Thermoreflectance spectroscopy of systems showing charge density wave transitions

The thermoreflectance spectra of 1T-TaS₂, -TaSe₂ and alloys of these compounds have been measured and show substantial changes at the different charge density wave transitions. The changes include the appearance of new structure and the modification of the shape and sign of the modulated spectra. These changes are due to the new gaps introduced into the band structure by the presence of a charge density wave.     

Evaluation of MINDO/3 calculated structures. III. Saturated acyclic compounds with chlorine,nitrogen, oxygen,or sulfur

Fifty-one structures have been calculated by the MINDO /3 method to evaluate the errors introduced by branching and by the presence of the heteroatom. The structures are evaluated by comparisons which reveal that the calculated ΔH_f values reflect a bias because of the presence of the heteroatom. With two carbons or more in a chain attached to a heteroatom group, a linear relationship exists which makes possible the calculation of reasonably accurate ΔH_f values for unbranched alcohols, primary or secondary amines, ethers, thioethers, thiols, and alkyl chlorides. Branching errors do not seem to be linearly related among the systems. Some errors in calculations of geometries are also discussed.     

DNA DAMAGE IN RAT 9L CELLS TREATED WITH 8-METHOXYPSORALEN AND NEAR-UV LIGHT ASSAYED BY VISCOELASTOMETRY AND S1 NUCLEASE

–The techniques of viscoelastometry and S1 nuclease digestion were applied to the analysis of DNA damage in rat 9L cells treated with the combination of 8-MOP (8-methoxysporalen) and near-UV light. Treatment of cells with near-UV light alone resulted in a decrease in the viscoelastic retardation time under both denaturing and nondenaturing conditons. Exposure of cells to 8-MOP alone yielded a maximum in the plot of retardation time vs dose under nondenaturing conditions, similar to that found with ionizing radition. This observation suggests that treatment with 8-MOP alone leads to DNA strand breaks. Viscoelastic analysis of cell lysates under denaturing conditions demonstrated that treatment of cells with 8-MOP and UV radiation led to substantial increases in both the viscoelastic retardation time and recoil, consistent with formation of DNA interstrand cross-links. Viscoelastic analysis of cell lysates under nondenaturing conditions showed that exposure to long wavelength UV light in the presence of 8-MOP produced a decrease in retardation time. This decrease reflects the combined effect of strand breaks and interstrand cross-links. Results from the S1 nuclease assay confirmed these observations and permitted quantitation of DNA damage arising from single-strand breaks and DNA interstrand crosslinks. The importance of including the effect of strand breaks in the quantitation of cross-link formation is discussed.     

Evaluation of MINDO/3 calculated structures. II. Branching errors in alkanes and cycloalkanes

MINDO/3 calculations have been carried out for a series of branched chain alkanes in order to assess effects of branching on calculated geometries and heats of formation (ΔH_f). With vicinal branching, MINDO/3 calculates the central C? C bond to be too long. Bond angles are also found to be distorted. Errors in calculated heats of formation are large when geminal branching is present and significant with vicinal branching. Branching error corrections for ΔH_f have been derived and applied to a separate series of branched acyclic and cyclic compounds. For the test sample, application of the branching error corrections gave calculated structures of acyclic branched hydrocarbons with heats of formation having an average absolute error of 1.3 kcal/mole rather than 17.3 kcal/mole before correction. Cyclic branched hydrocarbons are shown to be less well corrected. Calculations of heats of reaction have also been carried out for some isomerization and cyclization reactions using the MINDO/3 and MNDO methods. It is clear from the comparisons that MNDO calculations give less severe errors for highly branched compounds but the errors are still substantial. For prediction of heats of reaction, the error-corrected calculations are shown to be superior to the “raw” calculations obtained by MINDO/3 or MNDO.     

Distribution patterns of Mimbres ceramics using INAA and multivariate statistical methods

The distribution patterns of Classic Mimbres black-on-white bowls and jars were determined by instrumental neutron activation analysis to identify vessel movement between geographically defined regions and between villages within individual regions of southwestern New Mexico. The data set produced and utilized by the various multivariate statistical treatments included multielement neutron activation analysis results for 288 ceramic and clay samples from 15 sites in the Gila, Mimbres and Rio Grande valleys of southwest New Mexico. The results indicate that bowls were more frequently exchanged than jars and distribution frequencies between regions were lower than between villages. Two statistical approaches to the data were compared. In one, cluster analysis of the compositional data was used to form homogeneous groups and the distribution of those groups across sites and regions was examined. In the second, discriminant analysis was used to look for significant differences in composition between regions and sites. The significance of predetermining groups based on collection location as opposed to blind group formation from hierarchical cluster analysis was evaluated in terms of its potential to lead to different interpretations of the data.