Dampfkesselbetrieb

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The origin of the bistability in the thiazyl radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA): A first principles bottom-up investigation of the magnetic properties of its high temperature polymorph

A first principles bottom-up study is performed on the high temperature polymorph of the thiazyl radical 1,3,5-trithia-2,4,6-triazapentalenyl, TTTA, a purely organic molecule-based magnet that shows thermal bistability, with the aim of getting a quantitative understanding at the molecular level the mechanism of thermal bistability and the factors that control the existence of a hysteresis loop. Experimental studies on crystals of TTTA have shown that it is a thermally bistable material that exhibits a broad hysteresis loop encompassing room temperature (the high temperature phase is paramagnetic, while the low temperature phase is magnetically silent). Both structures present 1D π-stacks and the changes in the magnetic properties up to now have been solely attributed to changes within these stacks, which in the high temperature phase are composed of evenly-spaced radicals and in the low temperature phase the radicals are separated by alternately long and short spacings. Our study shows that the magnetic topology of the high temperature polymorph is clearly 3D with important interactions between the stacks, however a 1D magnetic model gives a qualitative reproduction of the macroscopic magnetic properties. This suggests that a proper investigation into the origin of the bistability of this material requires consideration of the inter-stack interactions as well as looking at the difference in packing within the stacks.     

Die Trennung des Kupfers vom Cadmium

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Top-down protein sequencing by CID and ECD using desorption electrospray ionisation (DESI) and high-field FTICR mass spectrometry

We report high resolution spectra for the medium molecular weight proteins myoglobin and cytochrome-c obtained using a custom desorption electrospray ionisation (DESI) source coupled to a Bruker Daltonics 12 T Apex Qe Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS). The DESI source was designed for accurate alignment and reproduction of critical geometric variables. A two axis motorised stage was included to enable automated rastering of the sample under the DESI plume. Spectra for the intact proteins have been obtained under single-acquisition conditions and a top-down analysis of cytochrome-c was performed using both collision induced dissociation (CID) and electron capture dissociation (ECD) of the isolated [M+15H]¹⁵⁺ charge state. The sequence coverage is comparable to that obtained using electrospray ionisation, demonstrating the utility of top-down protein analysis by DESI FTICR-MS.     

NMR studies into colloidal stability and magnetic order in fatty acid stabilised aqueous magnetic fluids

We report the physico-chemical characterisation of fatty acid stabilised aqueous magnetic fluids, which are ideal systems for studying the influence of nanoparticle aggregation on the emergent magnetic resonance properties of the suspensions. Stable colloids of superparamagnetic magnetite, Fe(3)O(4), nanoparticle clusters in the 80 to 100 nm size range were produced by in situ nanoparticle growth and stabilisation, and by suspending pre-formed nanoparticles. NMR relaxation analysis shows that the magnetic resonance properties of the two types of suspension differ substantially and provides new insights into how the relaxation mechanisms are determined by the organisation of the nanoparticles within the clusters.     

A Note on the Cops and Robber Game on Graphs Embedded in Non-Orientable Surfaces

We consider the two-player, complete information game of Cops and Robber played on undirected, finite, reflexive graphs. A number of cops and one robber are positioned on vertices and take turns in sliding along edges. The cops win if, after a move, a cop and the robber are on the same vertex. The minimum number of cops needed to catch the robber on a graph is called the cop number of that graph. Let c(g) be the supremum over all cop numbers of graphs embeddable in a closed orientable surface of genus g, and likewise ${\tilde c(g)}$ for non-orientable surfaces. It is known (Andreae, 1986) that, for a fixed surface, the maximum over all cop numbers of graphs embeddable in this surface is finite. More precisely, Quilliot (1985) showed that c(g) ≤ 2g + 3, and Schröder (2001) sharpened this to ${c(g)\le \frac32g + 3}$ . In his paper, Andreae gave the bound ${\tilde c(g) \in O(g)}$ with a weak constant, and posed the question whether a stronger bound can be obtained. Nowakowski & Schröder (1997) obtained ${\tilde c(g) \le 2g+1}$ . In this short note, we show ${\tilde c(g) \leq c(g-1)}$ , for any g ≥ 1. As a corollary, using Schröder’s results, we obtain the following: the maximum cop number of graphs embeddable in the projective plane is 3, the maximum cop number of graphs embeddable in the Klein Bottle is at most 4, ${\tilde c(3) \le 5}$ , and ${\tilde c(g) \le \frac32g + 3/2}$ for all other g.     

Ueber die constanten Fehler bei Atomgewichtsbestimmungen

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MANAGEMENT OF A RENEWABLE RESOURCE WITH A FINITE DEMAND ELASTICITY

Optimal management policies are derived for a renewable resource when the demand for output has finite elasticity. The analysis modifies traditional views of this problem by allowing for the possibility that static optimizing policies, which maximize myopic net revenues, may be superior to “Golden Rule” policies which account for longer-run stock effects.