Effects of reactor type and mass transfer on the morphology of CuS and ZnS crystals

For the precipitation of CuS and ZnS, the effects of the reactor/precipitator type, mass transfer and process conditions on crystal morphology were studied. Either H₂S gas or a S^2– solution were applied. Three different types of reactors have been tested, namely a laminar jet, a bubble column and an MSMPR reactor. The choice of reactor type as well as mass transfer and metal concentration all have a considerable influence on the morphology of the produced crystals. A well mixed bubble column with H₂S containing gas as feed yields the coarsest crystals. Use is then made of the surface active properties of CuS‐particles, which induce agglomeration at the gas‐liquid interface, where as the low metal concentrations inside the reactor also contribute to the formation of coarser particles (especially for ZnS). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polarization-Free Generators and the S-Matrix

Polarization-free generators, i.e. “interacting” Heisenberg operators which are localized in wedge-shaped regions of Minkowski space and generate single particle states from the vacuum, are a novel tool in the analysis and synthesis of two-dimensional integrable quantum field theories. In the present article, the status of these generators is analyzed in a general setting. It is shown that such operators exist in any theory and in any number of spacetime dimensions. But in more than two dimensions they have rather delicate domain properties in the presence of interaction. If, for example, they are defined and temperate on a translation-invariant, dense domain, then the underlying theory yields only trivial scattering. In two-dimensional theories, these domain properties are consistent with non-trivial interaction, but they exclude particle production. Thus the range of applications of polarization-free generators seems to be limited to the realm of two-dimensional theories. Received: 11 April 2000 / Accepted: 20 April 2000     

Triplet-Induced Lesion Formation at CpT and TpC Sites in DNA

UV irradiation induces DNA lesions particularly at dipyrimidine sites. Using time-resolved UV pump (250 nm) and mid-IR probe spectroscopy the triplet pathway of cyclobutane pyrimidine dimer (CPD) formation within TpC and CpT sequences was studied. The triplet state is initially localized at the thymine base but decays with 30 ns under formation of a biradical state extending over both bases of the dipyrimidine. Subsequently this state either decays back to the electronic ground state on the 100 ns time scale or forms a cyclobutane pyrimidine dimer lesion (CPD). Stationary IR spectroscopy and triplet sensitization via 2′-methoxyacetophenone (2-M) in the UVA range shows that the lesions are formed with an efficiency of approximately 1.5 %. Deamination converts the cytosine moiety of the CPD lesions on the time scale of 10 hours into uracil which gives CPD(UpT) and CPD(TpU) lesions in which the coding potential of the initial cytosine base is vanished.     

NMR Spectroscopy in the Optimization and Evaluation of RAFT Agents

The selection of a suitable mediating agent in Reversible Addition-Fragmentation Chain Transfer (RAFT) mediated polymerization is crucial to the degree of control that can be achieved. An overview of work from the Stellenbosch group is presented in which the use of NMR spectroscopy as a tool for evaluating RAFT-agents is highlighted. The occurrence of selective initialization, i.e. the selective conversion of a RAFT-agent into its single monomer adduct is discussed for various classes of monomers, as well as for copolymerization. One of the general rules for living polymerization is that chains should start growing early in the polymerization reaction. Selective initialization is claimed to be the extreme case where all chains have begun growing after the conversion of only one monomer equivalent per RAFT-agent.     

Unconventional dynamics in triangular Heisenberg antiferromagnet NaCrO2

We report magnetization, specific heat, muon spin rotation, and Na NMR measurements on the S=3/2 rhombohedrally stacked Heisenberg antiferromagnet NaCrO2. This compound appears to be a good candidate for the study of isotropic triangular Heisenberg antiferromagnets with very weak interlayer coupling. While specific heat and magnetization measurements indicate the onset of a transition in the range Tc approximately 40-50 K, both muon spin rotation and NMR reveal a fluctuating crossover regime extending well below Tc, with a peak of relaxation rate T1(-1) around T approximately 25 K. This novel finding is discussed within the context of excitations in the triangular Heisenberg antiferromagnets.     

Causality and Dispersion Relations and the Role of the S-Matrix in the Ongoing Research

The adaptation of the Kramers-Kronig dispersion relations to the causal localization structure of QFT led to an important project in particle physics, the only one with a successful closure. The same cannot be said about the subsequent attempts to formulate particle physics as a pure S-matrix project. The feasibility of a pure S-matrix approach are critically analyzed and their serious shortcomings are highlighted. Whereas the conceptual/mathematical demands of renormalized perturbation theory are modest and misunderstandings could easily be corrected, the correct understanding about the origin of the crossing property requires the use of the mathematical theory of modular localization and its relation to the thermal KMS condition. These new concepts, which combine localization, vacuum polarization and thermal properties under the roof of modular theory, will be explained and their potential use in a new constructive (nonperturbative) approach to QFT will be indicated. The S-matrix still plays a predominant role but, different from Heisenberg’s and Mandelstam’s proposals, the new project is not a pure S-matrix approach. The S-matrix plays a new role as a “relative modular invariant”.     

Easy-axis kagome antiferromagnet: local-probe study of Nd3Ga5SiO14

We report a local-probe investigation of the magnetically anisotropic kagome compound Nd3Ga5SiO14. Our zero-field muon spin relaxation (muSR) results provide direct evidence of a fluctuating collective paramagnetic state down to 60 mK, supported by a wipeout of the Ga nuclear magnetic resonance (NMR) signal below 25 K. At 60 mK a dynamics crossover to a much more static state is observed by muSR in magnetic fields above 0.5 T. Accordingly, the NMR signal is recovered at low T above a threshold field, revealing a rapid temperature and field variation of the magnetic fluctuations.     

Radionuclide tumour therapy with ultrasound contrast microbubbles

Radionuclides have shown to be effective in tumour therapy. However, the side effects determine the maximum deliverable dose. Recently, it has been demonstrated that cells can be permeabilised through sonoporation using ultrasound and contrast microbubbles. The use of sonoporation in treatment of tumours may increase the anti-tumour efficacy of radionuclide treatment. The mechanisms as well as the effects sonoporation in tumour treatment strategies are still not understood. The purpose of this study is to determine the effects of ultrasound and contrast microbubbles on the internalisation of the radionuclide (111)In-DOTA-Tyr(3)-octreotate in tumour cells. To optimize ultrasound settings for ultrasound adjunctive tumour therapy we incubated rat pancreatic CA20948 tumour cells with two dyes (MW 40 and 70 kDa). The uptake levels were compared with cells treated with ultrasound and contrast microbubbles for different ultrasound settings. The highest molecular uptake was found with addition of contrast microbubbles (ratio of 10 bubbles to 1 cell) and with the ultrasound setting: duty cycle 0.013%, mechanical index (MI) 0.42, and treatment times of 30 and 60 min. These settings were used to enhance the internalisation of (111)In-DOTA-Tyr(3)-octreotate. We found a 160% higher internalisation of (111)In-DOTA-Tyr(3)-octreotate by tumour cells adjunctively treated with ultrasound and contrast microbubbles compared to untreated cells. These results show that adjunctive tumour treatment with the radionuclide (111)In-DOTA-Tyr(3)-octreotate and ultrasound contrast microbubbles may be feasible. When using adjunctive ultrasound contrast microbubble treatment, a lower radionuclide doses are required to reach the same anti-tumour effect.     

N Chemical Shift Tensor Magnitude and Orientation in the Molecular Frame of Uracil Determined via MAS NMR

The potential of heteronuclear MAS NMR spectroscopy for the characterization of ¹⁵N chemical shift (CS) tensors in multiply labeled systems has been illustrated, in one of the first studies of this type, by a measurement of the chemical shift tensor magnitude and orientation in the molecular frame for the two ¹⁵N sites of uracil. Employing polycrystalline samples of ¹⁵N₂ and 2-¹³C,¹⁵N₂-labeled uracil, we have measured, via ¹⁵N–¹³C REDOR and ¹⁵N–¹H dipolar-shift experiments, the polar and azimuthal angles (θ, ψ) of orientation of the ¹⁵N–¹³C and ¹⁵N–¹H dipolar vectors in the ¹⁵N CS tensor frame. The (θ_NC, ψ_NC) angles are determined to be (92 ± 10°, 100 ± 5°) and (132 ± 3°, 88 ± 10°) for the N1 and N3 sites, respectively. Similarly, (θ_NH, ψ_NH) are found to be (15 ± 5°, −80 ± 10°) and (15 ± 5°, 90 ± 10°) for the N1 and N3 sites, respectively. These results obtained based only on MAS NMR measurements have been compared with the data reported in the literature.