Jump relations for shocks in an anisotropic magnetized plasma

The jump relations for shocks moving into a collision-free anisotropic magnetized plasma are investigated under the assumption of isotropy of the plasma behind the shock front. The plasma ahead of the shock is assumed to be stable against the fire-hose instability and the mirror instability. In order to facilitate comparison with the work of Bazer and Ericson on isotropic shocks our nomenclature has been adapted to theirs. It turns out that as in the case of isotropic shocks the density ratio can be at most four corresponding to γ=5/3, that the change in magnetic field is bounded and that except for the case of Alfvén shocks the transverse parts of the magnetic field are collinear. It is further shown that the influence of the anisotropy is greatest for nearly equal thermal and magnetic energy densities. In the case of negative anisotropy no compressive shocks are possible with a major decrease in magnetic field if the thermal energy density much exceeds the magnetic energy density. A new kind of shock is shown to result from the analysis, the major effect of which is to destroy the anisotropy with only small changes in density, magnetic field and velocity vector. Its propagation speed is unbounded. Furthermore it has turned out that compressive, magnetic field increasing shocks have lower bounds in the density jump and magnetic field change for negative and positive anisotropy, respectively. In the collision-free case no unique entropy condition depending only on the total pressure components and densities can be given before the solution of the problem of shock structure. Therefore even expansive shocks may be admissible. The applicability of the isotropy assumption and ad-hoc-assumptions of other authors are briefly discussed.     

Synthesis and structure of K+ [iPrN=C=P]-, a 1-aza-3lambda3-phospha-3-allenide

2-Isopropyl(trimethylsilyl)amino-1lambda3-phosphaalkyne 1 reacts with potassium tert-butoxide to form potassium 1-isopropyl-1-aza-3lambda3-phospha-3-allenide (2). This compound was structurally characterized as the corresponding 18-crown-6 ether complex 3. The molecular structure of 1 was also determined in order to compare the bonding situation in the anion and the neutral lambda3-phosphaalkyne. Compound 3 contains a nitrogen-carbon-phosphorus group for which the parameters were shown by X-ray structural analysis and quantum chemical calculations to lie between the extrema N-C[triple bond]P and N=C=P, suggesting reactivity typical of an ambident anion. This is indeed the case, as subsequent reaction of 2 with chlorotrimethylsilane at nitrogen regenerates the lambda3-phosphaalkyne 1; with chlorotriphenylsilane the new derivative 4 is formed. In contrast, chlorotrimethylstannane reacts at phosphorus, giving the 1-aza-3lambda3-phosphaallene isopropyliminomethylidene(trimethylstannyl)phosphane 5.     

Complex magnetic ordering as a driving mechanism of multifunctional properties of Heusler alloys from first principles

First-principles calculations are used to study the structural, electronic and magnetic properties of (Pd, Pt)-Mn-Ni-(Ga, In, Sn, Sb) alloys, which display multifunctional properties like the magnetic shape-memory, magnetocaloric and exchange bias effect. The ab initio calculations give a basic understanding of the underlying physics which is associated with the complex magnetic behavior arising from competing ferro- and antiferromagnetic interactions with increasing number of Mn excess atoms in the unit cell. This information allows to optimize, for example, the magnetocaloric effect by using the strong influence of compositional changes on the magnetic interactions. Thermodynamic properties can be calculated by using the ab initio magnetic exchange parameters in finite-temperature Monte Carlo simulations. We present guidelines of how to improve the functional properties. For Pt-Ni-Mn-Ga alloys, a shape memory effect with 14% strain can be achieved in an external magnetic field.     

En route to zirconium hydrazides(2-)

The structures and properties of a series of new zirconium hydrazido(1-) complexes and the possibility of converting them to the respective hydrazido(2-) species are reported. Reaction of complex [Zr(N2TBSNpy)Cl2] (1) with the monolithiated hydrazide LiNHNMe2 gave the hydrazido(1-) complex [Zr(N2TBSNpy)(NHNMe2)Cl] (2) which exists as two isomeric forms (2a and 2b) in solution. All attempts to convert a mixture of 2a and 2b to the respective hydrazido(2-) compound by reaction with the bulky base lithium hexamethyldisilazide or via the alkyl/hydrazido(1-) complex [Zr(N2TBSNpy)(CH2SiMe3)(NHNMe2)] (3) and subsequent thermal alkane elimination failed. Reaction of 1 with LiHNNPhMe gave a mixture of stereoisomers of [Zr(N2TBSNpy)(NHNMePh)Cl] (4a and 4b), in which the hydrazido unit is end-on bound in solution and eta 2-bonded in the solid state. Reaction of this mixture with lithium hexamethyldisilazide in the presence of pyridine selectively yielded the hydrazido(2-) complex [Zr(N2TBSNpy)(NNPhMe)(py)] (5) which aggregated upon attempts to isolate it. Reaction of the insoluble precipitate with 4-dimethylaminopyridine (dmap) selectively gave the corresponding hydrazido(2-) complex [Zr(N2TBSNpy)(NNPhMe)(dmap)] (6), which could be obtained in a one-pot reaction directly from 1 and which was analytically and spectroscopically fully characterized. It appears that the isolation of stable hydrazido(2-) complexes of zirconium depends on the type of substituents at the N beta atom as well as the co-ligands coordinated to the metal centre.     

A potential high-throughput method for the determination of lipase activity by potentiometric flow injection titrations

Potentiometric FIA titrations were performed to determine enzyme activities of lipase type B from Candida antarctica, CAL-B. Two substrates, triacetin and tributyrin were hydrolyzed in phosphate buffer solutions, and the concentration change of the base component of the buffer was titrated in a carrier solution containing hydrochloric acid and potassium chloride. The system was calibrated with butyric acid and acetic acid, respectively. FIA titration peaks were evaluated with respect to peak height and peak area. Butyric acid and acetic acid could be titrated in the buffer solution from 3 × 10⁻³ mol L⁻¹ to 0.1 mol L⁻¹. The detection limit of enzyme activity was determined to be 0.07 U mL⁻¹ (15 min reaction time) and the minimum activity was calculated to be 0.035 units corresponding to 35 nmol min⁻¹. The specific activities of lipase B for the hydrolysis of tributyrin and triacetin were determined as 16 ± 2 U mg⁻¹ and 2 ± 0.2 U mg⁻¹ (per mg commercial lipase preparation), respectively.