Structure current limitations

Although comparative modeling is the most accurate modeling approach, it is limited by its absolute need for a related template structure. For more than half of the proteins and two-thirds of domains, a suitable template structure cannot be detected or is not yet known [9,11]. In those cases where no useful template is available, the ab initio methods are the only alternative. These methods are currently limited to small proteins and at best result only in coarse models with an RMSD error for the atoms that is greater than 4 A. However, one of the most impressive recent improvements in the field of protein structure modeling has occurred in ab initio prediction [155-157]. 

The intermetallic alloy NiAl is discussed as a potential base alloy for high temperature structural materials. Its use is currently limited by low room temperature ductility and fracture toughness. Consequently, substantial research efforts have been directed towards understanding its mechanical behaviour [1, 2] so that detailed experimental [3, 4, 5] and theoretical [6, 7, 8] analyses of the deformation of NiAl are available today. 

If one of the structures to be bonded is the sheath or metallic armouring of an electric supply cable, special precautions will be necessary to ensure that the voltage rise at the bond in the event of an instantaneous earth fault on the power-supply system does not endanger personnel or equipment associated with other buried structures. The bond and any associated current-limiting device should be suitably insulated and of adequate current-carrying capacity. 

While other programs require modification of the actual code in changing the polymer, spectra, or model, only changes in the user database is required here. Changes in the program since a brief report (22) in 1985 include improvement of the menu structure, added utilities for spectral manipulations, institution of demo spectra and database. Inclusion of Markov statistics, and automation for generation of the coefficients in Equation 1. Current limitations are that only three models (Bernoul llan, and first- and second-order Markov) can be applied, and manual input Is required for the N. A. S. L.. 

In contrast, the number of known structures of homoleptic, monomeric two-coordinate amides of cadmium is currently limited to just one example. The structure of the compound [Cd N(SiMe3)2 2] has been determined by electron diffraction and the data showed that it has a linear NCdN skeleton with a Cd—N bond length of 2.03(2) A. It is clear, however, that several other homoleptic cadmium amides (known and others as yet not synthesized) can be predicted to have monomeric structures in the solid state. For example Cd NMR studies of amides such as [Cd N(SiMe3)2 2] or [Cd N(SiMe2Ph)2 2] indicate that they are... 

With PSPIs, the photopatterning process involves significantly fewer process steps (Figure 19) and eliminates the need for expensive plasma equipment. However, the process is currently limited to aspect ratios of about 0.5 for negative features such as via holes. Higher aspect ratios can be obtained for positive features such as lines unfortunately, holes are the more-prevalent features for TFML structures. 

There are three current theories on sulfiding the CoMo/Al catalyst monolayer, intercalation, and contact synergism. These are schematically depicted in Fig. 4. All start with the assumption of a monolayer model for the oxidized catalyst, differences appearing in the subsequent effect that sulfiding has on the monolayer structure. Space limitations preclude a full description of these models the original references should be consulted for more detail. 

The photonic force microscope may yield a means for proximal probe imaging within fluid-containing voids and structures such as vesicles and living cells. Some current limitations of the photonic force microscope include the potential for incorporation of optical artifacts when internal structures of optically complex samples (such as cells) are to be studied. Coupling of optical features into the images of such a microscope arises via the dependence of the optical trapping... 

Three dimensional packed bed electrodes are generally considered for reactions which operate with low current densities in order to increase localized mass transfer rates and/or increase overall current per unit cell volume. The maximum current density at any position in the electrode structure is limited by the prevailing conditions of mass transfer. The limiting current thus can also have... 

It should be noted here that, currently, characterization, separation, and purification techniques of the larger cascades or dendrimers (previously discussed in earlier chapters) are straining the limits of present instrumentation. Thus, unequivocal characterization of dendritic networks is currently limited and will necessitate the development of new methods and instrumentation. However, dendritic network structural verification and elucidation should be facilitated by integration of known standard materials science methods, e.g., MS and EM. 

Although such nanotubes form an interesting structure with potential for exterior functionalization, they are currently limited to passive transport/ release of molecules in the interior. Future work may focus on using non-canonical amino acids to impart functionalizable interior surfaces to allow orthogonal functionalization of the interior and exterior surfaces (ten Cate et al., 2006). 

It is clear that CD measurements can provide unique information which can be used to design and optimize the separation of structurally complex, biologically active materials. However, the fact that HPLC is a time dependent experiment, and the time dependence of the analyte distribution is not compatible with the scanning rate of conventional CD instruments currently limits the CD-HPLC measurement to a single wavelength. This problem will be solved if multichannel detection can be effectively coupled to the CD experiment. 

With the advent of the genome projects, it now becomes possible to explore how nature has achieved functional diversity from a limited set of structural types by examining structure-function relationships in protein superfamilies. Our ability to do this at a sophisticated level is currently limited by the relatively small number of fold classes that have been structurally characterized, but recent initiatives to determine many more three-dimensional structures can be expected to substantially address this deficit over the next few years (Sali, 1998). 

A number of recently developed methods offer the potential for improving the quality of NMR structures and for increasing the size of proteins that will be examined. In particular, the use of residual dipolar couplings and of anisotropic contributions to relaxation provide new kinds of restraints that promise to lead to more accurate NMR structures.78 80 The recently developed TROSY (transverse relaxation optimized spectroscopy) method81 exploits relaxation phenomena to produce spectra with narrow lines, and promises to significantly expand the size of protein targets that can be examined by NMR from the current limit of 35 kDa to perhaps 150 kDa. 

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