Attack angle

A) H.A, Wetmore, Octol (HMX/TNT) A literature Review , PicArsnLiterature Search No 10 (1960) (Conf) B) J.K. Fleming, Underwater Shaped-Charge Tests. Phase II - Attack Angle. Study , DTMB C-1462 (1963) (Conf)... 

The radiographs allowed one to find out how the velocity and the cylinder wall attack angle vary with the distance to the axis and consequently the diameter of the charge. 

Detailed studies have shown some further dependence of the wear rate on the attack angle, temperature of erosion, particle size, particle concentration, and particle hardness ... 

With complexes, the only dynamical calculations to date have been classical trajectories in which it was assumed that there is no significant C-Br chemical interaction following photoexcitation (Schatz and Fitzcharles 1988). Consequently, the role of the complex has been limited to H + C02 interactions sampled over the probability density for the intermolecular degrees of freedom, as well as the squeezed atom effect. These calculations have yielded reaction probabilities versus attack angle and nascent V, R, T excitations which are in reasonable agreement with the experimental results. Much work is still needed and the challenges are daunting. 

Fig. 5a,b Schematic representation of a the tip-sample contact upon high loading b the according compliance curve. In the case of perfectly plastic response the unloading curve is identical to the vertical line intersecting with the abscissa at hmax. In general, some viscoelastic recovery occurs and the residual impression depth hy is smaller than hmax. The difference hc—hy represents the extent of viscoelastic recovery. Ap and Ae denote the dissipated and the recovered work, respectively. Ap=0 for perfect elastic behaviour, whereas Ae=0 for perfect plastic behaviour. The viscoelastic-plastic properties of the material may be described by the parameter Ap(Ap+Ae) l. The contact strain increases with the attack angle 6. Adapted from [138]... 

Distances and angles (Figure 1) are in angstrom and degrees, respectively. The average values, denoted as (...), are obtained by averaging over all snapshots in the cluster. R is the in-line attack distance (C17 02 to C1.1 P). 6 is the in-line attack angle (between C17 02, C1.1 P, and C1.1 05 ). N is the number of ions with at least one coordination to any one of the four coordination sites. CN is the total coordination number of all ions with at least one coordination to any one of the four coordination sites. NB is the number of ions which coordinate to at least two of the four coordination sites. 

The same U-trees rotated to an attack angle of a = 45° constituted the 45°-canopy . The angled crowns naturally resulted in a modification of the internal flow so that its direction was very different from the direction of the external flow along the wind tunnel. 

Subsequently, the difference in the attack angle on a double bond between a nucleophile and an electrophile was postulated by Houk et al. [33] to be a major factor responsible for the different sense of 1,2-asymmetric induction. Since transition state B is less hindered than A in the case of hydroboration of alkenes or borane reduction of ketones (Scheme 6.27, right), it was proposed that such reactions should have a stereochemistry opposite to that obtained in metal hydride reductions (Scheme 6.27, left). The experimental results, indeed, confirm the reversal of the product ratios [178]. 

In fact, in 1980, Menger et al. showed that the differences in the attack angle up to 10° have no effect on the rates of lactonization in a model system [185]. Furthermore, the O... C distancs and O... C-C angles, calculated by Houk et al. using the MM2 force field [186], did not show any correlation with experimental rate constants for lactonization of the 15 hydroxyacids studied by Koshland et al. [46], Milstein and Cohen [187], and Menger and Glass [185b]. 

The most important process (which accounts for most of the uses of radical cychzations in synthesis) is the selective 5-exo-cyclization of the 5-hexenyl radical to give the cyclopentyl methyl radical. This occurs even though the alternative - a 6-endo cyclization to give a more stable, cyclohexyl radical - is thermodynamically more favorable. Thus, the 5-ex o-cycHzation proceeds under kinetic control. The preference for 5-ex o-cyclization is explained by an early transition state with little product character. The transition state is a strain-free chair-like arrangement, which nicely accommodates the stereoelectronically required attack angle on the alkene. This model also nicely explains the stereochemical outcome of the cycHzation reaction. Assuming that substituents prefer to adopt pseudo-equatorial positions in the chair-Uke transition state, we see why ... 

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