Tailing drawbacks

Somewhat more complicated is the Markov chain describing the products of polycondensation with participation of asymmetric monomers. Any of them, AjSaAj, comprises a tail-to-head oriented monomeric unit Sa. It has been demonstrated [55,56] that the description of molecules of polycondensation copolymers can be performed using the Markov chain whose transient states correspond to the oriented units. A transient state of this chain ij corresponds to a monomeric unit at the left and right edge of which the groups A, and A are positioned, respectively. A state ji corresponds here to the same unit but is oriented in the opposite direction. However, a drawback of this Markov chain worthy of mention is the excessive number of its states. 

Reproducibility of monolithic columns has also been cited as a major concern because the monoliths are manufactured individually.34-35 An extensive study by Kele and Guiochon indicates that the reproducibility results of Chromolith columns were almost comparable to those from different batches of particle-packed columns.37 Other drawbacks of monolithic columns include weak reten-tivity for polar analytes,38 efficiency loss at high flow rates for larger (800 MW) molecules,39 and peak tailing, even for neutral non-ionizable compounds.36-38-40 Furthermore, silica-based monolithic... 

Computation Errors in Analyzing the Data. Probably the most serious drawback in using moments is that the tail end of the recorded curve plays too strong a role and slight errors here are magnified. However, taking the slope of the step response data is usually a rather inaccurate process also. 

Peak tailing and/or relatively broad peaks are often observed and can be a considerable drawback. In analytical applications, e.g. in the determination of enantiomeric impurities in drugs with high ee, i.e. > 98%. The poor efficiency and tailing has been explained for propranolol enantiomers by Fomstedt et al. 93] on the basis of heterogeneous mass transfer kinetics on the chiral and non-chiral adsorption sites of a cellobiohydrolase-l-based CSP. 

Some drawbacks of this packing include a strong interaction with polar analytes such as organic acids, leading to peak tailing or maybe even irreversible adsorption, and decomposition of the analyte due to chemisorbtion. On the other hand, if acid-treated alumninas are employed for the analysis of strongly acidic samples, then some of the aforementioned deleterious effects may be avoided. The analysis of basic compounds may also be used on acid-treated and neutral alumninas. 

Previous sections have already made the case for acquiring COSY data such that it may be presented in the phase-sensitive mode. The pure-absorption lineshapes associated with this provide the highest possible resolution and allow one to extract information from the fine-structure within crosspeak multiplets. However, it was also pointed out that the basic COSY-90 sequence suffers from one serious drawback in that diagonal peaks possess dispersion-mode lineshapes when crosspeaks are phased into pure absorption-mode. The broad tails associated with these can mask crosspeaks that fall close to the diagonal, so there is potential for useful information to be lost. The presence of dispersive contributions to the diagonal may be (largely) overcome by the use of the double-quantum filtered variant of COSY [37], and for this reason DQF-COSY is the experiment of choice for recording phase-sensitive COSY data. 

The only drawback to the NPA methodology is that it rests on allocating electrons to atoms through an orbital occupancy basis, not in terms of the actual locations of the electrons. The latter property is a physical observable, whereas orbital occupancy is not an observable. The NPA method does attempt to define as well as possible localized atomic orbitals, but completely localized atomic orbitals are impossible. Some electrons in an orbital centered on atom A will, in fact, be closer to atom B. Natural orbitals will have tails that penetrate zero-flux surfaces. Therefore, the NPA populations will differ from the rigorous spatially defined topological values. 

In principle, a finite GTO basis can describe neither the firee-space tail of an electronic orbital nor the nuclear cusp correctly. Because there are relatively few physically or chemically interesting properties that depend on detailed behavior of orbitals in an arbitrarily small neighborhood of a nucleus or at arbitrarily large distances from all the nuclei, the intrinsic deficiencies of a GTO basis have not proved to be a major drawback in practice. For most observables, a rich GTO basis obviates the formal limitations. More discxxssion of the long-ranged behavior issue is given below in connection with calculated work functions. 

As mentioned above, a drawback with the etalon method is that the pulses have Lorentzian-shaped frequency profiles. A better profile would be Gaussian, since Gaussians tail to zero much more quickly than Lorentzians with the same full width at half-maximum. With our shaper, we also collected... 

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