Supersaturated dispersions of rod-like viruses with added attraction

The kinetics of isotropic-nematic (I-N) and nematic-isotropic (N-I) phase transitions in dispersions of rod-like {\it fd}-viruses are studied. Concentration quenches were applied using pressure jumps in combination with polarization microscopy, birefringence and turbidity measurements. The full biphasic region could be accessed, resulting in the construction of a first experimental analogue of the bifurcation diagram. The N-I spinodal points for dispersions of rods with varying concentrations of depletion agents (dextran) were obtained from orientation quenches, using cessation of shear flow in combination with small angle light scattering. We found that the location of the N-I spinodal point is independent of the attraction, which was confirmed by theoretical calculations. Surprisingly, the experiments showed that also the absolute induction time, the critical nucleus and the growth rate are insensitive of the attraction, when the concentration is scaled to the distance to the phase boundaries.Comment: 13 pages, 14 figures. accepted in Phsical Review

An analytical approach to converting vibration signal to combustion characteristics of homogeneous charge compression ignition engines

Homogeneous charge compression ignition (HCCI) is a promising low-temperature combustion technique for low-emission internal combustion engines. Unlike conventional engines, HCCI lacks a direct ignition control mechanism, necessitating closed-loop combustion control. This study proposes a phenomenological-based, cost-effective, and non-intrusive approach using vibration data analysis to determine essential combustion parameters. Experiments were conducted on a single-cylinder research engine with an accelerometer attached to the engine head. The engine operation envelope covered the whole engine’s operating area in naturally aspirated HCCI mode. Wavelet analysis revealed that combustion-related frequencies centered around 500 Hz, independent of operating conditions. The correlation-seeking analysis included peak acceleration amplitude and its crank angle with peak heat release rate (HRR) data. The peak HRR location was accurately identified within one degree when vibration amplitude exceeded the 100 m/s2 threshold. This encompassed 98.5% of the analyzed combustion cycles. The peak HRR prediction accuracy had a maximum error below 21% and was suitable to monitor reaction rates, especially in incomplete combustion and high ringing cycles.© 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).fi=vertaisarvioitu|en=peerReviewed

An analytical approach to converting vibration signal to combustion characteristics of homogeneous charge compression ignition engines

Abstract Homogeneous charge compression ignition (HCCI) is a promising low-temperature combustion technique for low-emission internal combustion engines. Unlike conventional engines, HCCI lacks a direct ignition control mechanism, necessitating closed-loop combustion control. This study proposes a phenomenological-based, cost-effective, and non-intrusive approach using vibration data analysis to determine essential combustion parameters. Experiments were conducted on a single-cylinder research engine with an accelerometer attached to the engine head. The engine operation envelope covered the whole engine’s operating area in naturally aspirated HCCI mode. Wavelet analysis revealed that combustion-related frequencies centered around 500 Hz, independent of operating conditions. The correlation-seeking analysis included peak acceleration amplitude and its crank angle with peak heat release rate (HRR) data. The peak HRR location was accurately identified within one degree when vibration amplitude exceeded the 100 m/s2 threshold. This encompassed 98.5% of the analyzed combustion cycles. The peak HRR prediction accuracy had a maximum error below 21% and was suitable to monitor reaction rates, especially in incomplete combustion and high ringing cycles

Peculiar Disorder in Molecular Crystals of 9,10-Dimethyltriptycene. A Single-Crystal ¹H NMR Study

Former single-crystal and powder X-ray diffraction studies of 9,10-dimethyltriptycene (<b>1</b>) and its isotopomer-<i>d</i>₁₂ selectively deuterated in the aromatic positions (<b>1a</b>) consistently delivered undistorted <i>R</i>3̅<i>c</i> structure of the material. On the other hand, ¹H wide line NMR spectra of polycrystalline <b>1a</b> reported by us previously were incompatible with the above structure. The presently reported ¹H spectra of a single crystal of <b>1a</b> shed new light onto these discrepancies. These spectra reveal two sharply defined environments of the methyl groups in the investigated crystal, of which only one is consistent with the <i>R</i>3̅<i>c</i> structure. In it, the methyl groups from neighboring molecules come as closely spaced pairs of <i>D</i>_3<i>d</i> symmetry, coupled by intermolecular proton–proton dipole interactions. The other environment encompasses as much as about 20% of the methyl groups. They also appear to fit the <i>R</i>3̅<i>c</i> lattice but, at variance with those occurring in pairs, do not show dipole couplings to their neighbors. Despite these differences, both sorts of the methyl groups show the same thermally activated dynamics, what was confirmed by line shape fits to variable temperature spectra of the investigated crystal. The diverse properties with respect to intermolecular dipolar couplings cannot be explained in terms of a static disorder, with the isolated groups facing voids in the lattice. This interpretation is untenable because no sufficient deficit in the crystal’s specific weight was observed. Moreover, no foreign electron density, possibly originated from solvent molecules occluded in the crystal voids, could be detected in the X-ray studies. The fact that some sort of disorder occurs in the investigated crystals is indicated by the presence of diffuse scattering features in the X-ray data. A tentative explanation of these observations in terms of a dynamic disorder of a hitherto unreported type is proposed. It calls for further intense research to elucidate connections between diffuse scattering of X-rays and possible types of disorder in molecular van der Waals crystals of organic compounds

Time domain para hydrogen induced polarization

Para hydrogen induced polarization (PHIP) is a powerful hyperpolarization technique, which increases the NMR sensitivity by several orders of magnitude. However the hyperpolarized signal is created as an anti-phase signal, which necessitates high magnetic field homogeneity and spectral resolution in the conventional PHIP schemes. This hampers the application of PHIP enhancement in many fields, as for example in food science, materials science or MRI, where low B0-fields or low B0-homogeneity do decrease spectral resolution, leading to potential extinction if in-phase and anti-phase hyperpolarization signals cannot be resolved. Herein, we demonstrate that the echo sequence (45°-t-180°-t) enables the acquisition of low resolution PHIP enhanced liquid state NMR signals of phenylpropiolic acid derivatives and phenylacetylene at a low cost low-resolution 0.54 T spectrometer. As low field TD-spectrometers are commonly used in industry or biomedicine for the relaxometry of oil–water mixtures, food, nano-particles, or other systems, we compare two variants of para-hydrogen induced polarization with data-evaluation in the time domain (TD-PHIP). In both TD-ALTADENA and the TD-PASADENA strong spin echoes could be detected under conditions when usually no anti-phase signals can be measured due to the lack of resolution. The results suggest that the time-domain detection of PHIP-enhanced signals opens up new application areas for low-field PHIP-hyperpolarization, such as non-invasive compound detection or new contrast agents and biomarkers in low-field Magnetic Resonance Imaging (MRI). Finally, solid-state NMR calculations are presented, which show that the solid echo (90y-t-90x-t) version of the TD-ALTADENA experiment is able to convert up to 10% of the PHIP signal into visible magnetization

Application of Parahydrogen-Induced Polarization to Unprotected Dehydroamino Carboxylic Acids

One focus of current nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) investigation is the hyperpolarization of biologically relevant substrates. In this study, the application of parahydrogen-induced polarization (PHIP) to amino carboxylic acids was enabled by protonation of the amino group as well as of the carboxylic acid. Due to the donor character of these functional groups, they usually act as ligands at the active catalytic sites. To enable parahydrogenation, blocking of the catalytic sites by the functional groups has to be avoided. In a new approach, this was realized via protonation of the starting material. For the first time PHIP spectra of allylglycine, vigabatrin and gamma-amino-butyric acid (GABA) were generated. The feasibility of the hydrogenation of amino carboxylic acids without using a protection group supersedes the deprotection reaction usually required. Hence, hydrogenation after protonation of the substrate opens the class of free dehydroamino carboxylic acids to PHIP

Understanding the leaching properties of heterogenized catalysts: A combined solid-state and PHIP NMR study

Para-hydrogen induced polarization (PHIP) NMR in solution, combined with solid-state NMR, can be efficiently employed for the highly sensitive in-situ detection of the leaching properties of immobilized catalysts. The knowledge of this property is important for possible applications of PHIP experiments in medicine, biology or industry, where leached catalysts poison the solution of hyperpolarized products. As experimental example Wilkinson's catalyst RhCl(PPh3)(3) (1) immobilized on mesoporous silica is chosen. As model reaction the hydrogenation of styrene in solvents with different polarities (methanol-d(4), acetone-d(6) and benzene-d(6)) is used. A P-31 solid-state MAS-NMR study reveals that there are two different species of catalysts on the silica, namely coordinatively bound catalysts and physisorbed catalyst. Only the second species exhibits substantial leaching, which is visible in a strong PHIP enhancement of the reaction product. (C) 2011 Elsevier Inc. All rights reserved