Miracle-dz/UniFAR-FTUs huggingface dataset:
Compressor Leading Edge Spikes: A New Performance Criterion

Compressor blades often have a small "spike" in the surface pressure distribution at the leading edge. This may result from blade erosion, manufacture defects, or compromises made in the original design process. This paper investigates the effect of these spikes on profile loss, and presents a criterion to ensure they are not detrimental to compressor performance. In the first part of the paper, two geometries of leading edge are tested. One has a small spike, typical of those found on modern compressors; the other has no spike, characteristic of an idealized leading edge. Testing was undertaken on the stator of a single-stage low speed compressor. The time resolved boundary layer was measured using a hot-wire microtraversing system. It is shown that the presence of the small spike changes the time resolved transition process on the suction surface, but that this results in no net increase in loss. In the second part of the paper, spike height is systematically changed using a range of leading edge geometries. It is shown that below a critical spike height, the profile loss is constant. If the critical spike height is exceeded, the leading edge separates and profile loss rises by 30%. Finally, a criterion is developed, based on the total diffusion across the spike. Three different leading edge design philosophies are investigated. It is shown that if the spike diffusion factor is kept below 0.1 over the blade's incidence range, performance is unaffected by leading edge geometry.
On gravity currents in a linearly stratified ambient: a generalization of Benjamin's steady-state propagation results

This paper presents a generalization of the classical results of T. B. Benjamin (J. Fluid. Mech. vol. 31, 1968, p. 209) concerning the propagation of a steady gravity current into a homogeneous ambient, to the case of a stratified ambient. The current of thickness $h$ and density $\roh_c$ propagates, with speed $U$, at the bottom of a long horizontal channel of height $H$, into the unperturbed ambient whose density increases linearly from $\roh_o$ (at the top) to $\roh_b$ (at the bottom). The reduced gravity is $g^{\prime} \,{=}\, (\roh_c/\roh_o -1)g$ and the governing parameters are $a \,{=}\, h/H$ and $S \,{=}\, (\roh_b-\roh_o)/(\roh_c-\roh_o)$, with $0<a<1, 0 < S < 1 $; here $g$ is the acceleration due to gravity. For a Boussinesq high-Reynolds two-dimensional configuration, a flow-field solution of Long's model, combined with flow-force balance over the width of the channel, are used for obtaining the desired results, in particular: $\hbox{\it Fr} \,{=}\, U/(g^{\prime}h)^{1/2}$, head loss (dissipation), and criticality of $U$ with respect to the fastest internal wave mode. The classical results of Benjamin are fully recovered for $S \rightarrow 0$. For small $S$ and fixed $a$, the values of $\hbox{\it Fr}$ and head loss are shown to decrease with $S$ like $(1-2S/3)^{1/2}$ and $(1-2S/3)$, respectively, and the propagation is supercritical. For larger $S$ several solutions are possible (for a given geometry $a$), mostly in the subcritical regime. Considerations for the physical acceptability of the multiple results are presented, and the connection with observations from lock-release experiments are discussed. The conclusion is that the present results provide a reliable and versatile generalization of the classical unstratified problem.
A numerical study of the unstratified and stratified Ekman layer

Abstract We study the turbulent Ekman layer at moderately high Reynolds number, $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}1600 < \mathit{Re} = \delta _{E}G/\nu < 3000$ , using direct numerical simulations (DNS). Here, $\delta _{E} = \sqrt{2\nu /f}$ is the laminar Ekman layer thickness, $G$ the geostrophic wind, $\nu $ the kinematic viscosity and $f$ is the Coriolis parameter. We present results for both neutrally, moderately and strongly stably stratified conditions. For unstratified cases, large-scale roll-like structures extending from the outer region down to the wall are observed. These structures have a clear dominant frequency and could be related to periodic oscillations or instabilities developing near the low-level jet. We discuss the effect of stratification and $\mathit{Re}$ on one-point and two-point statistics. In the strongly stratified Ekman layer we observe stable co-existing large-scale laminar and turbulent patches appearing in the form of inclined bands, similar to other wall-bounded flows. For weaker stratification, continuously sustained turbulence strongly affected by buoyancy is produced. We discuss the scaling of turbulent length scales, height of the Ekman layer, friction velocity, veering angle at the wall and heat flux. The boundary-layer thickness, the friction velocity and the veering angle depend on $Lf/u_\tau $ , where $u_\tau $ is the friction velocity and $L$ the Obukhov length scale, whereas the heat fluxes appear to scale with $L^+=L u_\tau /\nu $ .
Tube theory of entangled polymer dynamics

The dynamics of entangled flexible polymers is dominated by physics general to many chemical systems. It is an appealing interdisciplinary field where experimental and theoretical physics can work closely with chemistry and chemical engineering. The role of topological interactions is particularly important, and has given rise to a successful theoretical framework: the 'tube model'. Progress over the last 30 years is reviewed in the light of specially-synthesized model materials, an increasing palette of experimental techniques, simulation and both linear and nonlinear rheological response. Our current understanding of a series of processes in entangled dynamics: 'reptation', 'contour length fluctuation' and 'constraint-release' are set in the context of remaining serious challenges. Especial attention is paid to the phenomena associated with polymers of complex topology or 'long chain branching'.
CFD simulations and particle image velocimetry measurements in an industrial scale rotating disc contactor

Fluid dynamics of the single-phase and two-phase flow in a segment of a rotating disc contactor (RDC) liquid–liquid extraction column with 450 mm inner diameter were studied by performing computational fluid dynamics (CFD) simulations and particle image velocimetry (PIV) measurements. The fluid dynamics were investigated to test the predictivity of CFD at industrial scale. Different turbulence models in conjunction with the Eulerian approach were applied in the single-phase and two-phase simulations. The turbulent flow characteristics were analyzed by PIV measurements to validate the CFD simulations. An iso-optical system composed of CaCl2/water–butylacetate allows for the two-phase PIV measurements. Local turbulent energy dissipation was derived from velocity gradients in PIV data. In this connection, the influence of the PIV spatial resolution on the measured energy dissipation was also analyzed, and different fit functions were tested to scale the measured energy dissipation. Simulated velocity fields as well as the energy dissipation were compared with the experimental PIV data. The results from the simulations and experiments are in good agreement. The work shows that CFD can predict hydrodynamic characteristics even at bigger scales but is still subject to some minor restrictions. © 2010 American Institute of Chemical Engineers AIChE J, 2011
A note on potential energy density in a stratified compressible fluid

An exact, local, positive definite expression is obtained for the potential energy density in a wide class of stratified compressible fluids. This expression is an extension of that derived for incompressible stratified fluids in the preceding paper by Holliday & McIntyre (1981), and also represents a finite-amplitude analogue of the disturbance potential energy density that is familiar in small-amplitude theory. Its volume integral reduces to Lorenz’ (1955) available potential energy under suitable choice of a hydrostatic reference state, provided that the fluid is contained within a fixed volume enclosed by rigid impermeable boundaries.
The Formation of Stellar Galactic Nuclei through Dissipative Gas Dynamics

Abstract It is a long-standing and remarkable problem as to howstellar galactic nuclei (SGN) were formed in the central region of galaxies. In order to elucidate the formation processes of SGN, we numerically investigate gas dynamics, star formation, and chemical evolution in the central 1–1000 pc of gas disks embedded by galactic stellar spheroids. The main results of the present numerical study are: (a) SGN can be formed from dissipative, repeated merging of massive stellar and gaseous clumps that have typical masses of 105–106 M⊙ and are developed from nuclear gaseous spiral arms owing to local gravitational instability. Typically ∼5% of the masses of their host spheroids can be transfered to the central∼50 pc and thus become SGN. (b) SGN have very flattened shapes, and rotational kinematics and central velocity dispersions much smaller than those of their host spheroids. These structural and kinematic characteristics do not depend on model parameters such as masses of spheroids (M sph) and initial gas mass fraction (f g). (c) Stellar populations of SGN can show a wide rage of ages and metallicities, because SGN are formed from massive clumps with different star-formation and chemical-evolution histories. The mean metallicities of SGN can be significantly higher than those of their host spheroids. (d) More massive, higher density SGN can be formed in spheroids with higher surface brightness. Furthermore there can be a threshold value (∼0.2) of f g below which massive SGN are less likely to be formed in the central gas disks of spheroids. (e) More massive spheroids can have more massive, more metal-rich and higher-density SGN, because star formation and chemical enrichment proceed more efficiently owing to the less dramatic suppression of star formation by supernovae feedback effects in more massive spheroids. Based on these results, we discuss correlations between the physical properties of SGN and those of their host galaxies, structural and kinematic properties of SGN of dwarf elliptical galaxies and the origin of very massive star clusters such as ω Cen and ultra-compact dwarf galaxies.
NUMERICAL COMPUTATIONS AND VISUALIZATION TESTS OF THE FLOW INSIDE A COLD GAS SIMULATION WITH CHARACTERIZATION OF A PARIETAL VORTEX SHEDDING

&The flow inside the channel of a cold gas set-up, generated by an injection at the wall, in which a parietal vortex shedding occurs in consequence of the development of its natural instabilities, has been computed and visualized. Computations have been performed with a 2D numerical code on a very refined mesh as to capture the flow instabilities. The oscillatory characteristics of the flow found for two injection velocities are in good agreement with those determined from experiments. Moreover, parietal vortex sheddings, taking place into the downstream part of the channel from an abscissa normalized by the channel of 20, are characterized. The flow has been visualized by means of a PLDF technique applied on gaseous acetone injected at the upstream part of the injecting wall. Vortices convected by the flow are well identified on the pictures from the abscissa determined from the computations.
ASYMPTOTICS FOR THE LOW‐FREQUENCY ORDINATES OF THE PERIODOGRAM OF A LONG‐MEMORY TIME SERIES

We consider the asymptotic distribution of the normalized periodogram ordinates I(ωj)/f(ωj) (j= 1,2,…) of a general long-memory time series. Here, I(ω;) is the periodogram based on a sample size n, f(ω) is the spectral density and ωj= 2πj/n. We assume that n∝ with j held fixed, and so our focus is on low frequencies; these are the most important frequencies for the periodogram-based estimation of the memory parameter d. Contrary to popular belief, the normalized periodogram ordinates obtained from a Gaussian process are asymptotically neither independent identically distributed nor exponentially distributed. In fact, limn E{I(ωj)/f(ωj)} depends on both j and d and is typically greater than unity, implying a positive asymptotic relative bias in I(ωj) as an estimator of f(ωj). Tapering is found to reduce this bias dramatically, except at frequency ω1. The asymptotic distribution of I(ωj)/f(ωj) for a Gaussian process is, in general, that of an unequally weighted linear combination of two independent X21 random variables. The asymptotic mean of the log normalized periodogram depends on j and d and is not in general equal to the negative of Euler's constant, as is commonly assumed. Consequently, the regression estimator of d proposed by Geweke and Porter-Hudak will be asymptotically biased if the number of frequencies used in the regression is held fixed as n∝.
Y OPHIUCHI REVISITED

New Stroemgren by photometry of the 17d Cepheid, Y Oph, is presented as a contribution to understanding its period change. A rediscussion of all available data leads to the conclusion that this period change is smooth rather than discontinuous and is consistent with theoretical expectations. An investigation of the V light curve over the past hundred years suggests that its amplitude at the turn of the century may have been about 0.7 mag as against its present value of 0.5 mag. If so, Y Oph would be the second Cepheid after Polaris to show such a secular decline. Neither Y Oph nor Polaris (which also has an increasing period) lie close to the red edge of the instability strip, so any suggestion that they are about to evolve out of the strip seems premature.
Archetypes of sourcing decision­making: the influence of contextual factors on consensus, argumentation and cabal

Purpose – This article develops a taxonomy of sourcing decision-making (SDM) archetypes and explores how different contextual factors influence these archetypes when global sourcing of complex components is considered a viable option. Design/methodology/approach – A multiple case study approach with five in-depth cases is employed. In total, 19 interviews as well as publicly available and internal data from large buying firms headquartered in Austria and Germany were collected and analyzed. Findings – The results reveal three different SDM archetypes which are described in detail (i.e., ‘consensus’, ‘argumentation’ and ‘cabal’). Furthermore, it is found that these archetypes are mainly influenced by three contextual factors: sourcing maturity, product complexity and leadership style. The final model comprises six propositions which illustrate how these contextual factors determine companies’ SDM archetypes. Research limitations/implications – The study contributes to theory development at the intersection of organizational buying behavior and the (global) sourcing decision-making literature. Thereby, it answers the call for more rigorous investigation of the influence of contextual factors on SDM processes. Practical implications – The findings enable practitioners to better understand and consequently manage SDM processes and their outcomes. By supporting decision-makers in identifying SDM archetypes, this study allows sourcing managers and teams to make better decisions by avoiding problems that occur in situations in which the preferred decision-making type would result in suboptimal decisions. Originality/value – The study provides a first step towards a taxonomy of SDM archetypes and is among the first that explores their underlying contextual factors.
Nanoscale Spatial Distribution of Tethered DNA on Model Nucleic Acid Sensor Surfaces

: The nanoscale arrangement of the DNA probe molecules on sensor surfaces has a profound impact on molecular recognition and signaling reactions on DNA biosensors and microarrays. Using electrochemical atomic force microscopy, we have directly determined the nanoscale spatial distribution of thiolated DNA that are attached to gold via different methods. We discovered significant heterogeneity in the probe density and limited stability for DNA monolayers prepared by the backfilling method, that is, first exposing the surface to thiolated DNA then “backfilling” with a passivating alkanethiol. On the other hand, the monolayers prepared by “inserting” thiolated DNA into a preformed alkanethiol monolayer lead to a more uniformly distributed layer of DNA. With high-resolution images of single DNA molecules on the surface, we have introduced spatial statistics to characterize the nanoscale arrangement of DNA probes. The randomness of the spatial distribution has been characterized. By determining the local densities surrounding individual molecules, we observed subpopulations of probes with dramatically different levels of “probe crowding”. We anticipate that the novel application of spatial statistics to DNA monolayers can enable a framework to understand heterogeneity in probe spatial distributions, interprobe interactions, and ultimately probe activity on sensor surfaces.
Ion distribution in ionic electroactive polymer actuators

Ionic electroactive polymer (i-EAP) actuators with large strain and low operation voltage are extremely attractive for applications such as MEMS and smart materials and systems. In-depth understanding of the ion transport and storage under electrical stimulus is crucial for optimizing the actuator performance. In this study, we show the dominances of ion diffusion charge and we perform direct measurements of the steady state ion distribution in charged and frozen actuators by using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). High temperature actuators that consist Aquivion ionomer membrane and high melting temperature ionic liquid 1-butyl-2,3-dimethylimidazolium chloride (BMMI-Cl]) served in this study. Electrical impedance, I-V characteristics, and potential step charging of the actuator are characterized at 25°C and 100°C. The conductivity of the actuator is 0.3mS/cm at 100°C and 2. 9μS/cm at 25°C, respectively. The electrochemical window of the device is 3V and a 2mm tip displacement is observed under 2.5V 0.2Hz at 100°C. A semi-quantitative depth profile of the relative ion concentration in charged and frozen actuators is measured by ToF-SIMS. The result shows that, unlike semiconductors, ions do not deplete from the electrodes with same signs. Due to a strong cluster effect between the ions, Cl- and BMMI+ accumulate near both cathode and anode. Furthermore, the profile indicates that the ion size difference causes the BMMI+ space charge layers (~6um) much thicker than those of Cl- (~0.5um).
The presence of large sunspots near the central solar meridian at the times of major geomagnetic storms

Abstract. A further study is made of the validity of a technique developed by the authors to identify historical occurrences of intense geomagnetic storms, which is based on finding approximately coincident observations of sunspots and aurorae recorded in East Asian histories. Previously, the validity of this technique was corroborated using scientific observations of aurorae in Japan during the interval 1957–2004 and contemporaneous white-light images of the Sun obtained by the Royal Greenwich Observatory, the Big Bear Solar Observatory, the Debrecen Heliophysical Observatory, and the Solar and Heliospheric Observatory spacecraft. The present investigation utilises a list of major geomagnetic storms in the interval 1868–2008, which is based on the magnitude of the AA* magnetic index, and reconstructed solar images based on the sunspot observations acquired by the Royal Greenwich Observatory during the shorter interval 1874–1976. It is found that a sunspot large enough to be seen with the unaided eye by an "experienced" observer was located reasonably close to the central solar meridian for almost 90% of these major geomagnetic storms. Even an "average" observer would easily achieve a corresponding success rate of 70% and this success rate increases to about 80% if a minority of ambiguous situations are interpreted favourably. The use of information on major geomagnetic storms, rather than modern auroral observations from Japan, provides a less direct corroboration of the technique for identifying historical occurrences of intense geomagnetic storms, if only because major geomagnetic storms do not necessarily produce auroral displays over East Asia. Nevertheless, the present study provides further corroboration of the validity of the original technique for identifying intense geomagnetic storms. This additional corroboration of the original technique is important because early unaided-eye observations of sunspots and aurorae provide the only possible means of identifying individual geomagnetic storms during the greater part of the past two millennia.
com-Seasonal changes of bird assemblages in a small urban wetland revealed by mist-netting Sezónne zmeny vtáčích spoločenstiev malej mokrade v mestskom prostredí: analýza odchytov

: Seasonal differences of bird assemblages were studied using mist-netting method during four seasons (May, July, September, and December) in two years (2014 and 2021) in a secondary wetland habitat (7 mist-nets in willow grove, reed, and scrubland) in Zvolen town, central Slovakia. Altogether 54 species and 876 individuals of birds were captured during 24 days of eight trapping sessions (in 84 m of mist-nets at 7.3 ha study plot). The highest number of mist-netted species and individuals was found in July (36 species, 290 individuals), the lowest was in December (16 species, 153 individuals), pooled for both years. The most abundant species were breeding species Sylvia atricapilla, Parus major, Cyanistes caeruleu s and Turdus merula . The characteristic reedbed birds included four Acrocephalus species , Locustella luscinioides, Emberiza schoeniclus , and scrubland species Luscinia megarhynchos, Sylvia communis and Remiz pendulinus . Seasonal differences in species number and abundance are discussed. Regular wintering was found in migratory species Prunella modularis and Erithacus rubecula north of the known winter quarters of their central European breeding populations. The site fidelity and between-season retraps were confirmed in 10 species and 54 individuals (18.5% of all mist-netted species and 6.2% of all individuals). Based on retrapped individuals, the resident species P. major, C. caeruleus, Aegithalos caudatus and T. merula were the most faithful to the site, whereas inter-seasonal retraps of migratory species were rare (e. g. Sylvia atricapilla, Luscinia megarhynchos and Phylloscopus collybita ).
The life cycle of convective‐shower cells under post‐frontal conditions

Seventeen days with post‐frontal shower precipitation are analysed by means of radar data obtained from the German Weather Service's C‐band radar network. The life cycle of clusters—defined here as contiguous rain areas including one or more radar‐reflectivity peaks (i.e. convection cells)—is investigated. To allow for the continuous tracking of clusters, sometimes over a time period of more than an hour, a new, specially adapted tracking algorithm has been developed. The life cycle of convective clusters comprises five different stages: genesis; growth (including merging); stagnation; decay (including splitting); and dissolving. The transition likelihoods from a cluster with n maxima to one with m maxima are determined (the case m > n corresponding to growth and m < n to decay). It is found that, predominantly, clusters grow or decay by one cell. Results relating to the temporal evolution of post‐frontal showers are presented, and a conceptual growth model is proposed. Although single cells are the most frequent cluster type, the spatial structure of the post‐frontal precipitation field is dominated by multi‐celled clusters. Their life cycle is essentially affected by cell merging and splitting. Although the transitions of all (about one million) identified clusters have been analysed and quantified, more research is necessary in order to understand the underlying principles of cluster growth. Copyright © 2008 Royal Meteorological Society