite coatings. CaP coatings were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), and energy dispersive X-ray spectrometry (EDX). Young's modulus (E(s)) was determined by nanoindentation, and surface roughness was assessed by atomic force microscopy (AFM) and mechanical stylus profilometry. CaP such as carbonate-substituted apatite were deposited onto PCL films. SEM and AFM images of the apatite coatings revealed an increase in topographical complexity and surface roughness with increasing ion concentration of SBF solutions. Young's moduli (E(s)) of various CaP coatings were not significantly different, regardless of the CaP phase or surface roughness. Thus, SBF with high ion concentrations may be used to coat synthetic polymers with CaP layers of different surface topography and roughness to improve the osteoconductivity and bone-bonding ability of the scaffold.     

Carbohydrate–Lipid Interactions: Affinities of Methylmannose Polysaccharides for Lipids in Aqueous Solution

The interactions between 3‐O‐methyl‐mannose polysaccharides (MMPs), extracted from Mycobacterium smegmatis (consisting of a mixture of MMP‐10, ‐11, ‐12 and ‐13) or obtained by chemical synthesis (MMP‐5_s, ‐8_s, ‐11_s and ‐14_s), and linear saturated and unsaturated fatty acids (FAs), and a commercial mixture of naphthenic acids (NAs) in aqueous solution at 25 °C and pH 8.5 were quantified by electrospray ionization mass spectrometry (ESI‐MS). Association constants (K_a) for MMP binding to four FAs (myristic acid, palmitic acid, stearic acid and trans‐parinaric acid) were measured by using an indirect ESI‐MS assay, the “proxy protein” method. The K_a values are in the 10⁴–10⁵ M ^?1 range and, based on results obtained for the binding of the synthetic MMPs with palmitic acid, increase with the size of the carbohydrate. Notably, the measured affinity of the extracted MMPs for trans‐parinaric acid is two orders of magnitude smaller than the reported value, which was determined by using a fluorescence assay. Using a newly developed competitive binding assay, referred to as the “proxy protein/proxy ligand” ESI‐MS method, it was shown that MMPs bind specifically to NAs in aqueous solution, with apparent affinities of approximately (5×10⁴) M ^?1 for the mixture of NAs tested. This represents the first demonstration that MMPs can bind to hydrophobic species more complex than those containing linear alkyl/alkenyl chains. Moreover, the approach developed here represents a novel method for probing carbohydrate–lipid interactions.     

Deuterium kinetic isotope effects on the dissociation of a protein-fatty acid complex in the gas phase

Deuterium kinetic isotope effects (KIEs) are reported for the first time for the dissociation of a protein-ligand complex in the gas phase. Temperature-dependent rate constants were measured for the loss of neutral ligand from the deprotonated ions of the 1:1 complex of bovine β-lactoglobulin (Lg) and palmitic acid (PA), (Lg + PA)(n-) → Lg(n-) + PA, at the 6- and 7- charge states. At 25 °C, partial or complete deuteration of the acyl chain of PA results in a measurable inverse KIE for both charge states. The magnitude of the KIEs is temperature dependent, and Arrhenius analysis of the rate constants reveals that deuteration of PA results in a decrease in activation energy. In contrast, there is no measurable deuterium KIE for the dissociation of the (Lg + PA) complex in aqueous solution at pH 8. Deuterium KIEs were calculated using conventional transition-state theory with an assumption of a late dissociative transition state (TS), in which the ligand is free of the binding pocket. The vibrational frequencies of deuterated and non-deuterated PA in the gas phase and in various solvents (n-hexane, 1-chlorohexane, acetone, and water) were established computationally. The KIEs calculated from the corresponding differences in zero-point energies account qualitatively for the observation of an inverse KIE but do not account for the magnitude of the KIEs nor their temperature dependence. It is proposed that the dissociation of the (Lg + PA) complex in aqueous solution also proceeds through a late TS in which the acyl chain is extensively hydrated such that there is no significant differential change in the vibrational frequencies along the reaction coordinate and, consequently, no significant KIE.     

The Influence of Incompressibility on the Microstructure of Dielectric Elastomers

Dielectric elastomers (DE's) are considered in recent times for the development of so called smart actuators. This relatively soft material is deformed under the influence of an external electric field. It is an ideal candidate for application in which complex surface deformations are desired. To increase the deformation range the insertion of material inclusions seems to be a good alternative. In the current work a mixed three field formulation in proposed to handle the quasi incompressibility of DE's for numerical simulations. A numerical analysis is performed in which the mixed formulation is compared with a standard displacement formulation. The results show the importance of the consideration of the nearly incompressible behaviour for the case of heterogeneous DE's. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Approaching Solar Maximum 24 with STEREO—Multipoint Observations of Solar Energetic Particle Events

Since the beginning of the Solar Terrestrial Relations Observatory (STEREO) mission at the end of 2006, the two spacecraft have now separated by more than 130 ^° degrees from the Earth. A 360-degree view of the Sun has been possible since February 2011, providing multipoint in situ and remote sensing observations of unprecedented quality. Combining STEREO observations with near-Earth measurements allows the study of solar energetic particle (SEP) events over a wide longitudinal range with minimal radial gradient effects. This contribution provides an overview of recent results obtained by the STEREO/IMPACT team in combination with observations by the ACE and SOHO spacecraft. We focus especially on multi-spacecraft investigations of SEP events. The large longitudinal spread of electron and ³He-rich events as well as unusual anisotropies will be presented and discussed.     

Numerical modelling and optimization aspects of soft dielectric actuators

Dielectric elastomer actuators (DEAs) represent a new type of actuator made of electroactive polymers which can undergo large deformations. Some applications for DEAs are: Artificial muscles, haptic feedback, pumps, robotics, deformable surfaces in aerospace, etc. For this reason the numerical modelling and optimization of DEAs represent an active field of research which supports the designing process of these actuators. In this work the basic equations of the electro-mechanic coupled problem are presented in a first step. Here the Neo-Hooke and the Yeoh model have been chosen to model the behaviour of a nearly incompressible elastomer. To study optimization aspects, material inclusions in a sandwich type DEA structure have been taken into consideration. Ceramics whit high electric permittivity and air are taken into account to explore the effect of inclusions on the deformation. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Retention of bioactive ligand conformation in a gaseous protein-trisaccharide complex

Arrhenius parameters, obtained with the blackbody infrared radiative dissociation technique, are reported for the dissociation of gaseous protonated complexes of a single-chain variable fragment (scFv) of the monoclonal antibody Se155-4 with structurally constrained trisaccharide ligands that resemble the bioactive conformer. The similarity in the dissociation activation energies measured for the +10 charge-state complexes of the constrained ligands and the native trisaccharide is evidence that the bioactive conformation of the native ligand is retained in the gas phase.     

Bioactive recognition sites may not be energetically preferred in protein-carbohydrate complexes in the gas phase

Arrhenius parameters, obtained with the blackbody infrared radiative dissociation technique, are reported for the dissociation of a gaseous protonated complex of an antibody single chain fragment and its native trisaccharide antigen originating from nonspecific interactions during the nanoelectrospray process. It is shown that the nonspecific complex is kinetically more stable and, at the +10 charge state, energetically more stable than the corresponding specific complex originating from interactions in solution. This is the first demonstration that a bioactive recognition site is not energetically preferred in a protein-ligand complex in the gas phase.