Biosensors based on immobilized insects fragments

The application of insect-sensing organs as parts of advanced biosensor devices with an electronic reading of the signals produced by the biological component is briefly reviewed, and some future applications are discussed. Dedicated to Professor Dr. Yakov I. Tur'yan on the occasion of his 85th birthday.     

Exploration of high‐resolution ultrasonic spectroscopy as an analytical tool to study demixing and remixing in poly(N‐isopropyl acrylamide)/water solutions

The ultrasonic properties of poly(N‐isopropyl acrylamide) (PNIPAM)/water solutions, determined with high‐resolution ultrasonic spectroscopy (HR‐US), change during demixing and remixing. All HR‐US measurements are discussed with respect to modulated temperature differential scanning calorimetry results. The lower critical solution temperature type of phase behavior, in combination with the glass‐transition/composition curve of PNIPAM/water, determines the evolution of the ultrasonic signals. Three different temperature regions can be distinguished: a homogeneous region and a heterogeneous region, the latter subdivided into zones without and with interference of partial vitrification of the PNIPAM‐rich phase. During phase separation, the ultrasonic velocity decreases because of a change in the hydration structure around the polymer chains, whereas the ultrasonic attenuation increases as aggregation sets in. Isothermal measurements clearly show time dependence for both the velocity and the attenuation. The observed timescales are different and can be related to a changing polymer/water interphase and aggregate formation, respectively. Partial vitrification of the PNIPAM‐rich phase slows the demixing kinetics and especially the remixing kinetics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1283–1295, 2005     

Self-self-dual spaces of polynomials

A space of polynomials V of dimension 7 is called self-dual if the divided Wronskian of any 6-subspace is in V. A self-dual space V has a natural inner product. The divided Wronskian of any isotropic 3-subspace of V is a square of a polynomial. We call V self-self-dual if the square root of the divided Wronskian of any isotropic 3-subspace is again in V. We show that the self-self-dual spaces have a natural non-degenerate skew-symmetric 3-form defined in terms of Wronskians.We show that the self-self-dual spaces correspond to G₂-populations related to the Bethe Ansatz of the Gaudin model of type G₂ and prove that a G₂-population is isomorphic to the G₂ flag variety.     

Atomic resolution in dynamic force microscopy across steps on Si(1 1 1)7×7

In this note we report the first observation of salient features of the Si(1 1 1)7×7 reconstructed surface across monatomic steps by dynamic atomic force microscopy (AFM) in ultrahigh vacuum (UHV). Simultaneous measurements of the resonance frequency shift Δf of the Si-cantilever and of the mean tunneling current ī _i from the cleaned Si tip indicate a restricted range for stable imaging with true atomic resolution. The corresponding characteristics vs. distance reveal why feedback control via Δf is problematic, whereas it is as successful as in conventional STM via ī _i .     

Transient field measurements on56Fe- and80Se-ions using segmented Fe-layers

Measurements of transient magnetic fields (TF) were performed on swift heavy ions of⁵⁶Fe and⁸⁰Se, with Coulomb excitation of their first 2⁺ state as probe, traversing thin Fe layers with segmented and unsegmented structures. The 50 µm×50 µm squares of the segments were accomplished applying the techniques of photolithography and ion etching. The magnitude of the TF deduced clearly shows that by segmentation of the targets the ion beam induced attentuations can be eliminated. This finding has direct applications tog-factor measurements.     

Narrow Band Gap Compounds with β-Pyrochlore Structure in the A2O-V2O5-2TeO3 (A=Rb,Cs) System

Two new isostructural compounds with composition of Rb⁺V³⁺_0.125V⁵⁺_0.625Te⁶⁺_1.25O₆ and Cs⁺V³⁺_0.125V⁵⁺_0.625Te⁶⁺_1.25O₆ have been synthesized by solid-state reaction. The crystal structure has been determined by X-ray diffraction analysis using Rietveld refinement. Both compounds possess β-pyrochlore structure-type with cubic space group Fd-3 m (Z=8); the unit cell parameters: a=10.04120(27) Å for RbV_0.75Te_1.25O₆ Å and a=10.09119(23) Å for CsV_0.75Te_1.25O₆. The oxidation states of vanadium and tellurium have been confirmed by X-ray photoelectron spectroscopy. The compounds contain vanadium in mixed valence state (3+ and 5+). The compounds possess the unusual narrow band gap for oxide compounds – in the infrared (IR) range (∼0.6 eV). The schematic electronic structure of the compounds has been estimated using XPS, UPS and electronic conductivity data; however, the shifts of the top of the valence edge and the bottom of the conduction band in the water conditions have been calculated using theoretical approximation. The thermal behavior of obtained compounds has been studied by differential thermal analysis. RbV_0.75Te_1.25O₆ and CsV_0.75Te_1.25O₆ melts at low temperatures (∼500 °C) with decomposition and weight loss. The RbV_0.75Te_1.25O₆ powder decomposes to amorphous phase, whereas CsV_0.75Te_1.25O₆ transform into new β-pyrochlore compound with another composition.     

MAB,a generally applicable molecular force field for structure modelling in medicinal chemistry

Summary The mathematical formulation, parametrization scheme, and structural results of a new, generally applicable molecular force field are presented. The central features are a scheme for automatic parameter assignments, the consistent united-atom approximation, the absence of atom types other than elements, the replacement of electrostatic terms by geometrical hydrogen-bonding terms, the concomitant lack of a need for partial atomic charge assignment and the strict adherence to a finite-range design. As a consequence of omitting all hydrogen atoms, optimal hydrogen-bond patterns are computed dynamically by appropriate network analyses. For a test set of 1589 structures, selected from the Cambridge Structural Database solely on the grounds of a given element list and criteria for high structure refinement, the agreements are on average 2 pm for bonds, 2° for valence angles and 10 to 20 pm for the root-mean-square deviation of atom positions, depending somewhat on size and flexibility of the structures. More qualitative testing of large-scale structural properties of the force field on proteins and DNA oligomers revealed satisfactory performance.     

Ellipticity dependence of atomic and molecular high harmonic generation

High harmonic generation is compared in the dependence on the ellipticity of the fundamental laser radiation for an atomic and a molecular system. In particular argon and nitrogen are compared employing molecular beams and intense ( 3×10¹⁴ W/cm²) and ultrashort (80 fs) 800 nm laser pulses. It turns out that for all the harmonics under investigation (H5, H13 and H21) the harmonic yield decreases slower with the ellipticity for the molecule than for the atom. This indicates differences in atomic and molecular high harmonic generation. Received 24 April 2002 Published online 24 September 2002     

Generic shapes for the conformation analysis of macrocyclic structures

A new algorithm for the systematic generation of conformations of macrocyclic systems is presented. The procedure is based on the concept of generic shapes that are found in such structures. These shapes are characterized by a selection of harmonics which occur in an approximate Fourier representation of the atomic coordinates of the rings. Following a fixed protocol, a limited set of in-plane and out-of-plane circular harmonics is used to define an ensemble of generic ring shapes. These generic shapes are used as start structures for energy minimizations by a given force-field method. To account for the possibility of having several final conformations originating from the same generic shape, the corresponding initial structure is taken several times and subjected to a randomization step before minimization. The resulting conformations that fall within a preset low-energy band are collected and screened for duplicates and enantiomers. The efficiency of this procedure (ratio between the number of accepted conformations and the total number of energy minimizations) depends on the flexibility of the macrocyclic system. The efficiency is generally quite high for very flexible rings. According to the proposed protocol, the number of generic shapes used as start structures grows as the square of N(lnN), where N is the ring size. The algorithm lends itself to conformational analyses of medium-size and large rings as well as of loops spanned between fixed structural units.