Turbulence Plus

This paper attempts to give a concise overview of the turbulence research performed at the Laboratory for Aero and Hydrodynamics of the Delft University of Technology under the guidance of Frans Nieuwstadt. Frans Nieuwstadt was appointed in 1986 as director of the laboratory, and he held this position until his sudden death in 2005. Frans’ principal interest was to investigate turbulence at a fundamental level, but also to consider turbulence and its role in other processes. He coined a name for this research: turbulence plus.     

The Effect of Oxandrolone on Voice Frequency in Growth Hormone-Treated Girls With Turner Syndrome

Objectives/Hypothesis

Oxandrolone (Ox) increases height gain but may also cause voice deepening in growth hormone (GH)-treated girls with Turner syndrome (TS). We assessed the effect of Ox on objective and subjective speaking voice frequency in GH-treated girls with TS.

Study Design

A multicenter, randomized, placebo (Pl)-controlled, double-blind study was conducted.

Methods

One hundred thirty-three patients were included and treated with GH (1.33 mg/m²/d) from baseline, combined with Pl or Ox in a low (0.03 mg/kg/d) or conventional (0.06 mg/kg/d) dose from the age of 8 years and estrogens from the age of 12 years. Yearly from starting Ox/Pl until 6 months after discontinuing GH + Ox/Pl, voices were recorded and questionnaires were completed.

Results

At start, mean (±standard deviation [SD]) voice frequency SD score (SDS) was high for age (1.0 ± 1.2, P < 0.001) but normal for height. Compared with GH + Pl, voices tended to lower on GH + Ox 0.03 (P = 0.09) and significantly lowered on GH + Ox 0.06 (P = 0.007). At the last measurement, voice frequency SDS was still relatively high in GH + Pl group (0.6 ± 0.7, P = 0.002) but similar to healthy girls in both GH + Ox groups. Voice frequency became lower than −2 SDS in one patient (3%) on GH + Ox 0.03 and three patients (11%) on GH + Ox 0.06. The percentage of patients reporting subjective voice deepening was similar between the dosage groups.

Conclusions

Untreated girls with TS have relatively high-pitched voices. The addition of Ox to GH decreases voice frequency in a dose-dependent way. Although most voice frequencies remain within the normal range, they may occasionally become lower than −2 SDS, especially on GH + Ox 0.06 mg/kg/d.     

Evaluation of diverse α/β-backbone patterns for functional α-helix mimicry: analogues of the Bim BH3 domain

Peptidic oligomers that contain both α- and β-amino acid residues, in regular patterns throughout the backbone, are emerging as structural mimics of α-helix-forming conventional peptides (composed exclusively of α-amino acid residues). Here we describe a comprehensive evaluation of diverse α/β-peptide homologues of the Bim BH3 domain in terms of their ability to bind to the BH3-recognition sites on two partner proteins, Bcl-x(L) and Mcl-1. These proteins are members of the anti-apoptotic Bcl-2 family, and both bind tightly to the Bim BH3 domain itself. All α/β-peptide homologues retain the side-chain sequence of the Bim BH3 domain, but each homologue contains periodic α-residue → β(3)-residue substitutions. Previous work has shown that the ααβαααβ pattern, which aligns the β(3)-residues in a 'stripe' along one side of the helix, can support functional α-helix mimicry, and the results reported here strengthen this conclusion. The present study provides the first evaluation of functional mimicry by ααβ and αααβ patterns, which cause the β(3)-residues to spiral around the helix periphery. We find that the αααβ pattern can support effective mimicry of the Bim BH3 domain, as manifested by the crystal structure of an α/β-peptide bound to Bcl-x(L), affinity for a variety of Bcl-2 family proteins, and induction of apoptotic signaling in mouse embryonic fibroblast extracts. The best αααβ homologue shows substantial protection from proteolytic degradation relative to the Bim BH3 α-peptide.     

Experiments on the Flow Field and Acoustic Properties of a Mach number 0·75 Turbulent Air Jet at a Low Reynolds Number

In this paper we present the experimental results of a detailed investigation of the flow and acoustic properties of a turbulent jet with Mach number 0·75 and Reynolds number 3·5 10³. We describe the methods and experimental procedures followed during the measurements, and subsequently present the flow field and acoustic field. The experiment presented here is designed to provide accurate and reliable data for validation of Direct Numerical Simulations of the same flow. Mean Mach number surveys provide detailed information on the centreline mean Mach number distribution, radial development of the mean Mach number and the evolution of the jet mixing layer thickness both downstream and in the early stages of jet development. Exit conditions are documented by measuring the mean Mach number profile immediately above the nozzle exit. The fluctuating flow field is characterised by means of a hot-wire, which produced radial profiles of axial turbulence at several stations along the jet axis and the development of flow fluctuations through the jet mixing layer. The axial growth rate of the jet instabilities are determined as function of Strouhal number, and the axial development of several spectral components is documented. The directivity of the overall sound pressure level and several spectral components were investigated. The spectral content of the acoustic far field is shown to be compatible with findings of hot-wire experiments in the mixing layer of the jet. In addition, the measured acoustic spectra agree with Tam’s large-scale similarity and fine-scale similarity spectra (Tam et al., AIAA Pap 96, 1996).     

Phase diagrams of CuCl2·2NC5H5 and CsCuCl3

The phase diagrams of two quasi one-dimensional,$\text{S =}\text{1}\text{2}$ quantum systems CuCl₂·2NC₅H₅ and CsCuCl₃, have been determined experimentally for fields between 0 and 90 kOe. The results show an increase of the Néel temperature as a function of the field, in accordance with earlier observations on manganese systems.     

Load and depth sensing indentation as a tool to monitor a gradient in the mechanical properties across a polymer coating: A study of physical and chemical aging effects

Load and depth sensing indentation has been used to characterize the elastic modulus and hardness of various polycarbonate films. This analytical technique is shown to be extremely suitable for the determination of gradients in these mechanical properties. Furthermore, it is demonstrated that such a gradient exists over a length of micrometers in chemically aged polycarbonate, but it is virtually absent in physically aged polycarbonate. From these results, it is concluded that, although the first 100 nm cannot be probed, physical aging occurs homogeneously throughout the bulk of the sample. However, chemical aging starts at the surface and moves progressively into the bulk of the material. From the study of these films, it appears that for the interpretation of these measurements, knowledge about the amount of creep occurring during the measurements and about the mechanical properties of the substrate on which these films are applied is needed. Creep can be measured with the same indenter through the application of a constant load for a period of time. Load and depth sensing indentation appears to be a powerful method for studying the physical and chemical aging of polymers. It is especially valuable for coatings and films for which conventional tensile testing is problematic. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1628–1639, 2004     

Photoresponsive molecular tools for emerging applications of light in medicine

Light-based therapeutic and imaging modalities, which emerge in clinical applications, rely on molecular tools, such as photocleavable protecting groups and photoswitches that respond to photonic stimulus and translate it into a biological effect. However, optimisation of their key parameters (activation wavelength, band separation, fatigue resistance and half-life) is necessary to enable application in the medical field. In this perspective, we describe the applications scenarios that can be envisioned in clinical practice and then we use those scenarios to explain the necessary properties that the photoresponsive tools used to control biological function should possess, highlighted by examples from medical imaging, drug delivery and photopharmacology. We then present how the (photo)chemical parameters are currently being optimized and an outlook is given on pharmacological aspects (toxicity, solubility, and stability) of light-responsive molecules. With these interdisciplinary insights, we aim to inspire the future directions for the development of photocontrolled tools that will empower clinical applications of light.

This perspective article explores the current state of light-controlled molecular tools for medical therapy and imaging and offers an outlook on clinical application scenarios and optimisation strategies.     

DNA-based asymmetric catalysis: sequence-dependent rate acceleration and enantioselectivity

This study shows that the role of DNA in the DNA-based enantioselective Diels-Alder reaction of azachalcone with cyclopentadiene is not limited to that of a chiral scaffold. DNA in combination with the copper complex of 4,4'-dimethyl-2,2'-bipyridine (Cu-L1) gives rise to a rate acceleration of up to 2 orders of magnitude compared to Cu-L1 catalysis alone. Furthermore, both the enantioselectivity and the rate enhancement prove to be dependent on the DNA-sequence. These features are the main reasons for the efficient and enantioselective catalysis observed with salmon testes DNA/Cu-L1 in the Diels-Alder reaction. The fact that absolute levels of stereocontrol can be achieved with a simple and weak DNA-binding complex like Cu-L1 is a clear demonstration of the power of the supramolecular approach to hybrid catalysis.