87,896 research outputs found
Density modulo 1 of a sequence associated to some multiplicative functions evaluated at polynomial arguments
No full textWe study density modulo 1 of the sequence with general term ∑ m≤n f (G(m)) where f is the strongly multiplicative function of the form f (n) = ∏ p|n (1 − ν(p) p) and ν is a multiplicative function for which there exists a real number 0 < r ≤ 1 such that 1 ≤ |ν(p)| ≤
Pseudo-shock waves and their interactions in high-speed intakes
No full textIn an air-breathing engine the flow deceleration from supersonic to subsonic conditions takes places inside the isolator through a gradual compression consisting of a series of shock waves. The wave system, referred to as a pseudo-shock wave or shock train, establishes the combustion chamber entrance conditions, and therefore influences the performance of the entire propulsion system. The characteristics of the pseudo-shock depend on a number of variables which make this flow phenomenon particularly challenging to be analysed. Difficulties in experimentally obtaining accurate flow quantities at high speeds and discrepancies of numerical approaches with measured data have been readily reported. Understanding the flow physics in the presence of the interaction of numerous shock waves with the boundary layer in internal flows is essential to developing methods and control strategies. To counteract the negative effects of shock wave/boundary layer interactions, which are responsible for the engine unstart process, multiple flow control methodologies have been proposed. Improved analytical models, advanced experimental methodologies and numerical simulations have allowed a more in-depth analysis of the flow physics. The present paper aims to bring together the main results, on the shock train structure and its associated phenomena inside isolators, studied using the aforementioned tools. Several promising flow control techniques that have more recently been applied to manipulate the shock wave/boundary layer interaction are also examined in this review
H-index és kutatói értékelés: Egy lehetséges, átfogó, szerzői szintű értékelési mutató komponensei (Szemletanulmány)
No full textNorouzi, A., Parsaei-Mohammadi, P., Zare-Farashbandi, F., Zare-Farashbandi,E., Geraei, E. (2024) H-index and research evaluation: A suggested set of components for developing a comprehensive author-level index, Journal of Information Science. https://doi.org/10.1177/0165551524129376
Dark matter spike around Bumblebee black holes
No full textThe effects of dark matter spike in the vicinity of the supermassive black
hole, located at the center of M87 (the Virgo A galaxy), are investigated
within the framework of the so-called Bumblebee Gravity. Our primary aim is to
determine whether the background of spontaneous Lorentz symmetry breaking has a
significant effect on the horizon, ergo-region, and shadow of the Kerr
Bumblebee black hole in the spike region. For this purpose, we first
incorporate the dark matter distribution in a Lorentz-violating spherically
symmetric space-time as a component of the energy-momentum tensors in the
Einstein field equations. This leads to a space-time metric for a Schwarzschild
Bumblebee black hole with a dark matter distribution in the spike region and
beyond. Subsequently, this solution is generalized to a Kerr Bumblebee black
hole through the use of the Newman-Janis-Azreg-A\"inou algorithm. Then,
according to the available observational data for the dark matter spike density
and radius, and the Schwarzschild radius of the supermassive black hole in
Virgo A galaxy, we examine the shapes of shadow and demonstrate the influence
of the spin parameter , the Lorentz-violating parameter and the
corresponding dark matter halo parameters and on the
deformation and size of the shadow.Comment: accepted for publication in JCA
Inclusion of different blends of poultry processed proteins in practical diets for African catfish (Clarias gariepinus) reared in RAS: Effects on nutrient digestibility, growth performance and fillet quality
No full textThe present study aimed to test the effects of different dietary inclusion levels of fishmeal (F) and blends of poultry processed protein meals (P), i.e. poultry by-product meal, hydrolysed feather meal, dry-blood meal in African catfish (Clarias gariepinus). Fish were fed during 84 days with four practical diets, i.e. diet HF-LP (F: 90 g kg − 1 ; P: 227 g kg − 1), diet MF-MP (F: 45 g kg − 1 ; P: 280 g kg − 1), diet HF-HP (F: 90 g kg − 1 ; P: 315 g kg − 1), and diet LF-HP (F: 10 g kg − 1 ; P: 392 g kg − 1). Fish fed diet LF-HP showed the lowest protein and lipid digestibility coefficients (82 % and 92 % vs. 84 % and 94 %, respectively; p<0.05) compared to fish fed the other diets, and the worst performance in terms of final body weight (551 g vs. 673 g), feed intake (247 g d − 1 vs. 301 g d − 1), condition factor (0.83 vs. 0.86), specific growth rate (2.69 % d − 1 vs. 3.14 % d − 1), and feed conversion ratio (1.34 vs. 1.11) (p<0.001). Fish fed diet MF-MP reported the highest survival rate compared to other diets (96.8 % vs. 94.5 %; p<0.001). Fish fed diets with the highest inclusion rates of poultry by-product meal (140 g kg − 1 or 165 g kg − 1) and hydrolysed feather meal (125 g kg − 1 or 135 g kg − 1) were associated with the lowest fillet yield (46.2 % vs. 47.1 %) respect to fish fed the other diets (p<0.05). In conclusion, a diet with 10 g kg − 1 of fishmeal and 392 g kg − 1 of a blend of poultry processed animal proteins is not suitable to sustain the performance of African catfish, whereas a diet with a minimum content of fishmeal at 45 g kg − 1 and a blend of poultry processed animal proteins at about 280 g kg − 1 could be technically and economically attractive for the RAS farming of this species
Effect of back-pressure forcing on shock train structures in rectangular channels
No full textThe deceleration of a supersonic flow to the subsonic regime inside a high-speed engine occurs through a series of shock waves, known as a shock train. The generation of such a flow structure is due to the interaction between the shock waves and the boundary layer inside a long and narrow duct. The understanding of the physics governing the shock train is vital for the improvement of the design of high-speed engines and the development of flow control strategies. The present paper analyses the sensitivity of the shock train configuration to a back-pressure variation. The complex characteristics of the shock train at an inflow Mach number M = 2 in a channel of constant height are investigated with two-dimensional RANS equations closed by the Wilcox k-ω turbulence model. Under a sinusoidal back-pressure variation, the simulated results indicate that the shock train executes a motion around its mean position that deviates from a perfect sinusoidal profile with variation in oscillation amplitude, frequency, and whether the pressure is first increased or decreased
Experimental investigation on shock wave diffraction over sharp and curved splitters
No full textShock wave diffraction occurs when a normal travelling wave passes through a sudden area expansion. Turbulent, compressible, and vortical are the characterising adjectives that describe the flow features, which are slowly smeared out due to the dissipative nature of turbulence. The study of this phenomenon provides insight into several flow structures such as shear layer formation, vortex development, and vortex/shock interaction whose applications include noise control, propulsion or wing aerodynamics. A large amount of research has been carried out in the analysis of shock wave diffraction mainly around sharp wedges, but only few studies have considered rounded corners. This project has the aim to examine and compare the flow features which develop around three different geometries, ramp, symmetric and rounded, with experimental incident shock Mach numbers of 1.31 and 1.59, and Reynolds numbers of 1.08x106 and 1.68x106. Schlieren photography is used to obtain qualitative information about the evolution of the flow field. The results show that ramp and symmetrical wedges with a tip angle of 172° behave in the same manner, which exhibit clear dissimilarities with a curved corner. The flow field evolves more rapidly for a higher incoming Mach number which is also responsible for the development of stronger structures
Numerical investigation on three-dimensional shock train structures in rectangular isolators
No full textThe understanding of the formation of shock trains in high-speed engines is vital for the improvement of engine design. The formation of these flow structures in a narrow duct, driven by the presence of the viscous effects on the walls, is an extremely complex process that is not fully understood. This investigation demonstrates the high sensitivity of the shock train to the solving equations. The establishment of the shock train in the duct mainly depends on the way that the boundary layer develops on the walls. The - Wilcox model confirms to be the most suitable to accurately reproduce the subtle features close to the solid boundary. The assumption of two-dimensional flow is not completely accurate for describing internal flows where the three-dimensional effects from the shock wave/boundary layer interactions cannot be neglected. The centreline flow properties show that the first shock wave has the same strength in the two- and three-dimensional cases. However, in the three-dimensional case the thinner boundary layer behind the leading shock allows the flow to expand more in the subsonic region causing a stronger deceleration of the flow behind the first shock
Upconverting nanoengineered Surfaces: maskless photolithography for security applications
No full textThe deceleration of a supersonic flow to the subsonic regime inside a high-speed engine occurs through a series of shock waves, known as a shock train. The generation of such a flow structure is due to the interaction between the shock waves and the boundary layer inside a long and narrow duct. The understanding of the physics governing the shock train is vital for the improvement of the design of high-speed engines and the development of flow control strategies. The present paper analyses the sensitivity of the shock train configuration to a back-pressure variation. The complex characteristics of the shock train at an inflow Mach number M = 2 in a channel of constant height are investigated with two-dimensional RANS equations closed by the Wilcox k-ω turbulence model. Under a sinusoidal back-pressure variation, the simulated results indicate that the shock train executes a motion around its mean position that deviates from a perfect sinusoidal profile with variation in oscillation amplitude, frequency, and whether the pressure is first increased or decreased.<br/
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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