Letzte Entwicklungen in der Theorie und Praxis der dynamischen analytischen Technik (Continuous Flow Analysis)

Zusammenfassung Während der beiden letzten Jahre hat man versucht, eine theoretische Basis für die dynamische analytische Technik zu entwickeln. Neue Systeme, die auf diesen Überlegungen basieren, sind schon konstruiert und haben bessere Eigenschaften bewiesen. Zwei Systeme, die schon auf dem Markt sind, werden beschrieben. Das erste ist ein Vielfachanalysen-system, das für klinische Routineuntersuchungen vorgesehen ist. Das zweite ist ein neuer vollautomatischer Aminosäurenanalysator, welcher in der Lage ist, Chromatogramme viel schneller als jedes andere existierende Gerät zu produzieren.

---

Latest developments in the theory and practice of continuous flow analysis

In the last few years there has been an increased interest in developing a theoretical basis for continuous flow analysis. These theoretical considerations have lead to the development of improved and simplified analytical systems. Two such systems are already commercially available and are described. The first is a multiple system for the routine clinical examination of blood serum for 12 different parameters. The second is a fully automated chromatographic system for the determination of amino acids in protein hydrolysates and physiological fluids.

     

Bistability and the phase transition in 1,3,2-dithiazolo[4,5-b]pyrazin-2-yl

The molecular radical 1,3,2-dithiazolo[4,5-b]pyrazin-2-yl (PDTA) exhibits magnetic bistability just above room temperature, undergoing a well-defined hysteretic phase change with TC downward arrow = 297(1) K and TC upward arrow = 343(1) K. The crystal structures of the two phases of PDTA have been determined by single-crystal X-ray diffraction at 323(2) K. LT-PDTA consists of diamagnetic (S = 0) nearly superimposed pi-dimer stacks, while that of HT-PDTA comprises slipped stacks of pi-radicals (S = 1/2). The structural interconversion is suggested to proceed via the cooperative breaking and making of intermolecular S- - -N interactions and an inversion symmetry-preserving "domino cascade" of the pi-stacked rings.     

Three-body dissociation dynamics of the low-lying Rydberg states of H3 and D3

The dynamics of the three-body dissociative charge exchange of fast (12 keV) H+3 and D+3 with Cs have been studied using multiparticle translational spectroscopy. The observed partitioning of product momenta was found to be state-specific and yields insights into the nuclear motion during dissociation for the three lowest-lying 2s 2A'1, 2p 2A'2, and 3p 2E' metastable Rydberg states of H3 and the 2s 2A'1 and 2p 2A'2 states for D3. These results provide direct empirical information on the nonadiabatic couplings that govern the three-body dissociation of the lowest-lying Rydberg states of H3 and D3.     

Four-body reaction dynamics: complete correlated fragment measurement of the dissociative photodetachment dynamics of O(-)(8)

The four-body dissociative photodetachment (DPD) dynamics of O-8 were studied using photoelectron photofragment coincidence (PPC) spectroscopy. All four neutral photofragments were measured in coincidence with the photodetached electron, yielding a five-body kinematically complete experiment. Velocity and angular correlations for DPD of O(-)(8) are presented and compared to those for O(-)(6). The DPD dynamics and energetics of O(-)(8).are found to be similar to those of O-4 and O-6 implying that the additional solvating O(2) molecules act essentially as spectators, but exhibit inequivalent kinematic behavior implying asymmetric solvation.     

An electrostatic precipitator system for the Martian environment

Human exploration missions to Mars will require the development of technologies for the utilization of the planet's own resources for the production of commodities. However, the Martian atmosphere contains large amounts of dust. The extraction of commodities from this atmosphere requires prior removal of this dust. We report on our development of an electrostatic precipitator able to collect Martian simulated dust particles in atmospheric conditions approaching those of Mars. Extensive experiments with an initial prototype in a simulated Martian atmosphere showed efficiencies of 99%. The design of a second prototype with aerosolized Martian simulated dust in a flow-through is described.     

First-row transition metal atoms adsorption on rutile TiO2(110) surface

We performed periodic DFT calculations for adsorption of metal atoms on a perfect rutile TiO₂(110) surface (at low coverage, ???=?1/3) to investigate the interaction of an individual metal atom with TiO₂ and to compare it with a study previously done on MgO(100). We considered partial period of Mendeleev??s table from K to Zn. The overall evolution of the adsorption energies shows two maxima as for MgO(100). Two main differences, however, exist: the adsorption energy is much stronger and the first maximum is enhanced relative to the second one. This is attributed to the reducibility of the surface titanium cation. When the adsorbed metal is electropositive, it is oxidized under adsorption transferring electrons to titanium cations. We present the effect of introducing a Hubbard term to the gradient-corrected approximation band-structure Hamiltonian (GGA?+?U). The introduction of a reasonable Hubbard correction preserves the trends and allows localizing the electron of the reduction on Ti atoms in the near surface region. Finally, our results conclude that for heavier M atoms of the period, insertion is energetically favored relative to adsorption.     

Evaluation of a learning trajectory for length in the early years

Measurement is a critical component of mathematics education, but research on the learning and teaching of measurement is limited, especially compared to topics such as number and operations. To contribute to the establishment of a research base for instruction in measurement, we evaluated and refined a previously developed learning trajectory in early length measurement, focusing on the developmental progressions that provide cognitive accounts of the development of children’s strategic and conceptual knowledge of measure. Findings generally supported the developmental progression, in that children reliably moved through the levels of thinking in that progression. For example, they passed through a level in which they measured length by placing multiple units or attempting to iterate a unit, sometimes leaving gaps between units. However, findings also suggested several refinements to the developmental progression, including the nature and placement of indirect length comparison in the developmental progression and the role of vocabulary, which was an important facilitator of learning for some, but not all, children.     

Teaching Length Measurement: Research Challenges

Many publications and curriculum materials promote a specific instructional sequence for introducing length measure: gross comparisons of length, measurement with nonstandard units such as paper clips, measurement with manipulative standard units, and finally measurement with standard instruments such as rulers. Several recent studies, however, imply that aspects of this traditional approach may not match children's developmental progression. This article describes several studies that challenge conventional wisdom regarding the teaching and learning of nonstandard and standard units, rulers, and measurement sense and draws educational implications from their results.     

Additive Macaulay Posets

An additive sequence of integers is a finite sequence in which the sum of any number of consecutive terms is less than or equal to the sum of the same number of initial terms in the sequence and greater than or equal to the sum of the same number of final terms in the sequence. If the final several terms in an additive sequence are greater than or equal to, in order, the initial several terms of a second additive sequence, then the juxtaposition of the two sequences is also additive. This simple fact has combinatorial corollaries.