Recent Advances in Stereochemistry Reveal Classification Shortcomings

We contend that the Polytope model utilized by IUPAC to specify stereoisomerism for species ML<i>_n</i> with <i>n</i> > 3 should be universally applied. Such application recently led to the synthesis of isolable compounds displaying a new fundamental form of isomerism, akamptisomerism, pertinent to ML₂ stereocenters. We review 443807 molecules that could be classified as akamptisomers. Some akamptisomers are described as being “wrong” by existing IUPAC rules, hindering molecular conception. For many classes of medicinal and technology-related molecules, software packages like ChemDraw mostly do not handle akamptisomers correctly, databases such as CAS provide 2D representations inconsistent with those presented in the original publications, and often the akamptisomeric identity of compounds remains unknown. These features hinder both human and machine-learning approaches to chemical design. Further, the existence of previously unrecognized isomeric forms has broad implications for patents and pharmaceutical-registration requirements. Hence, the immediate re-examination of stereochemistry is demanded.

Recent Advances in Stereochemistry Reveal Classification Shortcomings

We contend that the Polytope model utilized by IUPAC to specify stereoisomerism for species ML<i>_n</i> with <i>n</i> > 3 should be universally applied. Such application recently led to the synthesis of isolable compounds displaying a new fundamental form of isomerism, akamptisomerism, pertinent to ML₂ stereocenters. We review 443807 molecules that could be classified as akamptisomers. Some akamptisomers are described as being “wrong” by existing IUPAC rules, hindering molecular conception. For many classes of medicinal and technology-related molecules, software packages like ChemDraw mostly do not handle akamptisomers correctly, databases such as CAS provide 2D representations inconsistent with those presented in the original publications, and often the akamptisomeric identity of compounds remains unknown. These features hinder both human and machine-learning approaches to chemical design. Further, the existence of previously unrecognized isomeric forms has broad implications for patents and pharmaceutical-registration requirements. Hence, the immediate re-examination of stereochemistry is demanded.

Form Defects Consideration in Polytope-Based Tolerance Analysis

The polytope-based tolerance analysis in design process uses a finite set of constraints to represent specifications and propagates these constraints to any objective point in the Euclidean space. The operations of Minkowski sum and intersection on polytopes are well suited to serial and parallel assemblies. The polytope model has been applied to complex assemblies which contain a large number of joints and geometrical tolerances. However, the previous studies on this model consider toleranced features as surfaces of perfect form. The ignorance of form defects in tolerance analysis would result in a significant loss in accuracy and reliability. In this paper, an extension of the polytope model for tolerance analysis considering form defects is described in which the skin model shape representing the physical shape of the product is adopted to simulate the actual toleranced feature in place of the substitute one used conventionally. The combination of polytope model and skin model shape is expected to inherit many of the advantages of each model, combining easy-to-use tolerance propagation and form defects representation with accuracy guarantees. To demonstrate the method and its respective application, a case study of an assembly is illustrated in detail. The proposed method further enhances the capability of the polytope model in handling form defects and provides more realistic assembly results that approximate the actual assembly conditions for design evaluation.

Uncertain DC-DC Zeta Converter Control in Convex Polytope Model Based on LMI Approach

<span>A dc-dc zeta converter is a switch mode dc-dc converter that can either step-up or step-down dc input voltage. In order to regulate the dc output voltage, a control subsystem needs to be deployed for the dc-dc zeta converter. This paper presents the dc-dc zeta converter control. Unlike conventional dc-dc zeta converter control which produces a controller based on the nominal value model, we propose a convex polytope model of the dc-dc zeta converter which takes into account parameter uncertainty. A linear matrix inequality (LMI) is formulated based on the linear quadratic regulator (LQR) problem to find the state-feedback controller for the convex polytope model. Simulation results are presented to compare the control performance between the conventional LQR and the proposed LMI based controller on the dc-dc zeta converter. Furthermore, the reduction technique of the convex polytope is proposed and its effect is investigated.</span>

MRAC Control with Prior Model Knowledge for Asymmetric Damaged Aircraft

This paper develops a novel state-tracking multivariable model reference adaptive control (MRAC) technique utilizing prior knowledge of plant models to recover control performance of an asymmetric structural damaged aircraft. A modification of linear model representation is given. With prior knowledge on structural damage, a polytope linear parameter varying (LPV) model is derived to cover all concerned damage conditions. An MRAC method is developed for the polytope model, of which the stability and asymptotic error convergence are theoretically proved. The proposed technique reduces the number of parameters to be adapted and thus decreases computational cost and requires less input information. The method is validated by simulations on NASA generic transport model (GTM) with damage.