Synthesis of High χ–Low N Diblock Copolymers by Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) enables the scalable synthesis of functional block copolymer nanoparticles with various morphologies. Herein we exploit this versatile technique to produce so-called “high χ–low N” diblock copolymers that undergo nanoscale phase separation in the solid state to produce sub-10 nm surface features. By varying the degree of polymerization of the stabilizer and core-forming blocks, PISA provides rapid access to a wide range of diblock copolymers, and enables fundamental thermodynamic parameters to be determined. In addition, the pre-organization of copolymer chains within sterically-stabilized nanoparticles that occurs during PISA leads to enhanced phase separation relative to that achieved using solution-cast molecularly-dissolved copolymer chains.     

Metric Boolean algebras and constructive measure theory

 This work concerns constructive aspects of measure theory. By considering metric completions of Boolean algebras – an approach first suggested by Kolmogorov – one can give a very simple construction of e.g. the Lebesgue measure on the unit interval. The integration spaces of Bishop and Cheng turn out to give examples of such Boolean algebras. We analyse next the notion of Borel subsets. We show that the algebra of such subsets can be characterised in a pointfree and constructive way by an initiality condition. We then use our work to define in a purely inductive way the measure of Borel subsets. Received: 9 November 2000 / Revised version: 23 March 2001 / Published online: 12 July 2002     

Temperature and wavelength dependent trap filling in M2Si5N8:Eu (M=Ca,Sr, Ba) persistent phosphors

The evaluation of persistent phosphors is often focused on the processes right after the excitation, namely on the shape of the afterglow decay curve and the duration of the afterglow, in combination with thermoluminescence glow curve analysis. In this paper we study in detail the trap filling process in europium-doped alkaline earth silicon nitrides (Ca₂Si₅N₈:Eu, Sr₂Si₅N₈:Eu and Ba₂Si₅N₈:Eu), i.e., how the persistent luminescence can be induced. Both the temperature at which the phosphors are excited and the spectral distribution of the excitation light on the ability to store energy in the phosphors' lattices are investigated. We show that for these phosphors this storage process is thermally activated upon excitation in the lower 5d excited states of Eu²⁺, with the lowest thermal barrier for europium doped Ca₂Si₅N₈. Also, the influence of co-doping with thulium on the trap filling and afterglow behavior is studied. Finally there exists a clear relation between the luminescence quenching temperature and the trap filling efficiency. The latter relation can be utilized to select new efficient 5d–4f based afterglow phosphors.     

The saturation scale and its x-dependence from Λ polarization studies

The transverse polarization of forward Λ   hyperons produced in high-energy p–A$p\text{–}A$ collisions is expected to display an extremum at a transverse momentum around the saturation scale. This was first observed within the context of the McLerran–Venugopalan model which has an x  -independent saturation scale. The extremum arises due to the kt$k_t$-odd nature of the polarization-dependent fragmentation function, which probes approximately the derivative of the dipole scattering amplitude. The amplitude changes most strongly around the saturation scale, resulting in a peak in the polarization. We find that the observation also extends to the more realistic case in which the saturation scale Qs$Q_s$ is x-dependent. Since a range of x   and therefore Qs$Q_s$ values is probed at a given transverse momentum and rapidity, this result is a priori not expected. Moreover, the measurement of Λ   polarization over a range of xF$x_F$ values actually provides a direct probe of the x-dependence of the saturation scale. This novel feature is demonstrated for typical LHC kinematics and for several phenomenological models of the dipole scattering amplitude. We show that although the measurement will be challenging, it may be feasible at LHC. The situation at RHIC is not favorable, because the peak will likely be at too low transverse momentum of the Λ to be a trustworthy measure of the saturation scale.     

Rotational CARS N2 thermometry: validation experiments for the influence of nitrogen spectral line broadening by hydrogen

Rotational coherent anti‐Stokes Raman spectroscopy (CARS) in fuel‐rich hydrocarbon flames, with a large content of hydrogen in the product gases (∼20%), has in previous work shown that evaluated temperatures are raised several tens of Kelvin by taking newly derived N₂ H₂ Raman line widths into account. To validate these results, in this work calibrated temperature measurements at around 300, 500 and 700 K were performed in a cell with binary gas mixtures of nitrogen and hydrogen. The temperature evaluation was made with respect to Raman line widths either from self‐broadened nitrogen only, N₂ N₂ [energy‐corrected‐sudden (ECS)], or by also taking nitrogen broadened by hydrogen, N₂ H₂ [Robert–Bonamy (RB)], Raman line widths into account. With increased amount of hydrogen in the cell at constant temperature, the evaluated CARS temperatures were clearly lowered with the use of Raman line widths from self‐broadened nitrogen only, and the case with inclusion of N₂ H₂ Raman line widths was more successful. The difference in evaluated temperatures between the two different sets increases approximately linearly, reaching 20 K (at T ∼ 300 K), 43 K (at T = 500 K) and 61 K (at T = 700 K) at the highest hydrogen concentration (90%). The results from this work further emphasize the importance of using adequate Raman line widths for accurate rotational CARS thermometry. Copyright © 2010 John Wiley & Sons, Ltd.     

Embedding some Riemann surfaces into $${\mathbb {C}^2}$$ with interpolation

We prove that several types of open Riemann surfaces, including the finitely connected planar domains, embed properly into such that the values on any given discrete sequence can be arbitrarily prescribed. Kutzschebauch supported by Schweizerische Nationalfonds grant 200021-107477/1.     

Speciation and legislation – Where are we today and what do we need for tomorrow?

In international legislation concerning trace elements in food, in the environment or in occupational health most regulations are based on the total element contents, and are frequently given as maximum limits or guideline levels. In contrast, only few regulations pay attention to the molecular species in which the elements are bound. The international legislation concerning contaminants in food is presently being established in the Codex Alimentarius, which is an independent United Nations organisation under the joint FAO/WHO Food Standards Programme. Development of the Codex General Standard for Contaminants and Toxins in Food provides the framework for future international legislation on metals as contaminants in food. For certain food additives, which include some essential minerals, speciation is an integral part of the set of specification criteria, because only certain defined chemical compounds are permitted as sources of the essential element. The development of more species-specific analytical and toxicological data, and improved communication with legislators will be necessary before it will become possible to lay down species-specific regulations in all the cases where the specialised scientist will consider it reasonable.     

Total synthesis of calystegine A7

A straightforward chiral pool synthesis for the glycosidase inhibitor calystegine A₇ (isolated from Lycium chinense) from methyl α-d-glucopyranoside is described. Keysteps of this synthesis include a ultrasound assisted Zn-mediated tandem ring opening reaction followed by a Grubbs' catalyst mediated ring closure metathesis.