High-amplitude single-mode perturbation evolution at the Richtmyer-Meshkov instability

The single-mode Richtmyer-Meshkov hydrodynamic instability at light/heavy (air/SF6 and air/CO2), close density (air/N2), and heavy/light (air/He) interfaces has been experimentally studied for a low incident shock wave Mach number. Two identical 2D half sinusoidal initial perturbations, with a relatively high initial amplitude, were considered in order to rapidly reach the nonlinear regime and check the reduction of the initial growth rate compared to that predicted by the small-amplitude theory. The growth rate measurements for the air/SF6 and air/CO2 cases are in excellent agreement with the nonlinear model of Sadot et al. coupled with a reduction factor suggested by Rikanati et al. In the air/N2 case, the reversal phase can be precisely described by the linear theory. Finally, the heavy/light experiment is well described by the Vandenboomgaerde model also coupled with a smaller reduction factor.     

Hot-wire method for measurements of turbulent mixing induced by Richtmyer-Meshkov instability in shock tube

A constant temperature hot-wire anemometry method is applied to the study of mixing zones induced by the interaction of a shock wave with Mach number 1.25 in air with air/helium (heavy/light), air/argon or air/krypton (light/heavy) initially plane interfaces. The single wire gauge is positioned at various locations along the shock tube axis. At the present stage of our investigation, although the analysis of the hot-wire signal is not achieved yet, we report the interesting concept of using hot-wire anemometry as a diagnostic method for shock tube studies of the Richtmyer-Meshkov instability. Based on this preliminary work, we discuss prospective experimental signal conversion, in order to provide some new results for this field of investigation, in particular for resolving characteristics of the turbulent mixing zone which is of most interest. Received 3 August 2000 / Accepted 15 February 2001     

Measurement of GEp/GMp via polarization transfer at Q2 = 0.4 GeV /c2

The polarization transfer from longitudinally polarized electrons to protons in the elastic scattering p( e, e' p) has been measured around Q² = 0.4 (GeV/c)² with the three-spectrometer facility at the Mainz microtron MAMI. From this polarization transfer the ratio G _Ep/(G _Mp/μ_p) has been determined. The ratio is found to be slightly less than unity in agreement with recent results from other laboratories and from the Rosenbluth separation of cross-sections measured with unpolarized electrons. Received: 26 July 2001 / Accepted: 25 September 2001     

A DNA aptamer as a new target-specific chiral selector for HPLC

In this paper, a DNA aptamer, known to bind stereospecifically the D-enantiomer of an oligopeptide, i.e., arginine-vasopressin, was immobilized on a chromatographic support. The influence of various parameters (such as column temperature, eluent pH, and salt concentration) on the L- and D-peptide retention was investigated in order to provide information about the binding mechanism and then to define the utilization conditions of the aptamer column. The results suggest that dehydration at the binding interface, charge-charge interactions, and adaptive conformational transitions contribute to the specific D-peptide-aptamer complex formation. A very significant enantioselectivity was obtained in the optimal binding conditions, the D-peptide being strongly retained by the column while the L-peptide eluted in the void volume. A rapid baseline separation of peptide enantiomers was also achieved by modulating the elution conditions. Furthermore, it was established that the aptamer column was stable during an extended period of time. This work indicates that DNA aptamers, specifically selected against an enantiomer, could soon become very attractive as new target-specific chiral selectors for HPLC.     

Salt effects on the interaction of an amphiphilic model molecule with immobilized phosphatidylcholine monolayers

The retention of hydrocortisone (used as an amphiphilic model solute) on an immobilized artificial membrane (IAM) column was investigated in relation to the mobile phase concentration of three sodium salts (representing different rankings in the Hofmeister series, i.e. perchlorate, chloride and sulfate) in order to provide insight into the nature of the solute interactions with phospholipid monolayers. The influence of the salt series on solute retention was found to follow the Hofmeister series, emphasizing the role of hydrophobic effect in the solute retention mechanism on phospholipid monolayers. Retention models based on the extended Wyman relations (preferential interaction theory) were developed to analyze more quantitatively the salt effects on the hydrocortisone retention factor. This analysis as well as additional thermodynamic study suggested that the hydrocortisone binding to IAM involved both an insertion into the hydrophobic inside governed by hydrophobic effects and contacts with the interfacial region implying interactions such as van der Waals interactions/hydrogen bonds between the solute hydroxyl groups and the polar headgroups of phospholipidmonolayers.     

Stabilization of beta-hairpin peptides by salt bridges: role of preorganization in the energetic contribution of weak interactions

A model beta-hairpin peptide has been used to investigate the context-dependent contribution of cross-strand Lys-Glu interactions to hairpin stability. We have mutated two Ser-Lys interstrand pairs to Glu-Lys salt bridges, one close to the type I' Asn-Gly turn sequence (Ser6 --> Glu), and one close to the N- and C-termini (Ser15 --> Glu). Each individual interaction contributes approximately 1.2-1.3 kJ mol(-1) to stability; however, introducing the two salt bridges simultaneously produces a much larger overall contribution (-3.6 kJ mol(-1)) consistent with an important role for preorganization and cooperativity in determining the energetics of weak interactions. We compare and contrast CD and NMR data on the highly folded hairpin with the two Glu-Lys pairs to shed light on the nature of the folded state in water. We show that large cosolvent-induced changes in the CD spectrum, in contrast with the modest effects observed on Halpha chemical shifts, support a hydrophobically collapsed entropy-driven conformation in water whose stability is modulated by long-range Coulombic interactions from the Glu-Lys interactions. Cosolvent stabilizes the structure enthalpically, as is evident from CD melting profiles.     

Correction to: Arterial Wall Stiffening in Caveolin-1 Deficiency-Induced Pulmonary Artery Hypertension in Mice

Experimental Mechanics - The original article was updated to include the missing section from eq. (4) to eq. (8).