The C2-DIIS convergence acceleration algorithm

We present a theoretical and numerical comparison between two DIIS algorithms to which we refer herein as C ¹-DIIS and C ²-DIIS . The C ²-DIIS algorithm is shown to be equivalent to the traditional C ¹-DIIS algorithm near convergence and more stable numerically as regards the accumulation of round-off error when the C ¹-DIIS equations become (nearly) singular. The C ²-DIIS algorithm also offers alternative solutions to the DIIS equations when anharmonicities or numerical difficulties are problematic. These properties of the C ²-DIIS algorithm allow the use of much larger DIIS spaces, obviating the need for truncation of the DIIS space, which, when done, usually results in a loss of information contained in the iterated subspace. The C ²-DIIS method can be considered to be a variant of the singular value decomposition method. © 1993 John Wiley & Sons, Inc.     

Ab initio studies of structural features not easily amenable to experiment: The molecular structures of two low-energy forms of unionized serine

The structures of two unionized conformations of serine were refined without geometrical constraints using standard single determinant ab initio procedures on the 4-21G level. The results represent the best now available estimate for the unobserved equilibrium geometry of this system.     

The adiabatic correction to molecular potential surfaces in the SCF approximation

Formulas for the adiabatic correction to the potential energy in the SCF approximation are derived in a density matrix form.     

Determination of intraoperative plasma catecholamine concentrations using liquid chromatography with electrochemical detection

Liquid chromatography with electrochemical detection was used for the determination of norepinephrine and epinephrine in human plasma samples obtained prior to, after, and six times during the course of spinal fusion surgery for the correction of scoliosis. The catecholamines were extracted from plasma by alumina adsorption and chromatographed isocratically using a reversed-phase, ion-pairing system. Data obtained are compared to those obtained intraoperatively by other authors using a radioenzymatic method, and the mechanism of sympathetic activation during surgery is discussed. Preliminary data using 3-micron particle size columns and dual-parallel electrochemical detection are presented.     

Alkylation of H-phosphinate esters under basic conditions

An efficient and general procedure was developed for the direct alkylation of H-phosphinate esters with LHMDS at low temperature. The simplicity of the reaction allows the use of various H-phosphinate esters and takes place with a wide range of electrophiles. The approach can be employed to access some GABA analogues or precursors to GABA analogues. The isolated yields are moderate to good. This is the first report of an alkylation with a secondary iodide or a primary chloride.     

Lights, Camera, Action! systematic variation in 2-D difference gel electrophoresis images

2-D Difference gel electrophoresis (DIGE) circumvents many of the problems associated with gel comparison via the traditional 2-DE approach. DIGE's accuracy and precision, however, is compromised by the existence of other significant sources of systematic variation, including that caused by the apparatus used for imaging proteins (location of the camera and lighting units, background material, imperfections within that material, etc.). Through a series of experiments, we estimate some of these factors, and account for their effect on the DIGE experimental data, thus providing improved estimates of the true relative protein intensities. The model presented here includes 2-DE images as a special case.     

Structural and magnetic properties of Mn-doped anatase TiO<Subscript>2</Subscript> films synthesized by atomic layer deposition

Mn-doped anatase TiO₂ (Mn: 1.2, 2.4 at%) thin films were grown on Si(100) via atomic layer deposition (ALD). The synthesis utilized Ti(OCH(CH₃)₂)₄ and H₂O as ALD precursors and Mn(DPM)₃ as a dopant source. X-ray photoelectron spectroscopy measurements indicate that Mn is successfully doped in the TiO₂ matrix and reveal information about film composition and elemental chemical states. Microstructure, crystallinity, and density were investigated with scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. All ALD-synthesized films exhibited room-temperature ferromagnetism; the microstructure, density, and magnetic field-dependent magnetization of the TiO₂ varied with the concentration of Mn. ALD permits precise composition and thickness control, and much higher process throughput compared to alternative techniques.