Refractive-index and density matching in concentrated particle suspensions: a review

Optical measurement techniques such as particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) are now routinely used in experimental fluid mechanics to investigate pure fluids or dilute suspensions. For highly concentrated particle suspensions, material turbidity has long been a substantial impediment to these techniques, which explains why they have been scarcely used so far. A renewed interest has emerged with the development of specific methods combining the use of iso-index suspensions and imaging techniques. This review paper gives a broad overview of recent advances in visualization techniques suited to concentrated particle suspensions. In particular, we show how classic methods such as PIV, LDV, particle tracking velocimetry, and laser induced fluorescence can be adapted to deal with concentrated particle suspensions.     

Spektralphotometrische Untersuchungen zur Lichtwirkung auf das Silberkeimsol

Zusammenfassung Einleitende qualitative Versuche haben bewiesen, da\ die Entf?rbungsreaktion der nach der Keimmethode hergestellten Silberhydrosole ganz wahrscheinlich ein Oxydationsvorgang des kolloiden Silbers unter Wirkung des Wasserstoffperoxyds ist, welches sich unter dem Einflu\ der ultravioletten Strahlen im Dispersionsmittel (Wasser) bildet. Quantitative, spektralphotometrische Untersuchungen haben bewiesen, da\ wir es in diesem Falle mit einer Reaktion der ersten Ordnung zu tun haben. Der Temperaturkoeffizient dieser Entf?rbungsreaktion ist ziemlich klein, jedoch etwas gr?\er als Eins.     

Anomalous isotopic effect in multibubble sonoluminescence of aqueous solutions of terbium chloride

An anomalously low isotope effect has been discovered in 20-kHz sonoluminescence of terbium chloride solutions in H₂O-D₂O mixtures. The intensity of luminescence in the characteristic 488-and 545-nm lines of the Tb³⁺ ion, which are observed against the solvent continuum (230–700 nm), increases with the content of D₂O to a maximum value of 4.0 ± 0.4, whereas the isotope effect in photoluminescence of the same solutions reaches 10 ± 1.0. The result is explained using the model of nonexponential decay of sonoluminescence of Tb³⁺ ions. These ions, which are formed in an excited state in cavitation bubbles, first undergo radiative and radiationless deactivation in the gas phase. However, some excited ions enter the solution bulk, because the excitation lifetime is longer than the average bubble lifetime. At the first stage, the isotope effect is small, because the density of the gas phase is low and quenching by solvent molecules is weak. At the second stage, the isotope effect coincides with the effect in usual photoluminescence in the solution. The total decrease in the effect in sonoluminescence depends on the weight of the “gas” stage of deactivation of excited Tb³⁺ ions.     

Bubbling in unbounded coflowing liquids

An investigation of the stability of low density and viscosity fluid jets and spouts in unbounded coflowing liquids is presented. A full parametrical analysis from low to high Weber and Reynolds numbers shows that the presence of any fluid of finite density and viscosity inside the hollow jet elicits a transition from an absolute to a convective instability at a finite value of the Weber number, for any value of the Reynolds number. Below that critical value of the Weber number, the absolute character of the instability leads to local breakup, and consequently to local bubbling. Experimental data support our model.     

First-principles investigation of the vibrational properties of 3-tert-butylcyclohexene

I present a first-principles investigation of the vibrational properties of the chiral molecule 3-tert-butylcyclohexene. The vibrational density of states (vDOS) of the two existing conformers has been calculated ab initio within the framework of density-functional theory and density-functional perturbation theory, using both the local-density approximation and the generalized-gradient approximation for the exchange-correlation potential. The vDOS of the two conformers are very similar. The vDOS has been investigated with respect to contributions of the cyclohexene ring and the tert-butyl group and also regarding the localization of vibrational modes. Additionally, the eigendisplacements of characteristic modes of 3-tert-butylcyclohexene have been analyzed.     

Influence of the slow wave on the relation between the angular resonances and the leaky guided modes properties for a poroelastic plate embedded in water

A numerical study of the guided modes in a water-saturated poroelastic plate that obeys the Biot theory is presented. In the first part, we study the leaky guided modes and the angular resonances when the slow wave does not propagate. Two types of guided modes exist. The first ones occur from coupling of the fast longitudinal wave with the shear wave; most of them propagate whatever the frequency is, provided that it is not close to their cut-off frequencies. The leaky guided modes of the second type occur from coupling of the two longitudinal waves and the shear wave. These modes do not propagate (they are highly damped) as long as the slow wave remains diffusive. We show that the characteristics of the angular resonances can be linked to the leaky guided waves of the first type in the same way as for an elastic plate. The guided modes of the second type may not be associated to angular resonances. In the second part, we consider a thinner plate in a higher frequency range so that the slow wave can propagate. Once again its influence is studied both on the leaky guided modes and on the angular resonances.     

Detection of multicomponent signals: effect of difference in level between components

The detection of multicomponent signals for which the components are not equidetectable is precisely investigated as a function of the level difference ΔL(i∕j) between components. The detection thresholds are determined for a seven-tone complex signal with random starting phases masked by white noise. Level differences between the components are examined. A model for non-equidetectable conditions based on the statistical summation model is described. The improvement in detection is calculated from the level difference between components that is related to the thresholds for single components. The model predictions are in accordance with the experimental results.     

Synthesis of branched oxime-linked peptide mimetics of the MUC1 containing a universal T-helper epitope

Our goal was to develop mimics of MUC1, highly immunogenic to induce an efficient immune response against the tumor-associated form of MUC1, and sufficiently different from the natural antigen to bypass the tolerance barrier in humans. With the aim of obtaining a well-defined peptide construct as a means of evoking the precise immune responses required in immunotherapy, we synthesized artificial mimics of the MUC1 protein composed of two MUC1 repeat units of inverse orientation and a universal T-helper epitope. To synthesize these heteromeric peptide constructs, we followed a convergent approach using chemoselective ligation based on oxime chemistry. A stem peptide was first synthesized bearing two orthogonally masked aldehydes. After successive deprotection, two oxime bonds can be specifically generated. The proposed strategy proved to be concise and robust, and allowed the synthesis of the tri-branched protein in a very satisfactory yield. The different constructs were tested for their ability to generate antibodies able to recognize the MUC1 protein.     

Chiral induction in self-assembled helicates: CHIRAGEN type ligands with ferrocene bridging units

The aim of this work was the preparation of enantiomerically pure bis(pinene-bipyridine) ligands containing the ferrocenyl moiety. Several such ligands (1-3) were synthesized and completely characterized. These molecules can be diastereoselectively deprotonated at the acidic methylene group of the pinene moiety using a strong and sterically hindered base such as LDA. Subsequent reaction of the formed anion with alkyl halides yield the family of C(2)-symmetric enantiopure compounds (1a-c). Copper(I), silver(I), or zinc(II) complexes with several ligands (C1-C8) were prepared and structurally characterized in the solid state and in solution. Self-assembled helical species are formed in several cases. It became evident that the chiral groups present in the ligand do not completely determined the helical configuration of the assemblages. Diastereoselectivity is thus not complete with this type of ligands, contrary to other, similar ligands studied before.