True NCS

Tme NCS occurs much more frequently than global pseudo-symmetry. The only problem it causes is the somewhat longer time and effort it takes to refine the structure, simply due to the much larger number of independent atoms. On the other hand, in some cases—for example for a protein structure with a very low data-to-parameter 

Molecule 2 crystallizes in the monoclinic space group P2i /n (unit cell dimensions a = 8.265(2), b = 8.228(2), c = 9.178(2), p = 101.14(3)) with half a molecule in the asymmetric unit. The other half is generated by the inversion centre of the 

In Table 6.1, tbe four rows teU us tbe following N is tbe number of independent reflections that should be absent if the respective symmetry element is present. The second row describes how many of those N reflections are stronger than three times their own standard uncertainty. l in the third row is the average intensity of the N reflections and l/s in the last row describes the average I/a value of the reflections that should be absent in the presence of the respective symmetry element. The systematic absences clearly indicate the presence of a glide plane in the direction of n and the absence of an a or c glide plane. The situation for the twofold screw axis is less clear. Half of the 33 reflections 0 0 with k 2n that should be absent for a monoclinic 2i -axis are observed, however those observed are significantly weaker than the rest of the data. 

Most of the anisotropic model looks reasonable, and all hydrogen atoms can be found in the difference Eourier map. However, the disordered carbon, atom C(6), is non-positive definite (NPD). A quick temporary fix is to constrain the anisotropic displacement parameters of C(6) to be identical with those of S(2). This can be 

Sometimes SHH XS finds two groups of potential solutions, where one corresponds only to a pseudo-solution. If this pseudo-solution has the lower combined figure of merit of the two, the program will chose it over the correct solution. In such a case it is common practice to examine the SHELXS. 1st file, identify the odier possible solution and run the program a second time specifying die seminvariants in the TREF command. This book is about structure refinement, not die solution of die phase problem and for furdier details die reader is referred to the SHELX manual or the original publication (Sheldrick, 1990). 

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Note in this large patient the periphery of the abdomen is not included in the B detector FOV (yellow circle), d True NC image in same patient shows the lesion has high-density, measuring 72 HU. This case demonstrates how a virtual noncontrast image can be used if a true NCCT is unavailable... 

The important observation from the data in Table 3 is that NC samples subjected to acid bod followed by tetrahydrofuran (THF)-benzene treatment yielded essentially the same sulfate contents as samples subjected to THF-benzene treatment alone. From this the authors interpret that sulfate contents from THF-benzene treatments actually represent absolute values of the difficult-to-remove sulfate which may very well be true sulfate ester . It is also tentatively concluded that approximately 90% of the original sulfate content in unstabilized NC is readily removable sulfuric acid with the remainder the more difficult-to-remove sulfate ester. Dilute acid boil treatment of NC for 56 hours does not eliminate all of the free sulfuric acid and leaves the difficult-to-remove sulfate practically unchanged... 

To solve Equation 9.51, it is necessary to know the values of not only a ,-j and 9 but also x, d. The values of xitD for each component in the distillate in Equation 9.51 are the values at the minimum reflux and are unknown. Rigorous solution of the Underwood Equations, without assumptions of component distribution, thus requires Equation 9.50 to be solved for (NC — 1) values of 9 lying between the values of atj of the different components. Equation 9.51 is then written (NC -1) times to give a set of equations in which the unknowns are Rmin and (NC -2) values of xi D for the nonkey components. These equations can then be solved simultaneously. In this way, in addition to the calculation of Rmi , the Underwood Equations can also be used to estimate the distribution of nonkey components at minimum reflux conditions from a specification of the key component separation. This is analogous to the use of the Fenske Equation to determine the distribution at total reflux. Although there is often not too much difference between the estimates at total and minimum reflux, the true distribution is more likely to be between the two estimates. 

Figure 3.54 shows the form of two singly occupied spin-NBOs in the vinylamine triplet excited state the 7tCN 1 half-bond of the (3 spin set (Fig. 3.54(a)) and the terminal nc radical orbital of the a spin set (Fig. 3.54(b)). Neither of these orbitals has a true counterpart in the MOs or NBOs of the ground-state molecule. These results emphasize that hyperconjugative reorganization is a strong feature of the excited-state orbitals, and the oversimplified HOMO-LUMO (Koopmans-like)... 

In a steady state in an NC system X is maintained constant. Because the local form of detailed balance, Eq. (47), holds, the main results of Section III follow. In particular, the nonequilibrium equality in Eq. (16) and the FT in Eq. (27) are still true. However, there is an important difference. In steady states the reverse process is identical to the forward process, Pf([Pg.53]

The possible outcomes obtained when the 4 sequences of alternative tests and the Draize test are applied to the data for the 51 chemicals are summarized in Table 18.8, along with the outcome of applying just one in vitro test (the EPISKIN test) before the Draize test. For each sequence, Table 18.8 gives the number of chemicals that enter each step, the distribution of these chemicals in terms of their known corrosion potential (C or NC), the number of positive predictions (i.e., chemicals for which no further assessment is made), and the numbers of true and false positives. 

It may be noted that the sine-functions transform amongst themselves under Ry(0) and the same is true for the cosine-functions provided the a-iunction is included in their set.2) We further note that xy > and yz > seen from the Y-axis make up the ns and nc functions, respectively. 

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