Flow Separation and Turbulence in Jet Pumps for Thermoacoustic Applications

The effect of flow separation and turbulence on the performance of a jet pump in oscillatory flows is investigated. A jet pump is a static device whose shape induces asymmetric hydrodynamic end effects when placed in an oscillatory flow. This will result in a time-averaged pressure drop which can be used to suppress acoustic streaming in closed-loop thermoacoustic devices. An experimental setup is used to measure the time-averaged pressure drop as well as the acoustic power dissipation across two different jet pump geometries in a pure oscillatory flow. The results are compared against published numerical results where flow separation was found to have a negative effect on the jet pump performance in a laminar flow. Using hot-wire anemometry the onset of flow separation is determined experimentally and the applicability of a critical Reynolds number for oscillatory pipe flows is confirmed for jet pump applications. It is found that turbulence can lead to a reduction of flow separation and hence, to an improvement in jet pump performance compared to laminar oscillatory flows.     

Spatial Coherence of the Heat Release Fluctuations in Turbulent Jet and Swirl Flames

The noise generation of turbulent flames is governed by temporal changes of the total flame volume due to local heat release fluctuations. On the basis of the wave equation an expression for the relationship between the acoustic power and the heat release fluctuations is derived and a correlation function is obtained which reveals that the sound pressure level of flames is governed by the spatial coherence. Noise models rely on precise coherence information in terms of characteristic length scales, which are the measure of the acoustic efficiency of the flame. Since the published length scale information is scarce and inconsistent, length scales were measured for a number of laboratory flames using two measurement techniques developed for this purpose: A planar LIF-system with a repetition rate of 1 kHz acquires the instantaneous flame front position and heat release, whereas two chemiluminescence probes with an optics confining the measurement volume to a line of sight provide further spatial correlation data. For all flames investigated the length scales are smaller than the height of the burner exit annulus and they are of the order of the local flame brush thickness. Using the measured length scales, the coherent volume and the efficiency of the noise generation are calculated, which are three orders of magnitude higher than measured. However, the proper order of magnitude is obtained, if only the measured fluctuating part of the thermal power is used in the model and if the periodic formation of local zones with heat release overshoot and deficit are properly incorporated.     

Affinity purification of viral protein having heterogeneous quaternary structure: Modeling the impact of soluble aggregates on chromatographic performance

Prokaryote-expressed polyomavirus structural protein VP1 with an N-terminal glutathione-S-transferase tag (GST-VP1) self-assembles into pentamer structures that further organize into soluble aggregates of variable size (3.4 × 10²–1.8 × 10⁴ kDa) [D.I. Lipin, L.H.L. Lua, A.P.J. Middelberg, J. Chromatogr. A 1190 (2008) 204]. The adsorption mechanism for the full range of GST-VP1 soluble aggregates was described assuming a dual-component model [T.Y. Gu, G.J. Tsai, G.T. Tsao, AICHE J. 37 (1991) 1333], with components differentiated by size, and hence pore accessibility, rather than by protein identity. GST-VP1 protein was separated into two component groups: aggregates small enough to access resin pores (LMW: 3.4 × 10²–1.4 × 10³ kDa) and aggregates excluded from the resin pores (HMW: 9.0 × 10²–1.8 × 10⁴ kDa). LMW aggregates bound to resin at a higher saturation concentration (29.7 g L⁻¹) than HMW aggregates (13.3 g L⁻¹), while the rate of adsorption of HMW aggregates was an order of magnitude higher than for LMW aggregates. The model was used to predict both batch and packed bed adsorption of GST-VP1 protein in solutions with known concentrations of HMW and LMW aggregates to Glutathione Sepharose HP resin. Asymmetrical flow field flow fractionation with UV absorbance was utilized in conjunction with adsorption experimentation to show that binding of HMW aggregates to the resin was strong enough to withstand model-predicted displacement by LMW aggregates. High pore concentrations of LMW aggregates were also found to significantly inhibit the diffusion rate of further protein in the resin pores. Additional downstream processing experimentation showed that enzymatic cleavage of LMW aggregates to remove GST tags yields more un-aggregated VP1 pentamers than enzymatic cleavage of HMW aggregates. This model can be used to enhance the chromatographic capture of GST-VP1, and suggests an approach for modeling chromatographic purification of proteins that have a range of quaternary structures, including soluble aggregates.     

A prime geodesic theorem for SL<Subscript>4</Subscript>

A prime geodesic theorem is derived for rank-one geodesics in quotients of SL₄. This has applications in class number asymptotics for quartic fields. For these applications it is necessary to prove a more general statement than in the literature: several regularity conditions have to be abandoned. As a consequence, the analytical difficulties multiply. The final result is obtained by a sandwiching argument from infinitely many independent asymptotics.     

ESR-Untersuchungen zur Struktur der 1,2-Thiazet-yle,einer Neuen Klasse Stabiler Radikale

The structures of benzo[c] and naphtho [2,1-c]-1,2-thiazet- yl have been elucidated by ESR spectroscopy (including simulation of the spectra and investigation of the corresponding ¹⁵N- and N-D-compounds) and by mass spectroscopic studies. This new class of stable S,N-radicals, available from different starting materials, belongs to an oxygen-free type of N-radical.     

Exact spin rotation by precession during neutron interferometry

Time dependent magnetic fields can be used to produce exact rotations of spin wavefunctions. This avoids the inherent approximations encountered in experiments performed with static fields to demonstrate the effect of 2π-rotations on fermions. Two of the experiments proposed explicitly will use forthcoming interferometers for ultra cold neutrons.