Intramolecular basis set superposition error effects on the planarity of benzene and other aromatic molecules: A solution to the problem

Recently, the surprising result that ab initio calculations on benzene and other planar arenes at correlated MP2, MP3, configuration interaction with singles and doubles (CISD), and coupled cluster with singles and doubles levels of theory using standard Pople’s basis sets yield nonplanar minima has been reported. The planar optimized structures turn out to be transition states presenting one or more large imaginary frequencies, whereas single-determinant-based methods lead to the expected planar minima and no imaginary frequencies. It has been suggested that such anomalous behavior can be originated by two-electron basis set incompleteness error. In this work, we show that the reported pitfalls can be interpreted in terms of intramolecular basis set superposition error (BSSE) effects, mostly between the C–H moieties constituting the arenes. We have carried out counterpoise-corrected optimizations and frequency calculations at the Hartree–Fock, B3LYP, MP2, and CISD levels of theory with several basis sets for a number of arenes. In all cases, correcting for intramolecular BSSE fixes the anomalous behavior of the correlated methods, whereas no significant differences are observed in the single-determinant case. Consequently, all systems studied are planar at all levels of theory. The effect of different intramolecular fragment definitions and the particular case of charged species, namely, cyclopentadienyl and indenyl anions, respectively, are also discussed

Iterative image reconstruction techniques: cardiothoracic computed tomography applications.

Iterative image reconstruction algorithms provide significant improvements over traditional filtered back projection in computed tomography (CT). Clinically available through recent advances in modern CT technology, iterative reconstruction enhances image quality through cyclical image calculation, suppressing image noise and artifacts, particularly blooming artifacts. The advantages of iterative reconstruction are apparent in traditionally challenging cases-for example, in obese patients, those with significant artery calcification, or those with coronary artery stents. In addition, as clinical use of CT has grown, so have concerns over ionizing radiation associated with CT examinations. Through noise reduction, iterative reconstruction has been shown to permit radiation dose reduction while preserving diagnostic image quality. This approach is becoming increasingly attractive as the routine use of CT for pediatric and repeated follow-up evaluation grows ever more common. Cardiovascular CT in particular, with its focus on detailed structural and functional analyses, stands to benefit greatly from the promising iterative solutions that are readily available.

A-7 Statistical Report On FIP Applications And Cases Discontinued, July 2002

Monthly statistical report on FIP by Iowa Department of Human Services

A-7 Statistical Report On FIP Applications And Cases Discontinued, September 2003

Monthly statistical report on FIP by Iowa Department of Human Services

A-7 Statistical Report On FIP Applications And Cases Discontinued, November 2001

Monthly statistical report on FIP by Iowa Department of Human Services

A-7 Statistical Report On FIP Applications And Cases Discontinued, January 2002

Monthly statistical report on FIP by Iowa Department of Human Services

A-7 Statistical Report On FIP Applications And Cases Discontinued, June 2004

Monthly statistical report on FIP by the Iowa Department of Human Services

A-7 Statistical Report On FIP Applications And Cases Discontinued, July 2004

Statistical Report On FIP Applications And Cases Discontinued

A-7 Statistical Report On FIP Applications And Cases Discontinued, August 2004

Statistical Report On FIP Applications And Cases Discontinued

A-7, Statistical Report On FIP Applications And Cases Discontinued, September 2004

Statistical Report On FIP Applications And Cases Discontinued

A-7, Statistical Report On FIP Applications And Cases Discontinued, October 2004

Statistical Report On FIP Applications And Cases Discontinued

A-7 Statistical Report On FIP Applications And Cases Discontinued, November 2004

A-7 Statistical Report On FIP Applications And Cases Discontinued

New Radicals and new applications of Dynamic Nuclear Polarization of biological systems

Dynamic Nuclear Polarization (DNP) is an emerging technique that could revolutionize the NMR study of small molecules at very low concentrations by the increase in sensitivity that results from transfer of polarization between electronic and nuclear spins. Although the underlying physics has been known for a long time, in the last few years there has been a lot of excitement on the chemistry and biology NMR community caused by the demonstration that the highly polarized nuclei that are prepared in solid state at very low temperatures (1-2 K) could be rapidly transferred to liquid samples at room temperature and studied in solution by conventional NMR techniques. In favorable cases several order of magnitude increases in sensitivity have been achieved. The technique is now mature enough that a commercial instrument is available. The efficiency of DNP depends on two crucial aspects: i) the efficiency of the nuclear polarization process and ii) the efficiency of the transfer from the initial solid state to the fluid state in which NMR is measured. The preferred areas of application (iii) will be dictated by situations in which the low concentration of the sample or its intrinsic low receptivity are the limiting factors .

A-7 Statistical Report On FIP Applications And Cases Discontinued, November 2004 (Revised)

Statistical Report On FIP Applications And Cases Discontinued

A-7 Statistical Report On FIP Applications And Cases Discontinued, December 2004

Statistical Report On FIP Applications And Cases Discontinued