Ultraviolet-B-induced cyclobutane-pyrimidine dimer formation and repair in Arctic marine macrophytes

The significance of ultraviolet-B radiation (UVBR: 280-315 nm)-induced DNA damage as a stress factor for Arctic marine macrophytes was examined in the Kongsfjord (Spitsbergen, 78 degrees 55.5'N, 11 degrees 56.0'E) in summer. UVBR penetration in the water column was monitored as accumulation of cyclobutane-pyrimidine dimers (CPD) in bare DNA. This showed that UVBR transparency of the fjord was variable, with 1% depths ranging between 4 and 8 m. In addition, induction and repair kinetics of CPD were studied in several subtidal macrophytes obtained from the Kongsfjord (5-15 m). Surface exposure experiments demonstrated CPD accumulation in Palmaria palmata, Devaleraea ramentacea, Phycodrys rubens, Coccotylus truncatus and Odonthalia dentata. In artificial light, field collected material of P. palmata, D. ramentacea, P. rubens and Laminaria saccharina showed efficient CPD repair, with only 10% of the artificially induced CPD remaining after 5 h. No significant differences in repair rate were observed among these species. CPD repair was slower or absent in O. dentata, C. truncatus and Monostroma arcticum, indicating that fast repair mechanisms such as photolyase were not continuously expressed in these species. CPD repair rates were not directly related to the vertical distribution of algae in the water column and to the reported UV sensitivity of the examined species. Dosimeter incubations showed that maximal exposure to DNA damaging wavelengths was low for all examined species. Furthermore, most species collected below the 1% depth for DNA damage displayed efficient CPD repair, suggesting that UVBR-induced CPD currently impose a minor threat for mature stages of these species growing in the Kongsfjord, Spitsbergen.     

A perturbed pK(a) at the binding site of the nicotinic acetylcholine receptor: implications for nicotine binding

A series of tethered quaternary ammonium derivatives of Tyr have been incorporated into the binding site of the nicotinic acetylcholine receptor (nAChR) using the in vivo nonsense suppression method, producing constitutively active (self-gating) receptors. We have incorporated primary, secondary, and tertiary amine tethered agonists to give receptors whose constitutive activity can be modulated by pH. Lowering the pH protonates the tethered amine, giving it a positive charge and allowing it to reversibly activate the receptor. Tertiary and secondary tethered amines, TyrO3T and TyrO3S, have been successfully incorporated at alpha149 in the nAChR. Constitutive currents at pH 5.5 are 6 times those at pH 9.0. The pKa of TyrO3T in the binding site appears to be 6 or lower, differing substantially from its pKa in solution ( approximately 9.3). This local pKa perturbation has substantial implications for pharmacological research on the nAChR: of the tertiary agonists considered, noracetylcholine experiences this pKa perturbation, while nicotine does not.     

Carbonates,thiocarbonates, and the corresponding monoalkyl derivatives: III. The 13C chemical shift tensors in potassium carbonate,bicarbonate and related monomethyl derivatives

The principal values of the 13C chemical shift tensors in potassium carbonate (K2CO3), trithiocarbonate (K2CS3), bicarbonate (KHCO3), methylcarbonate (KO2COCH3), S-methyl-monothiocarbonate (KO2CSCH3), O-methyl-monothiocarbonate (KOSCOCH3), S-methyl-dithiocarbonate (KOSCSCH3), and O-methyl-dithiocarbonate (KS2COCH3), were measured in solid-state nuclear magnetic resonance experiments. Chemical shift tensor calculations on the corresponding isolated anions were used to assign the chemical shift tensor orientations in the molecular frames of all anions. The correlation between experimental and calculated principal values improves significantly when the calculations are performed on isolated anions with proton-optimized X-ray geometries rather than on isolated anions with fully optimized geometries. Further considerable improvement in the correlation is achieved by utilizing the embedded ion method, which was recently developed to include electrostatic crystal potentials in chemical shift tensor calculations on ionic compounds. Similarities and differences in the chemical shift tensor orientations and principal values of the trigonal sp2 carbon atoms in the carbonate and thiocarbonate anions are compared with those known for condensed polyaromatic hydrocarbons.     

Time-dependent entropies associated with single mode radiation in a cavity

The time-dependent information theory entropy and generalized Gibbs entropy are evaluated for a continuous time Markov process (single mode radiation in a cavity).     

Measurement of traffic noise shielding provided by buildings

This paper presents a comparison between some current prediction methods for traffic noise shielding provided by buildings and the actual measured attenuations in typical residential areas. Generally, it was found that the method developed by the Department of Environment in the UK gives a reasonably accurate prediction of attenuation by shielding in fairly simple situations. In more complex situations, and particularly where a receiving position is close to a significant shielding structure, such as building, the attenuation obtained is underpredicted by the DOE method, thus the design facade levels for the rear of a building are overpredicted; however, in some other situations, the DOE method overpredicts the attenuation obtained. The attenuations measured for individual noise events under nominally identical conditions are shown to have large variations in attenuation.     

beta-Sheet mediated self-assembly of dipeptides of omega-amino acids and remarkable fibrillation in the solid state

Single crystal X-ray diffraction studies show that the extended structure of dipeptide Boc-beta-Ala-m-ABA-OMe (m-ABA: meta-aminobenzoic acid) self-assembles in the solid state by intermolecular hydrogen bonding to create an infinite parallel beta-sheet structure. In dipeptide Boc-gamma-Abu-m-ABA-OMe (gamma-Abu: gamma-aminobutyric acid), two such parallel beta-sheets are further cross-linked by intermolecular hydrogen bonding through m-aminobenzoic acid moieties. SEM (scanning electron microscopy) studies reveal that both the peptides and form amyloid-like fibrils in the solid state. The fibrils are also found to be stained readily by Congo red, a characteristic feature of the amyloid fiber whose accumulation causes several fatal diseases such as Alzheimer's, prion-protein etc.     

Predicting thermal displacements in modular tool systems

In the last decade, there has been an increasing interest in compensating thermally induced errors to improve the manufacturing accuracy of modular tool systems. These modular tool systems are interfaces between spindle and workpiece and consist of several complicatedly formed parts. Their thermal behavior is dominated by nonlinearities, delay and hysteresis effects even in tools with simpler geometry and it is difficult to describe it theoretically. Due to the dominant nonlinear nature of this behavior the so far used linear regression between the temperatures and the displacements is insufficient. Therefore, in this study we test the hypothesis whether we can reliably predict such thermal displacements via nonlinear temperature-displacement regression functions. These functions are estimated first from learning measurements using the alternating conditional expectation (ACE) algorithm and then tested on independent data sets. First, we analyze data that were generated by a finite element spindle model. We find that our approach is a powerful tool to describe the relation between temperatures and displacements for simulated data. Next, we analyze the temperature-displacement relationship in a silent real experimental setup, where the tool system is thermally forced. Again, the ACE algorithm is powerful to estimate the deformation with high precision. The corresponding errors obtained by using the nonlinear regression approach are 10-fold lower in comparison to multiple linear regression analysis. Finally, we investigate the thermal behavior of a modular tool system in a working milling machine and again get promising results. The thermally induced errors can be estimated with 1-2 microm accuracy using this nonlinear regression analysis. Therefore, this approach seems to be very useful for the development of new modular tool systems.     

Microstructure of Nickel Aluminides Formed in Situ in Aluminium Matrix Composites

Nickel aluminides formed in situ in aluminium matrix composites due to the interaction between nickel powder and the matrix were examined. The composite materials were obtained from mixtures of nickel powder and aluminium powder by hot pressing in vacuum in the temperature range of 500–640°C. Depending on hot pressing parameters, the morphology of nickel aluminide particles was layered or homogenous, and their size for the same precursor powder was growing as the pressing temperature increased. XRD, SEM, TEM and EDS characterization methods were used for the microstructure investigation.     

Dialgebra cohomology as a G-algebra

It is well known that the Hochschild cohomology of an associative algebra admits a G-algebra structure. In this paper we show that the dialgebra cohomology of an associative dialgebra has a similar structure, which is induced from a homotopy G-algebra structure on the dialgebra cochain complex .