A self excitation and control system for wind tunnel dynamic stability measurements

The paper describes the design and development of a fast acting self-excitation and control system based on the principles of regenerative and negative feedback for phase resonance testing of aerodynamic models in wind tunnels. Simulation tests and analyses using a linearized model of the drive system are carried out, and results indicate that the system would function even if the system damping becomes neutral or negative. Experiments for dynamic stability measurements show that the control system meets all specifications and performs satisfactorily even in the presence of moderate amounts of turbulence in the air flow

Noncommutative generalizations of theorems of Cohen and Kaplansky

This paper investigates situations where a property of a ring can be tested on a set of "prime right ideals." Generalizing theorems of Cohen and Kaplansky, we show that every right ideal of a ring is finitely generated (resp. principal) iff every "prime right ideal" is finitely generated (resp. principal), where the phrase "prime right ideal" can be interpreted in one of many different ways. We also use our methods to show that other properties can be tested on special sets of right ideals, such as the right artinian property and various homological properties. Applying these methods, we prove the following noncommutative generalization of a result of Kaplansky: a (left and right) noetherian ring is a principal right ideal ring iff all of its maximal right ideals are principal. A counterexample shows that the left noetherian hypothesis cannot be dropped. Finally, we compare our results to earlier generalizations of Cohen's and Kaplansky's theorems in the literature.Comment: 41 pages. To appear in Algebras and Representation Theory. Minor changes were made to the numbering system, in order to remain consistent with the published versio

Gorenstein homological algebra and universal coefficient theorems

We study criteria for a ring—or more generally, for a small category—to be Gorenstein and for a module over it to be of finite projective dimension. The goal is to unify the universal coefficient theorems found in the literature and to develop machinery for proving new ones. Among the universal coefficient theorems covered by our methods we find, besides all the classic examples, several exotic examples arising from the KK-theory of C*-algebras and also Neeman’s Brown–Adams representability theorem for compactly generated categories

The Recursive Record Semantics of Objects Revisited

In a call-by-value language, representing objects as recursive records requires using an unsafe fixpoint. We design, for a core language including extensible records, a type system which rules out unsafe recursion and still supports the reconstruction of a principal type. We illustrate the expressive power of this language with respect to object-oriented programming by introducing a sub-language for «mixin-based» programming

Repaired tetralogy of Fallot: the roles of cardiovascular magnetic resonance in evaluating pathophysiology and for pulmonary valve replacement decision support

Surgical management of tetralogy of Fallot (TOF) results in anatomic and functional abnormalities in the majority of patients. Although right ventricular volume load due to severe pulmonary regurgitation can be tolerated for many years, there is now evidence that the compensatory mechanisms of the right ventricular myocardium ultimately fail and that if the volume load is not eliminated or reduced by pulmonary valve replacement the dysfunction might be irreversible. Cardiovascular magnetic resonance (CMR) has evolved during the last 2 decades as the reference standard imaging modality to assess the anatomic and functional sequelae in patients with repaired TOF. This article reviews the pathophysiology of chronic right ventricular volume load after TOF repair and the risks and benefits of pulmonary valve replacement. The CMR techniques used to comprehensively evaluate the patient with repaired TOF are reviewed and the role of CMR in supporting clinical decisions regarding pulmonary valve replacement is discussed

Identification of the Aerodynamic Model of the DLR Research Aircraft ATTAS from Flight Test Data.

Determination of the aerodynamic characteristics of the ATTAS aircraft from flight test data is of considerable importance for many of the research projects pursued at the DLR. The report provides the details of flight tests carried out for this purpose. The data checking is based on the kinematic equations of aircraft motion. The estimation of aerodynamic derivatives is carried out from the coupled equations of aircraft motion. For both of these purposes the maximum likelihood estimation method is employed. The details of mass characteristics data are provided along with other aircraft installation-dependent data required for a parameter estimation. The report provides the results of kinematic consistency checking and the aerodynamic derivatives at typical flight conditions, and attempts to derive a combined model valid over a wider range of speed variations

Identification of the Aerodynamic Model of the DLR Research Aircraft ATTAS from Flight Test Data.

Determination of the aerodynamic characteristics of the ATTAS aircraft from flight test data is of considerable importance for many of the research projects pursued at the DLR. The report provides the details of flight tests carried out for this purpose. The data checking is based on the kinematic equations of aircraft motion. The estimation of aerodynamic derivatives is carried out from the coupled equations of aircraft motion. For both of these purposes the maximum likelihood estimation method is employed. The details of mass characteristics data are provided along with other aircraft installation-dependent data required for a parameter estimation. The report provides the results of kinematic consistency checking and the aerodynamic derivatives at typical flight conditions, and attempts to derive a combined model valid over a wider range of speed variations