An abundance of nodulation factors

In this issue of Chemistry & Biology, Morón et al. [1] report that Rhizobium tropici CIAT899 produces different Nod factors in response to flavonoid induction under differing environmental conditions. This unanticipated environmental dependence has implications for altering or potentially improving the host-bacteria interaction in bean nodulation.     

Microdrops on atomic force microscope cantilevers: evaporation of water and spring constant calibration

The evaporation of water drops with radii approximately 20 microm was investigated experimentally by depositing them onto atomic force microscope (AFM) cantilevers and measuring the deflection versus time. Because of the surface tension of the liquid, the Laplace pressure inside the drop, and the change of interfacial stress at the solid-liquid interface, the cantilever is deflected by typically a few hundred nanometers. The experimental results are in accordance with an analytic theory developed. The evaporation process could be monitored with high accuracy even at the last stage of evaporation because (1) cantilever deflections can be measured with nanometer resolution and (2) the time resolution, given by the inverse of the resonance frequency of the cantilever of approximately 0.3 ms, is much faster than the typical evaporation time of 1 s. Experimental results indicate that evaporation of the last thin layer of water is significantly slower than the rest of the drop, which can be due to surface forces. This drop-on-cantilever system can also be used to analyze the drop impact dynamics on a surface and to determine the spring constant of cantilevers.     

On the [2,3] sigmatropic rearrangement of allylic nitro compounds

Allylic nitro compounds undergo relatively clean [2,3] sigmatropic rearrangement upon heating in refluxing 1,2-dichlorobenzene in the presence of DABCO to give the corresponding allylic alcohols via the intermediate allylic nitrite. [reaction: see text]     

Analysis of Ti-N films by calibration of Ti X-ray spectra

Summary An energy-dispersive X-ray analysis of Ti_1–xN_x films was performed by using an Si(Li) detector. The Ti_1–xN_x films were sputtered on polished steel substrates in a mixed Ar+N₂ atmosphere by a reactive magnetron sputtering technique. Because the nitrogen X-ray line is absorbed by the Be window, an analysis method was developed based solely on the calibration of the characteristic Ti-K-intensities using a high-purity Ti standard. The film compositions were computed by means of a ZAF procedure. The samples closest to stoichiometric composition show maximum hardness.     

Infinitesimal obstructions to weakly mixing

Let ^t be the flow (parametrized with respect to arc length) of a smooth unit vector field v on a closed Riemannian manifold M ⁿ , whose orbits are geodesics. Then the (n-1)-plane field normal to v, v, is invariant under d ^t and, for each x M, we define a smooth real function _x (t) : (1 + _i (t)), where the _i(t) are the eigenvalues of AA ^T, A being the matrix (with respect to orthonormal bases) of the non-singular linear map d^2t , restricted to v at the point _x ^-t M ⁿ.Among other things, we prove the Theorem (Theorem II, below). Assume v is also volume preserving and that _x ^' (t) 0 for all x M and real t; then, if _x ^t : M M is weakly missng for some t, it is necessary that vx 0 at all x M.     

Tetraaryl-methane analogues in group 14—V. Distortion of tetrahedral geometryin terms of through-space π–π and π–σ interactions andNMR sagging in terms of π–σcharge transfer

44 members of thecompound series Ph_4−nMR_n (M=Si, Ge, Sn, Pb; R=o-, m-, p-Tol; n=0–4) were synthesized (15 newcompounds). The crystal structures of Ph₃Sn (o-Tol) and PhSn (o-Tol)₃ were determined and compared to 16 known structures. Subject to the distanced (M–C), an interplay between through-space π–π repulsion and π–σ attraction leads to either elongated or compressed tetrahedral geometry. ²⁹ Si-, ¹¹⁹ Sn- and ²⁰⁷ Pb-NMR chemical shifts were determined in solution and in the solid state. ⁷³ Ge chemical shifts were measured only in solution. Anupfield or downfield sagging of the chemical shifts along each series is rationalized in terms of a π–σcharge transfer which is constrained by torsion of the aromatic groups.     

Horizontal bridges in polar dielectric liquids

When a high-voltage direct-current is applied to two beakers filled with polar liquid dielectrica like water or methanol, a horizontal bridge forms between the two beakers. By repeating a version of Pellat’s experiment, it is shown that a horizontal bridge is stable by the action of electrohydrodynamic pressure. Thus, the static and dynamic properties of the phenomenon called a ‘floating water bridge’ can be explained by the gradient of Maxwell pressure, replenishing the liquid within the bridge against any drainage mechanism. It is also shown that a number of liquids can form stable and long horizontal bridges. The stability of such a connection, and the asymmetry in mass flow through such bridges caused by the formation of ion clouds in the vicinity of the electrodes, is also discussed by two further experiments.     

Plasma generation in silicon-based inductive grid arrays

Selective illumination of a silicon wafer can be used for the construction of non-permanent inductive grids. A numerical model is used for the calculation of plasma density distribution in silicon as a function of time. Some indicative results on the microwave properties of the device are presented.     

Novel Dithiolene Complexes and Tetrathiafulvalenes

Abstract

Novel dithiolene metal complexes, some of which absorb in the near infrared, and tetrathiafulvalenes, in particular tetraiodotetrathia- fulvalene, have been prepared, and their magnetic properties studied.     

Selected parameters leading to an optimized DSSC performance

Dye Sensitized Solar Cells (DSSC), the third generation of photovoltaic devices, can be considered as most promising among renewable energy sources. Although DSSCs are devices very easy to fabricate, there is a large number of design parameters upon which their performance depends. In this review paper a lay out is given of the various parameters at which research groups focus aiming towards optimum performance of the DSSCs.