A second-order class-D audio amplifier

Class-D audio amplifiers are particularly efficient, and this efficiency has led to their ubiquity in a wide range of modern electronic appliances. Their output takes the form of a high-frequency square wave whose duty cycle (ratio of on-time to off-time) is modulated at low frequency according to the audio signal. A mathematical model is developed here for a second-order class-D amplifier design (i.e., containing one second-order integrator) with negative feedback. We derive exact expressions for the dominant distortion terms, corresponding to a general audio input signal, and confirm these predictions with simulations. We also show how the observed phenomenon of “pulse skipping” arises from an instability of the analytical solution upon which the distortion calculations are based, and we provide predictions of the circumstances under which pulse skipping will take place, based on a stability analysis. These predictions are confirmed by simulations

Circumventing the Privity Rule in Malaysia

This article briefly introduces the privity rule and its application in Malaysia which has created difficulties in relation to contracts made for the benefit of third parties. This article then investigates how Malaysian courts circumvent the privity rule to ensure that justice prevails. The mechanisms examined include among others agency, trust, tort and estoppel. This article argues that the application of these mechanisms rule are not adequate to resolve the difficulties caused by the privity rule and concludes that a statutory reform to create third party rights in contract law is required

Proteomics of Cytochrome c Oxidase-Negative versus -Positive Muscle Fiber Sections in Mitochondrial Myopathy

The mosaic distribution of cytochrome c oxidase(+) (COX+) and COX - muscle fibers in mitochondrial disorders allows the sampling of fibers with compensated and decompensated mitochondrial function from the same individual. We apply laser capture microdissection to excise individual COX+ and COX- fibers from the biopsies of mitochondrial myopathy patients. Using mass spectrometry-based proteomics, we quantify >4,000 proteins per patient. While COX+ fibers show a higher expression of respiratory chain components, COX- fibers display protean adaptive responses, including upregulation of mitochondrial ribosomes, translation proteins, and chaperones. Upregulated proteins include C1QBP, required for mitoribosome formation and protein synthesis, and STOML2, which organizes cardiolipin-enriched microdomains and the assembly of respiratory supercomplexes. Factoring in fast/slow fiber type, COX (-) slow fibers show a compensatory upregulation of beta-oxidation, the AAA(+) protease AFG3L1, and the OPA1-dependent cristae remodeling program. These findings reveal compensatory mechanisms in muscle fibers struggling with energy shortage and metabolic stress

Response of Frame Foundations to Vertical Vibrations

A series of vertical vibration tests was carried out on small lm span steel portal frames of different stiffnesses and supported on two isolated rigid circular footings on a compacted sand deposit. Dynamic loading was applied to the center of the frame and the response was monitored by means of six accelerometers attached at various locations. The resonant frequency and the maximum amplitude of vibration were observed to be dependent on the frame stiffness and two theoretical models, the combined method and the dynamic deformation method, were used to compare calculated and observed results

On the symbolic manipulation and code generation for elasto-plastic material matrices

A computerized procedure for symbolic manipulations and FORTRAN code generation of an elasto-plastic material matrix for finite element applications is presented. Special emphasis is placed on expression simplifications during intermediate derivations, optimal code generation, and interface with the main program. A systematic procedure is outlined to avoid redundant algebraic manipulations. Symbolic expressions of the derived material stiffness matrix are automatically converted to RATFOR code which is then translated into FORTRAN statements through a preprocessor. To minimize the interface problem with the main program, a template file is prepared so that the translated FORTRAN statements can be merged into the file to form a subroutine (or a submodule). Three constitutive models; namely, von Mises plasticity, Drucker-Prager model, and a concrete plasticity model, are used as illustrative examples

On the age of the magnetically active WW Psa and TX Psa members of the beta Pictoris association

There are a variety of different techniques available to estimate the ages of pre-main-sequence stars. Components of physical pairs, thanks to their strict coevality and the mass difference, such as the binary system analysed in this paper, are best suited to test the effectiveness of these different techniques. We consider the system WW Psa + TX Psa whose membership of the 25-Myr beta Pictoris association has been well established by earlier works. We investigate which age dating technique provides the best agreement between the age of the system and that of the association. We have photometrically monitored WW Psa and TX Psa and measured their rotation periods as P = 2.37d and P = 1.086d, respectively. We have retrieved from the literature their Li equivalent widths and measured their effective temperatures and luminosities. We investigate whether the ages of these stars derived using three independent techniques are consistent with the age of the beta Pictoris association. We find that the rotation periods and the Li contents of both stars are consistent with the distribution of other bona fide members of the cluster. On the contrary, the isochronal fitting provides similar ages for both stars, but a factor of about four younger than the quoted age of the association, or about 30% younger when the effects of magnetic fields are included. We explore the origin of the discrepant age inferred from isochronal fitting, including the possibilities that either the two components may be unresolved binaries or that the basic stellar parameters of both components are altered by enhanced magnetic activity. The latter is found to be the more reasonable cause, suggesting that age estimates based on the Li content is more reliable than isochronal fitting for pre-main-sequence stars with pronounced magnetic activity.Comment: Accepted by Astronomy and Astrophysics on December 13, 2016. 13 pages and 11 figure

Mechanistic and pathological study of the genesis, growth, and rupture of abdominal aortic aneurysms

Postprint (published version