Travelling-waves consistent with turbulence-driven secondary flow in a square duct

We present numerically determined travelling-wave solutions for pressure-driven flow through a straight duct with a square cross-section. This family of solutions represents typical coherent structures (a staggered array of counter-rotating streamwise vortices and an associated low-speed streak) on each wall. Their streamwise average flow in the cross-sectional plane corresponds to an eight vortex pattern much alike the secondary flow found in the turbulent regime

Direct numerical simulation of the flow around an aerofoil in ramp-up motion

A detailed analysis of the flow around a NACA0020 aerofoil at Rec = 2 × 104 undergoing a ramp up motion has been carried out by means of direct numerical simulations. During the manoeuvre, the angle of attack is linearly varied in time between 0° and 20° with a constant rate of change of αrad = 0.12 U∞/c. When the angle of incidence has reached the final value, the lift experiences a first overshoot and then suddenly decreases towards the static stall asymptotic value. The transient instantaneous flow is dominated by the generation and detachment of the dynamic stall vortex, a large scale structure formed by the merging of smaller scales vortices generated by an instability originating at the trailing edge. New insights on the vorticity dynamics leading to the lift overshoot, lift crisis, and the damped oscillatory cycle that gradually matches the steady condition are discussed using a number of post-processing techniques. These include a detailed analysis of the flow ensemble average statistics and coherent structures identification carried out using the Q-criterion and the finite-time Lyapunov exponent technique. The results are compared with the one obtained in a companion simulation considering a static stall condition at the final angle of incidence α = 20°

Home Sweet Home: The Impact of Lifestyle on a Cat’s Approach to Impossible Tasks in the Home Environment

: Cat welfare is a topic of growing interest in the scientific literature. Although previous studies have focused on the effects of living style (i.e., indoor/outdoor) on cat welfare, there has been a noticeable dearth of analysis regarding the impact of lifestyle on cats' inclination and mode of communication with humans. Our research aimed to analyze the possible effect of lifestyle (e.g., living indoors only or indoor/outdoor) on cat-human communication. The cats were tested using the impossible task paradigm test, which consists of some solvable trials in which the subject learns to obtain a reward from an apparatus, followed by an impossible trial through blocking the apparatus. This procedure triggers a violation of expectations and is considered a useful tool for assessing both the decision-making process and the tendency to engage in social behaviors towards humans. A specific ethogram was followed to record the behavioral responses of the cats during the unsolvable trial. Our results show the effects of lifestyle and age on domestic cats, providing valuable insights into the factors that influence their social behaviors. Cats that can roam freely outdoors spent less time interacting with the apparatus compared to indoor-only cats. Additionally, roaming cats showed stress behaviors sooner following the expectancy of violation compared to indoor cats. The lifestyle of cats can influence their problem-solving approach while not affecting their willingness to interact with humans or their overall welfare. Future studies on this topic can be useful for improving the welfare of domestic cats

Immersed boundary method for generalised finite volume and finite difference Navier-Stokes solvers

In Immersed Boundary Methods (IBM) the effect of complex geometries is introduced through the forces added in the Navier-Stokes solver at the grid points in the vicinity of the immersed boundaries. Most of the methods in the literature have been used with Cartesian grids. Moreover many of the methods developed in the literature do not satisfy some basic conservation properties (the conservation of torque, for instance) on non-uniform meshes. In this paper we will follow the RKPM method originated by Liu et al. [1] to build locally regularized functions that verify a number of integral conditions. These local approximants will be used both for interpolating the velocity field and for spreading the singular force field in the framework of a pressure correction scheme for the incompressible Navier-Stokes equations. We will also demonstrate the robustness and effectiveness of the scheme through various examples

Localized turbulence structures in transitional rectangular-duct flow

Direct numerical simulations of transitional flow in a rectangular duct of cross-sectional aspect ratio A≡s/h=1–9 (s and h being the duct half-span and half-height, respectively) have been performed in the Reynolds number range Re≡ubh/ν=650–1500 (ub and ν being the bulk velocity and the kinematic viscosity, respectively) in order to investigate the dependence on the aspect ratio of spatially localized turbulence structures. It was observed that the lowest Reynolds number ReT, estimated in a specific way, for localized (transiently sustaining) turbulence decreases monotonically from ReT=730 for A=1 (square duct) with increasing aspect ratio, and for A=5 it nearly attains a minimal value ReT≈670 that is consistent with the onset Reynolds number of turbulent spots in a plane channel (A=∞). Turbulent states consist of localized structures that undergo a fundamental change around A=4. At Re=ReT turbulence for A=1–3 is streamwise-localized similar to turbulent puffs in pipe flow, while for A=5–9 turbulence at Re=ReT is also localized in the spanwise direction, similar to turbulent spots in plane channel flow. This structural change in turbulent states at Re=ReT is attributed to the exclusion of turbulence from the vicinity of the duct sidewalls in the case of a wide duct with A≳4: here the friction length on the sidewalls is so long that the size (around 100 times the friction length) of a self-sustaining minimal flow unit of streamwise vortices and streaks is larger than the duct height and, therefore, it cannot be accommodated

Puppies in the problem-solving paradigm: quick males and social females

We report an observational, double-blind study that examined puppies’ behaviors while engaged in solving an experimental food retrieval task (food retrieval task instrument: FRTI). The experimental setting included passive social distractors (i.e., the dog’s owner and a stranger). The focus was on how the social and physical environment shapes puppies’ behaviors according to sex. The dependent variables were the number of tasks solved on an apparatus (Performance Index) and the time required to solve the frst task (Speed). Sex and Stress were set as explanatory factors, and Social Interest, FRTI interactions, other behavior, and age as covariates. The main fndings were that male puppies solved the frst task faster than females. On the other hand, females displayed signifcantly more social interest and did so more rapidly than males. Males showed delayed task resolution. This study demonstrates sex diferences in a problem-solving task in dog puppies for the frst time, thus highlighting that sexually dimorphic behavioral diferences in problem-solving strategies develop early on during ontogenesis.info:eu-repo/semantics/publishedVersio

An efficient iterative solution method for the Chebyshev collocation of advection-dominated transport problems

A new Chebyshev collocation algorithm is proposed for the iterative solution of advection-diffusion problems. The main features of the method lie in the original way in which a finite-difference preconditioner is built and in the fact that the solution is collocated on a set of nodes matching the standard Gauss-Lobatto-Chebyshev set only in the case of pure diffusion problems. The key point of the algorithm is the capability of the preconditioner to represent the high-frequency modes when dealing with advection-dominated problems. The basic idea is developed for a one-dimensional case and is extended to two-dimensional problems. A series of numerical experiments is carried out to demonstrate the efficiency of the algorithm. The proposed algorithm can also be used in the context of the incompressible Navier-Stokes equations

When does crowdsourcing benefit firm stock market performance?

Crowdsourcing is a particular form of open innovation (OI) that aims to boost idea-generation in innovation processes. The underlying rationale is that the collective intelligence of a large number of contributors outside the firm’s boundaries increases the likelihood of achieving ‘extreme outcomes’, i.e., high quality ideas with exceptional business potential. Due to the idiosyncrasies that differentiate crowdsourcing from other forms of OI, the findings from prior research on the performance implications of OI cannot be directly extended to crowdsourcing. Similarly, the findings on the effect of internal R&D on firm performance cannot be directly applied to crowdsourcing due to the greater uncertainty in dealing with a crowd of unknown individuals outside the organization whose ideas have to be evaluated and ultimately processed internally. Thus, while crowdsourcing research has recently burgeoned, it is ambiguous as to whether and when crowdsourcing is beneficial for firms. In fact, the overall effect of crowdsourcing on a firm’s future profits has not been thoroughly investigated. To fill this gap, we conducted an event study analyzing stock market reactions to crowdsourcing announcements, a forward-looking market-based measure able to isolate the effect of crowdsourcing on a firm’s future profits, which we refer to as firm stock market performance. Drawing on the resource-based view, we argue that an external crowd can become a valuable resource if the firm is able to extract value from it. Our findings show that two key contingency factors, i.e., brand value and investment opportunities, determine the boundary conditions that enable firms to extract value from the crowd, resulting in a positive stock market reaction to the announcement of a crowdsourcing campaign. In addition to advancing scholarly knowledge on crowdsourcing, our results provide practitioners with relevant indications for profitable crowdsourcing campaigns