1,309 research outputs found
Infrared Spectra and Ab Initio Calculations for the F-−(CH4)n (n = 1−8) Anion Clusters
Infrared spectra of mass-selected F-−(CH4)n (n = 1−8) clusters are recorded in the CH stretching region (2500−3100 cm-1). Spectra for the n = 1−3 clusters are interpreted with the aid of ab initio calculations at the MP2/6-311++G(2df 2p) level, which suggest that the CH4ligands bind to F- by equivalent, linear hydrogen bonds. Anharmonic frequencies for CH4 and F-−CH4 are determined using the vibrational self-consistent field method with second-order perturbation theory correction. The n = 1 complex is predicted to have a C3v structure with a single CH group hydrogen bonded to F-. Its spectrum exhibits a parallel band associated with a stretching vibration of the hydrogen-bonded CH group that is red-shifted by 380 cm-1 from the ν1 band of free CH4 and a perpendicular band associated with the asymmetric stretching motion of the nonbonded CH groups, slightly red-shifted from the ν3 band of free CH4. As nincreases, additional vibrational bands appear as a result of Fermi resonances between the hydrogen-bonded CH stretching vibrational mode and the 2ν4 overtone and ν2 + ν4combination levels of the methane solvent molecules. For clusters with n ≤ 8, it appears that the CH4 molecules are accommodated in the first solvation shell, each being attached to the F- anion by equivalent hydrogen bonds
The Panchromatic Hubble Andromeda Treasury. Progression of Large-Scale Star Formation across Space and Time in M31
We investigate the clustering of early-type stars younger than 300 Myr on
galactic scales in M31. Based on the stellar photometric catalogs of the
Panchromatic Hubble Andromeda Treasury program that also provides stellar
parameters derived from the individual energy distributions, our analysis is
focused on the young stars in three star-forming regions, located at
galactocentric distances of about 5, 10, and 15 kpc, corresponding to the inner
spiral arms, the ring structure, and the outer arm, respectively. We apply the
two-point correlation function to our selected sample to investigate the
clustering behavior of these stars across different time- and length-scales. We
find that young stellar structure survives across the whole extent of M31
longer than 300 Myr. Stellar distribution in all regions appears to be
self-similar, with younger stars being systematically more strongly clustered
than the older, which are more dispersed. The observed clustering is
interpreted as being induced by turbulence, the driving source for which is
probably gravitational instabilities driven by the spiral arms, which are
stronger closer to the galactic centre.Comment: 10 pages, 5 figures. To appear in "LESSONS FROM THE LOCAL GROUP - A
Conference in Honour of David Block and Bruce Elmegreen" eds. Freeman, K.C.,
Elmegreen, B.G., Block, D.L. & Woolway, M. (Springer: New York
Spatial normalization of reverse phase protein array data.
Reverse phase protein arrays (RPPA) are an efficient, high-throughput, cost-effective method for the quantification of specific proteins in complex biological samples. The quality of RPPA data may be affected by various sources of error. One of these, spatial variation, is caused by uneven exposure of different parts of an RPPA slide to the reagents used in protein detection. We present a method for the determination and correction of systematic spatial variation in RPPA slides using positive control spots printed on each slide. The method uses a simple bi-linear interpolation technique to obtain a surface representing the spatial variation occurring across the dimensions of a slide. This surface is used to calculate correction factors that can normalize the relative protein concentrations of the samples on each slide. The adoption of the method results in increased agreement between technical and biological replicates of various tumor and cell-line derived samples. Further, in data from a study of the melanoma cell-line SKMEL-133, several slides that had previously been rejected because they had a coefficient of variation (CV) greater than 15%, are rescued by reduction of CV below this threshold in each case. The method is implemented in the R statistical programing language. It is compatible with MicroVigene and SuperCurve, packages commonly used in RPPA data analysis. The method is made available, along with suggestions for implementation, at http://bitbucket.org/rppa_preprocess/rppa_preprocess/src
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