Exploring the tilted accretion disc of AQ Men with TESS

ABSTRACT AQ Men is a nova-like variable that is presumed to have a tilted, precessing accretion disc. Grazing eclipses in this system have been speculated to be useful in exploring the geometry of its accretion disc. In this work, we analysed Transiting Exoplanet Survey Satellite (TESS) observations of AQ Men, which provide the best light curve of this object thus far. We show that the depths of the eclipses are changing with the orientation of the accretion disc, which means that they can serve as a direct test of the tilted accretion disc models. The precession period of the accretion disc is increasing during the TESS observations. However, it is still shorter than the period determined in the previous studies. The amplitude of the variability related to the precession of the accretion disc varies, and so does the shape of this variability. Moreover, we have detected a positive superhump that was previously unseen in AQ Men. Interestingly, the positive superhump has a strongly non-sinusoidal shape, which is not expected for a nova-like variable.

Current Interactions Mitigation in 3-Phase PFC Modular Rectifier through Differential-Mode Choke Filter Boost Converter

In this paper, a new way to mitigate the current interactions is proposed. The problem of current interactions arises when a modular three-phase (3-phase) rectifier (three single-phase modules) with boost converter for power factor correction (PFC) is used. A new differential-mode choke filter is implemented in the developed boost converter. The choke here is a specially made differential inductor in the input of the boost converter that eliminates the known current interactions. To prove the new concept, a study of the level of mitigation of the current interactions is presented. The control is operated in continuous driving mode (CCM), and the popular UC3854B circuit was used for this. The rectifier proposal is validated through a set of simulations performed on the PSIM 12.0 platform, as well as the construction of a prototype. With the results obtained, it is confirmed that the differential-mode choke filter eliminates the current interactions. It is observed that at the input of the rectifier, a sinusoidal alternating current with a low level of harmonic distortion is consumed from the grid. The sinusoidal shape of the phase current proves that a better power factor capable of meeting the international standards is obtained, and that the circuit in its initial version is operational. This proven result promises a good PFC operation, to guarantee the better quality of the electrical energy, being able to be applied in systems that require a high PFC, e.g., in battery charging, wind systems, or in aeronautics and spacecrafts.

Gas flow through a bore-piston ring contact

This work reports on the derivation of simplified but accurate models to describe gas flow through a bore-piston ring contact in reciprocating machines like compressors or IC engines. On the basis of the aperture field of a contact deduced from real measurements carried out on an expanding ring in a bore, a scale analysis on the complete compressible flow model is performed, assuming ideal gas law. It is shown that the flow can be treated as stationary and three distinct flow regimes can be identified (namely incompressible, compressible creeping, and compressible inertial regimes). Three dimensionless parameters characterizing these regimes are identified. While for the two former regimes, classical analytical Poiseuille type of models are derived, an Oseen approximation is further employed for the latter, yielding a quasi-analytical solution. The models are successfully compared to direct numerical simulations (DNS) of the complete initial set of balance equations in their steady form performed on an aperture field of sinusoidal shape. These simplified models are of particular practical interest since they allow an accurate gas flow-rate estimate through a real contact using the aperture field as the geometrical input datum, together with the thermodynamic conditions (pressure and temperature). This represents an enormous advantage as DNS is still very challenging in practice due to the extremely small value of the contact aperture to contact length ratio.

A high performance grid connected PV system based on HERIC transformerless inverter

<p>This paper presents an effective single phase grid connected photovoltaic PV system based on High Efficiency and Reliable Inverter Concept HERIC transformerless inverter. dc-dc boost converter controlled by incremental conductance IC maximum power point tracker MPPT is employed to achieve the maximum extraction power of the PV panels. Proportional integral PI controller controls the output voltage of the boost converter to meet the utility grid requirements. LCL filter is utilized to keep the inverter voltage very close to sinusoidal shape. Employing the HERIC transformerless inverter reduces significantly the ground leakage current beyond safe limits. Semiconductors losses are studied to investigate the efficiency of the proposed system at different insolation levels. Simulation results verify the high performance of the proposed system when considering leakage current and system efficiency.</p>

Modeling transient vibration-sound generation processes

In this paper, a problem of sound generation of two-blade rotor sinusoidal shape during helicopter landing is solved. Near and far sound field characteristics have been calculated. A comparative analysis of obtained numerical results with results for Mach number 0.2<M<0.4 is given. In particular noticed, that for a low Mach’s number M<0.1 transitional mode can occurs, which produces a blade flutter as a result.

A Josephson junction based on a highly disordered superconductor/low-resistivity normal metal bilayer

We calculate the current–phase relation (CPR) of a SN-S-SN Josephson junction based on a SN bilayer of variable thickness composed of a highly disordered superconductor (S) and a low-resistivity normal metal (N) with proximity-induced superconductivity. In such a junction, the N layer provides both a large concentration of phase in the weak link and good heat dissipation. We find that when the thickness of the S and the N layer and the length of the S constriction are about the superconducting coherence length the CPR is single-valued and can be close to a sinusoidal shape. The product I c R n can reach Δ(0)/2|e| (I c is the critical current of the junction, R n is its normal-state resistance, Δ(0) is the superconductor gap of a single S layer at zero temperature). Our calculations show, that the proper choice of the thickness of the N layer leads both to nonhysteretic current–voltage characteristics even at low temperatures and a relatively large product I c R n.

A New Asymmetrical MLI with Reduced Switch Count for a Three Phase Induction Motor

This work explores a novel multilevel inverter (MLI) topology to minimize the number of power switches in the passage of current to accomplish each level of the output voltage. The unequal magnitudes of the dc voltage sources in attempt to realize higher levels of the output voltage bring in the asymmetrical nature of operation. It involves a series parallel switched configuration with bidirectional switches to avert the flow of circulating current in between the two H - bridges in each phase of the MLI. The effort incites to use the theory of a new Pulse Width Modulation (PWM) strategy for mitigating the higher frequency components of the voltage applied to the stator. It imbibes the Phase Disposition (PD) principles in the modulating strategy for arriving at the sinusoidal shape for the output voltage . Total Harmonic Distortion (THD) indexed by lower values for the output voltage over the traditional firing scheme serves to be the highlight for the MLI in acclaiming its place in the inverter world. The results obtained through MATLAB based simulation over a range of modulation indices. The performance measured in terms of the THD claims its suitability for use in Induction Motor (IM) drives.

Critical view of the concept of sequence stratigraphy

Based on a theoretical analysis, the main shortcomings of modern varieties of the concept of sequence stratigraphy are shown: they do not comply with the definition of the relative sea level, which is given by the authors themselves; the nature of tectonic immersion, which cannot have a sinusoidal shape, is not taken into account; the boundaries of sequences, identified as subaerial disagreements on the periphery of the cover, are unlawfully compared with consonant boundaries within the basins. The need for a thorough review of this concept based on the new basic provisions is shown.

Effect of the spatial variation of permeability on air bubble creation and compression

Tow bundles inside a quasi-unidirectional non-crimp fabric are maintained by sewing threads that induce variation in the bundles’ shape. Indeed, the sewing threads apply a light clamping force that gives a periodical and sinusoidal shape to the tow’s cross-sectional area. This tow cross-sectional area heterogeneity, as a function of position in the fabric, induces a variation of the permeability values. Consequently, while injecting liquid into the fibrous bed, preform's impregnation is influenced as well as the fabric’s void content. The aim of this paper is to consider the effect of tow cross-sectional area heterogeneity on the quality of the manufactured composite part. It leads to reveal the influence of the fibrous reinforcement’s microstructure on the air bubble creation and compression phenomena, especially in terms of process time and the micro and macro air bubble distribution.

Dynamic moisture sorption and dimensional stability of furfurylated wood with low lignin content

Degradation of lignin occurs naturally in wood due to the influence of microorganisms or photic radiation. To improve the properties of wood with low lignin content, furfuryl alcohol (FA) at the concentration of 25% was used to modify poplar wood (Populus euramericana Cv.) after partial delignification. Moisture sorption and dimensional stability of the samples were investigated under dynamic conditions where the relative humidity (RH) was changed sinusoidally between 45% and 75% at 25°C. Both the moisture content (MC) and the tangential dimensional change varied with a sinusoidal shape similar to the RH. Hygroscopicity and hygroexpansion increased after delignification, while furfurylation led to an inverse impact by reducing MC, dimensional changes, amplitudes of MC and dimensional changes, moisture sorption coefficient (MSC), and humidity expansion coefficient (HEC). After delignification and further furfurylation, the MC and the dimensional changes were reduced by about 20%, and the maximum drop in amplitudes of MC and dimensional changes was about 30%, while the MSC and the HEC decreased by over 15%. In addition, the furfurylated wood with low lignin content exhibited lower sorption hysteresis and swelling hysteresis.