Single-detector micro-electro-mechanical scanning grating spectrometer

A compact, robust grating spectrometer based on an optimised micro-electro-mechanical grating mirror component has been developed, built, and characterised. The application of an oscillating reflection grating micro-mirror component as scanning dispersive element in a modified Czerny-Turner monochromator layout enables the design of compact grating spectrometers capable of acquiring full spectra using a single detector element. Designed for a wavelength range between 1200 and 1900 nm, the spectrometer features a spectral resolution of 10 nm with wavelength stability better than +/-0.5 nm. One-hundred scan spectra can be acquired in less than one second, or spectral changes can be monitored at time a resolution of less than 10 ms. In combination with a fibre-optic interface and a typical weight of less than 1 kg, this makes this novel type of fully portable micro-electro-mechanical near-IR scanning spectrometer an interesting alternative to existing spectrometers and opens a range of new applications, in particular the detection of major and minor components in the near-IR.

[Comments on the standards for acceptance and consistency testing of systems for digital radiography]

Due to German regulations, acceptance and consistency tests have to be obtained by 12.31.2005 for all equipment used for computed radiography according to special standards published in DIN 6868. This article familiarizes all users with the most important aspects of these standards. In addition, explanatory and background information for establishing these regulations are provided.

Organa– a program package for structure determination from powder diffraction data by direct-space methods

A new software package has been developed, namedOrgana, forab initiosolution of crystal structures from powder diffraction data by direct-space methods. The package contains energy-guiding Monte Carlo and grid-search algorithms and is based on a combined global minimization of theRfactor and a potential energy function of the system with the option of local minimization of the cost function for each generated trial structure. Basically, the potential energy function consists of van der Waals interactions, but harmonic potentials can be added to impose soft distance restraints. The program was successfully applied to the structure determination of a series of melamine phosphate compounds. The program is freely available (for all Windows platforms) from the correspondence author upon request.

Molecular simulations of smectites intercalated with a zirconium complex ion

Molecular mechanics simulations using the Cerius2 modeling environment have been applied to study the structures of dioctahedral smectites intercalated with the zirconium cation [Zr4(OH)12(H2O)12]4+. The substitutions in the silicate layers influence the sublimation energy in these types of intercalated layer structures. Charge distribution in the smectite layer was analyzed in relation to the interlayer structure. Tetrahedral substitutions in the smectite layer create preferential interlayer positions of the [Zr4(OH)12(H2O)12]4+ ion. A regular distribution of the tetrahedral substitutions in the smectite layer results in a better intercalant ordering in the interlayer space. Such a more homogeneous intercalant distribution results in a better interlayer pore size control.

Intermolecular -CH(3)...O(2)N-- contacts in two polymorphic modifications of (1E)-N'-[(E)-2-cyano-1-(dimethylamino)-2-nitrovinyl]-N,N-dimethylethanimidamide

The title compound was synthesized and isolated in two crystal modifications. The structure of the orthorhombic modification was determined by the X-ray powder diffraction method and the structure of the monoclinic modification was determined using the X-ray single-crystal diffraction technique. The molecules in both polymorphs are E,E isomers. Intermolecular H(3)C....NO(2) contacts and their role in the formation of the polymorphic modifications are analyzed.

A Monte Carlo approach to crystal structure determination from powder diffraction data

A new direct-space method forab initiosolution of crystal structures from powder diffraction data is presented. The approach consists of a combined global minimization ofRwpand the potential energy of the system. This method was tested on two organic compounds with known structure and also applied successfully in the structure determination of the previously unknown structure of melamine pyrophosphate.

Clustered DNA damages induced by high and low LET radiation, including heavy ions

Clustered DNA damages--here defined as two or more lesions (strand breaks, oxidized purines, oxidized pyrimidines or abasic sites) within a few helical turns--have been postulated as difficult to repair accurately, and thus highly significant biological lesions. Further, attempted repair of clusters may produce double strand breaks (DSBs). However, until recently, there was no way to measure ionizing radiation-induced clustered damages, except DSB. We recently described an approach for measuring classes of clustered damages (oxidized purine clusters, oxidized pyrimidine clusters, abasic clusters, along with DSB). We showed that ionizing radiation (gamma rays and Fe ions, 1 GeV/amu) does induce such clusters in genomic DNA in solution and in human cells. These studies also showed that each damage cluster results from one radiation hit (and its track), thus indicating that they can be induced by very low doses of radiation, i.e. two independent hits are not required for cluster induction. Further, among all complex damages, double strand breaks comprise--at most-- ~20%, with the other clustered damages being at least 80%.

Powder diffraction study of the hydrogen bonds in nitroxoline and its hydrochloride

The crystal structures of 8-hydroxy-5-nitroquinoline, C9H6N2O3, (I), and 8-hydroxy-5-nitroquinolinium chloride, C9H7N2O3+*Cl-, (II), have been determined from X-ray powder data. In (I), the molecules are linked via moderately strong hydrogen bonds to form dimers. Such a packing motif is likely to be responsible for the low solubility of (I) in water. In (II), the inversion-related cations form stacks, and anions fill the interstack channels.