TRIPOD approach

The benefits claimed for the TRIPOD approach are that it provides a consistent method for auditing a situation to identify deficiencies in the factors that are likely to give rise to errors. These deficiencies can then be corrected to reduce the likelihood of accidents occurring in the future. 

HFAM has 20 groups of factors instead of the 10 general failure types of the TRIPOD approach. The reason for this is that all of the 10 TRIPOD GFTs would be applied in all situations, even though the actual questions that make up the factors may vary. In the case of HFAM, it would be rare to apply all of the factors unless an entire plant was being evaluated. HFAM uses a screening process to first identify the major areas vulnerable to human error. The generic factors and appropriate job specific factors are then applied to these areas. For example, control room questions would not be applied to maintenance jobs. 

Usually, in AFM the position of the tip is fixed and the sample is raster-scanned. After manual course approach with fine-thread screws, motion of the sample is performed with a piezo translator made of piezo ceramics like e. g. lead zirconate tita-nate (PZT), which can be either a piezo tripod or a single tube scanner. Single tube scanners are more difficult to calibrate, but they can be built more rigid and are thus less sensitive towards vibrational perturbations. 

Even with the foot, the vibration problem in such STM designs has not been resolved sufficiently. In fact, the tripod scanner has a relatively low natural vibration frequency, and the approaching mechanism is relatively bulky. In actual application, a four to-six element metal-plate stack with viton separators is used for vibration isolation. In order to achieve atomic resolution, a spring stage, either suspension spring or compression spring, is neces-... 

Dual-host approaches have also been used to good effect for CsN03 extraction. Nitrate is a common anion found upon nitric acid extraction of 137Cs+ in the nuclear industry. Cs+ is conveniently com plexed by a large crown ether such as tetrabenzo[24] crown-8 while simple tripodal amide hosts of type 5.31 (where R is a long alkyl group to impart lipophilicity) are effective at binding N03 . Extraction efficiency of Cs+ from water into 1,2-dichloroethane was found to be enhanced by a factor of up to 4.4 in the presence of the anion host.28... 

In order to gain more direct access to these bicyclic ligands, methods have been developed which allow the formation of the macrobicycle in one step. The tripod-tripod coupling is an example of this method (Fig. 5.2) which may be performed without the need for high-dilution conditions. The synthesis of the bis-tren macrobicycle, 17, illustrates this approach.3... 

Attaching peripheral chiral R auxiliary to the amido nitrogen creates Cj-chiral tripodal amido ligands for the synthesis of chiral metal complexes. For example, the chiral zirconium chloride complex 204, obtained from the salt metathesis approach involving the reaction of the lithium salt of the trianionic ligand with ZrGI4 in toluene, contains (A)-3,3-dimethyl-2-butyl group as chiral R auxiliary.172 The peripheral chiral R auxiliaries are (.S )-1 -phenyl ethyl and (R)-l-indanyl in chiral complexes 205 and 206, respectively.173... 

Transition metal-tin bonds are the most common type of bonds after those with p-block elements, namely C, N, O, and halogens. The less common transition metal-tin bonds are associated with early transition metals, namely Ti, Zr, Flf, V, Ta, and Nb. A fundamental difficulty in this bond formation is the existence of energetically low-lying electron transfer reaction pathways from the tin to the early transition metal. An interesting approach to the synthesis of group 4 metal-tin bonds comprises the use of tripodal amido... 

The set up is now in principle ready to start an experiment. The coarse approach is carried out to position the tip close to (but not in contact with) the sample surface. Using an eyepiece, the cantilever can be viewed from the side (or alternatively one can use a top-view CCD camera for this purpose). With the eyepiece, we locate the reflection of the laser light on the cantilever and its reflection (mirror image) on the sample (red spots). Using the stepper motor, we lower the optical head until the spots are close however, we still want to clearly be able to detect a gap between the spots. In older scanner types, the optical head is lowered by using the stepper motor for one pod of a tripod, while the other two are lowered manually using the corresponding screws. In this case, it is essential that the head is lowered such that it stays leveled at all times. 

On the way to water-soluble polyether phosphines Mayer and co-workers synthesized a tripodal polyhydroxyalkylphosphine ligand in a three-step synthesis starting from the relevant hydroxyphosphine (Eq. 2) [13]. The most interesting feature of this approach is the protection of the phosphine groups as a Mo(CO)3 complex during the synthesis. 

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