Direct methods acceleration

In principle, a direct electron accelerator consists of a high-voltage generator connected to an evacuated acceleration system. The different direct accelerators currently used employ similar methods for electron emission, acceleration, and dispersion the differences are in the design of their voltage generators. 

An interesting variation on the deflection method has been reported [668, 893] in which the component of velocity normal to the direction of acceleration is measured by mechanically moving an aperture across the beam. No electrostatic deflection is employed. The aperture is situated some distance from the source in front of the mass spectrometer and, in effect, determines how far off axis ions have moved since they left the source. 

For the preparation of 1,2-diketones the coupling of acyl cyanides is a direct method. Enones undergo reductive dimerization at the P-position which is followed by an aldol reaction in sterically favorable cases.Benzylideneimines give mainly syn-1,2-diamines in the reductive coupling which is also accelerated by Yb(OTf)3. 

An improvement on the simple steepest descent method was made by Schleyer (Engler et al., 1973), and utilized the pattern search procedure. In this case the method proceeds as before, but information regarding the direction of motion of the atoms is saved from one iteration to the next, and the correction terms for succeeding motions are summed, and then applied. The advantage of this method is that if a particular atom is moving down a long hill with small slope, while the steepest descent method requires many iterations to move it, the pattern search method accelerates the motion, because the motion is repeatedly in the same direction, and the size of the correction term increases. 

Direct determination of solids may be performed by, e.g.. X-ray fluorescence spectrometry, or by arc or spailr emission spectrometry in case of powders. For special applications many surface techniques are available such as proton-induced X-ray emission (PIXE) and laser microprobe emission spectrometry (LMA). In the case of determination of trace elements on clinical material, however, most of these direct methods have detection limits that are too high to be useful. Moreover, as some of these methods are cormected to an accelerator or electron microscope, usage is somewhat limited for routine determination. 

In this method, accelerated ions such as Ar+ are directed toward the surface of a target to eject atoms and small clusters from its surface. The ions are carried to the substrate under a relatively high pressure ( 1 mTorr) of an inert gas, causing aggregation of the species. Nanoparticles of metals and alloys as well as... 

In the equivalent static method, first the base shear is calculated, which is then distributed over the height of the building as specified by the pertinent seismic code. In the response spectmm analysis, for a given direction of acceleration, the... 

Direct addition of ammonia to olefmic bonds would be an attractive method for amine synthesis, if it could be carried out smoothly. Like water, ammonia reacts with butadiene only under particular reaction conditions. Almost no reaction takes place with pure ammonia in organic solvents. The presence of water accelerates the reaction considerably. The reaction of aqueous ammonia (28%) with butadiene in MeCN in the presence orPd(OAc)i and PhjP at 80 C for 10 h gives tri-2,7-octadienylamine (47) as the main product, accompanied by a small amount of di-2,7-octadienylamine (46)[46,47], Isomeric branched... 

When three-point interpolation fails to yield a convergent calculation, you can request a second accelerator for any SCFcalculation via the Semi-empirical Options dialog box and the Ab Initio Options dialog box. This alternative method. Direct Inversion in the Iterative Subspace (DIIS), was developed by Peter Pulay [P. Pulay, Chem. Phys. Lett., 73, 393 (1980) J. Comp. Chem., 3, 556(1982)]. DIIS relies on the fact that the eigenvectors of the density and Fock matrices are identical at self-consistency. At SCF convergence, the following condition exists... 

In some cases, particularly with iaactive metals, electrolytic cells are the primary method of manufacture of the fluoroborate solution. The manufacture of Sn, Pb, Cu, and Ni fluoroborates by electrolytic dissolution (87,88) is patented. A typical cell for continous production consists of a polyethylene-lined tank with tin anodes at the bottom and a mercury pool (ia a porous basket) cathode near the top (88). Pluoroboric acid is added to the cell and electrolysis is begun. As tin fluoroborate is generated, differences ia specific gravity cause the product to layer at the bottom of the cell. When the desired concentration is reached ia this layer, the heavy solution is drawn from the bottom and fresh HBP is added to the top of the cell continuously. The direct reaction of tin with HBP is slow but can be accelerated by passiag air or oxygen through the solution (89). The stannic fluoroborate is reduced by reaction with mossy tin under an iaert atmosphere. In earlier procedures, HBP reacted with hydrated stannous oxide. 

---