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We demonstrate that gravity acting alone at large length scales (compared to the capillary length) can produce a jet from a sufficiently steep, axisymmetric surface deformation imposed on a quiescent, deep pool of liquid. Mechanistically, the jet owes it origin to the focusing of a concentric, surface wave towards the axis of symmetry, quite analogous to such focusing of capillary waves and resultant jet formation observed during bubble collapse at small scales. A weakly nonlinear theory based on the method of multiple scales in the potential flow limit is presented for a modal (single-mode) initial condition representing the solution to the primary Cauchy–Poisson problem. A pair of novel, coupled, amplitude equations are derived governing the modulation of the primary mode. For moderate values of the perturbation parameter $\epsilon$ (a measure of the initial perturbation steepness), our second-order theory captures the overshoot (incipient jet) at the axis of symmetry quite well, demonstrating good agreement with numerical simulation of the incompressible, Euler equation with gravity (Popinet 2014, Basilisk. http://basilisk.fr) and no surface tension. We demonstrate that the underlying wave focusing mechanism may be understood in terms of radially inward motion of nodal points of a linearised, axisymmetric, standing wave. This explanation rationalises the ubiquitous observation of such jets accompanying cavity collapse phenomena, spanning length scales from microns to several metres. Expectedly, our theory becomes inaccurate as $\epsilon$ approaches unity. In this strongly nonlinear regime, slender jets form with surface accelerations exceeding gravity by more than an order of magnitude. In this inertial regime, we compare the jets in our simulations with the inertial, self-similar, analytical solution by Longuet-Higgins (J. Fluid Mech., 1983, vol. 127, pp. 103–121) and find qualitative agreement with the same. This analysis demonstrates, from first principles, an example of a jet created purely under gravity from a smooth initial perturbation and provides support to the analytical model of Longuet-Higgins (J. Fluid Mech., 1983, vol. 127, pp. 103–121).
In this study, the effects of antagonistic muscle actuation on the propulsion of a bilaminar-structure fish fin ray were investigated using a two-dimensional computational flow–structure interaction (FSI) model. The structure and material properties of the model were based on the realistic biological data of the sunfish fin. The effect of muscle actuation was modelled using root displacement offset between the two hemitrichs. Parametric FSI simulations were conducted by assuming a sinusoidal function of the offset over a cycle and varying the amplitude and phase difference between the actuations and pitching/plunging motions. The results show that the phase of muscle actuation is a critical factor affecting its effects. Three performance regions can be identified with different phase ranges, including a thrust-favour region, an efficiency-favour region and a thrust-efficiency-unfavour region. In each region, the relationships among the root actuations, fin-ray kinematics, vortex dynamics and resulting performance are studied and discussed. Furthermore, a strong positive correlation between the trailing–leading amplitude ratio and thrust coefficient as well as a negative relationship between the efficiency and angle of attack at the centre of mass of the fin ray are observed.
We investigate the effects of fluid elasticity on the flow forces and the wake structure when a rigid cylinder is placed in a viscoelastic flow and is forced to oscillate sinusoidally in the transverse direction. We consider a two-dimensional, uniform, incompressible flow of viscoelastic fluid at $Re=100$, and use the FENE-P model to represent the viscoelastic fluid. We study how the flow forces and the wake patterns change as the amplitude of oscillations, $A^*$, the frequency of oscillations (inversely proportional to a reduced velocity, $U^*$), the Weissenberg number, $Wi$, the square of maximum polymer extensibility, $L^2$, and the viscosity ratio, $\beta$, change individually. We calculate the lift coefficient in phase with cylinder velocity to determine the range of different system parameters where self-excited oscillations might occur if the cylinder is allowed to oscillate freely. We also study the effect of fluid elasticity on the added mass coefficient as these parameters change. The maximum elastic stress of the fluid occurs in between the vortices that are observed in the wake. We observe a new mode of shedding in the wake of the cylinder: in addition to the primary vortices that are also observed in the Newtonian flows, secondary vortices that are caused entirely by the viscoelasticity of the fluid are observed in between the primary vortices. We also show that, for a constant $Wi$, the strength of the polymeric stresses increases with increasing reduced velocity or with decreasing amplitude of oscillations.
The well-known Erdős-Hajnal conjecture states that for any graph $F$, there exists $\epsilon \gt 0$ such that every $n$-vertex graph $G$ that contains no induced copy of $F$ has a homogeneous set of size at least $n^{\epsilon }$. We consider a variant of the Erdős-Hajnal problem for hypergraphs where we forbid a family of hypergraphs described by their orders and sizes. For graphs, we observe that if we forbid induced subgraphs on $m$ vertices and $f$ edges for any positive $m$ and $0\leq f \leq \binom{m}{2}$, then we obtain large homogeneous sets. For triple systems, in the first nontrivial case $m=4$, for every $S \subseteq \{0,1,2,3,4\}$, we give bounds on the minimum size of a homogeneous set in a triple system where the number of edges spanned by every four vertices is not in $S$. In most cases the bounds are essentially tight. We also determine, for all $S$, whether the growth rate is polynomial or polylogarithmic. Some open problems remain.
The phylum Acanthocephala is an important group of parasites with more than 1,300 species parasitizing intestine of all major vertebrate groups. However, our present knowledge of the mitochondrial genomes of Acanthocephala remains very limited. In the present study, we sequenced and annotated the complete mitochondrial genome of Acanthogyrus (Acanthosentis) bilaspurensis (Gyracanthocephala: Quadrigyridae) for the first time based on the specimens recovered from the intestine of common carp Cyprinus carpio Linnaeus (Cyprinidae) in Pakistan. The mitochondrial genome of A. bilaspurensis is 13,360 bp in size and contains 36 genes, representing the smallest mitogenome of acanthocephalans reported so far. The mitogenome of A. bilaspurensis also has the lowest level of overall A+T contents (59.3%) in the mitogenomes of Eoacanthocephala, and the non-coding region 3 (NCR3) lies between trnS2 and trnI, which is different from all of the other acanthocephalan species. Phylogenetic analyses based on concatenating the amino acid sequences of 12 protein-coding genes using maximum likelihood (ML) and Bayesian inference (BI) methods revealed that the family Pseudoacanthocephalidae is a sister to the Arhythmacanthidae rather than the Cavisomatidae, and the families Rhadinorhynchidae and Cavisomatidae showed sister relationships.
Insights gained from modal analysis are invoked for predictive large-eddy simulation (LES) wall modelling. Specifically, we augment the law of the wall (LoW) by an additional mode based on a one-dimensional proper orthogonal decomposition (POD) applied to a two-dimensional turbulent channel. The constructed wall model contains two modes, i.e. the LoW-based mode and the POD-based mode, and the model matches with the LES at two, instead of one, off-wall locations. To show that the proposed model captures non-equilibrium effects, we perform a priori and a posteriori tests in the context of both equilibrium and non-equilibrium flows. The a priori tests show that the proposed wall model captures extreme wall-shear stress events better than the equilibrium wall model. The model also captures non-equilibrium effects due to adverse pressure gradients. The a posteriori tests show that the wall model captures the rapid decrease and the initial decrease of the streamwise wall-shear stress in channels subjected to suddenly imposed adverse and transverse pressure gradients, respectively, both of which are missed by currently available wall models. These results show promise in applying modal analysis for turbulence wall modelling. In particular, the results show that employing multiple modes helps in the modelling of non-equilibrium flows.
This paper offers a unified explanation for the procreation asymmetry and the non-identity thesis – two of the most intractable puzzles in population ethics. According to the procreation asymmetry, there are moral reasons not to create lives that are not worth living but no moral reasons to create lives that are worth living. I explain the procreation asymmetry by arguing that there are moral reasons to prevent the bad, but no moral reasons to promote the good. Various explanations for the procreation asymmetry have failed to explain the non-identity thesis: if one could create a person with a good life or a different person with a better life, one has a moral reason to create the better life. I argue that reflections on the misfortune of unfulfilled potential allow us to circumvent the non-identity problem.
En este trabajo se discute un conjunto de indicios de poblamiento humano en diferentes locus de la Pampa Occidental: el sitio 1 de la localidad Tapera Moreira, El Carmel y Casa de Piedra. El poblamiento inicial de este territorio ha estado restringido a un solo dato cronológico correspondiente al Holoceno temprano, proveniente del sitio Casa de Piedra 1 (8620 ± 190 años aP) que no ha sido replicado en ese u otros sitios de la región. Por ello no ha sido incorporado en la agenda de la discusión sobre esta temática en publicaciones recientes. Sin embargo, en años posteriores a su publicación se han suscitado diversos hallazgos cuyos contextos señalan gran potencial informativo en relación con la ocupación humana inicial de paisajes sin historia previa. Se presentan indicadores de cultura material (puntas de tipo cola de pescado, litos discoidales y materias primas muy seleccionadas y con tratamiento térmico) recuperados en asociación en diferentes locus pampeanos, que se relacionan con las expectativas generadas para una etapa de ocupación inicial del paisaje. Se propone un modelo de exploración lenta y discontinua que utilizó vías de transitabilidad de distinto rango en el proceso de conocimiento y colonización de estos ambientes desérticos.
Through computational-assisted analysis of the Weibo corpus of the Chinese Communist Youth League (CYL) spanning from 2013 to 2020, this paper unveils the strategic utilization of fandom culture by the CYL, the youth wing of the ruling party, in its nationalistic propaganda on the internet. Specifically, the CYL deliberately associates with the pop idols of the younger generation on Weibo, harnessing their influence to promote nationalistic content that encompasses both “pride-oriented” and “hostility-oriented” themes. Subsequent analysis reveals a greater propensity for nationalistic content to generate audience response compared to other types of content, particularly when endorsed by these pop idols. This research enriches our understanding of the CYL's propaganda efforts and contributes to the burgeoning scholarship on “soft propaganda” in China.
Epistemic uncertainties are included in probabilistic risk assessment (PRA) as second-order probabilities that represent the degrees of belief of the scientists that a model is correct. In this article, I propose an alternative approach that incorporates the scientist’s confidence in a probability set for a given quantity. First, I give some arguments against the use of precise probabilities to estimate scientific uncertainty in risk analysis. I then extend the “confidence approach” developed by Brian Hill and Richard Bradley to PRA. Finally, I claim that this approach represents model uncertainty better than the standard (Bayesian) model does.
Trip-resolved large-eddy simulations of the DARPA SUBOFF are performed to investigate the development of turbulent boundary layers (TBLs) in model-scale studies. The primary consideration of the study is the extent to which the details of tripping affect statistics in large-eddy simulations of complex geometries, which are presently limited to moderate Reynolds number TBLs. Two trip wire configurations are considered, along with a simple numerical trip (wall-normal blowing), which serves as an exemplar of artificial computational tripping methods often used in practice. When the trip wire height exceeds the laminar boundary layer thickness, shedding from the trip wire initiates transition, and the near field is characterized by an elevation of the wall-normal Reynolds stress and a modification of the turbulence anisotropy and mean momentum balance. This trip wire also induces a large jump in the boundary layer thickness, which affects the way in which the TBL responds to the pressure gradients and streamwise curvature of the hull. The trip-induced turbulence decays along the edge of the TBL as a wake component that sits on top of the underlying TBL structure, which dictates the evolution of the momentum and displacement thicknesses. In contrast, for a trip wire height shorter than the laminar boundary layer thickness, transition is initiated at the reattachment point of the trip-induced recirculation bubble, and the artificial trip reasonably replicates the resolved trip wire behaviour relatively shortly downstream of the trip location. For each case, the inner layer collapses rapidly in terms of the mean profile, Reynolds stresses and mean momentum balance, which is followed by the collapse of the Reynolds stresses in coordinates normalized by the local momentum thickness, and finally against the 99 % thickness. By this point, the lasting impact of the trip is the offset in boundary layer thickness due to the trip itself, which becomes a diminishing fraction of the total boundary layer thickness as the TBL grows. The importance of tripping the model appendages is also highlighted due to their lower Reynolds numbers and susceptibility to laminar separations.
Epidemiological studies on the potential health effects of dietary polyamines are scarce. The present study aimed to estimate habitual intake of polyamines (putrescine, spermidine and spermine) and examine whether spermidine intake is inversely associated with all-cause and cause-specific mortality in a population-based cohort study in Japan. The study included 13 355 men and 15 724 women aged 35 years and older. Diet was assessed via a validated FFQ at the baseline in 1992. The intake of polyamines was estimated mainly using databases of polyamine content in foods consumed among Japanese population. Sex-specific hazard ratios (HR) and 95 % CI for all-cause and cause-specific mortality were estimated according to polyamine quartiles. During 16 years of follow-up, 2901 deaths in men and 2438 in women occurred. The intake of any polyamine was not significantly associated with all-cause or cause-specific mortality after controlling for covariates in men and women. There was a suggestive positive association between spermidine intake and cancer mortality in women: HR for the highest v. lowest quartile were 1·38 (95 % CI (0·99, 1·93); Ptrend = 0·02). Our results did not provide support for the notion that dietary spermidine has beneficial effects on mortality. Further studies on dietary polyamines and longevity, as well as the morbidity of specific diseases, including cancer, are needed across populations with different dietary habits.
Hegel's Science of Logic is one of the most challenging books in the philosophical library. Its primary text is a mass of abstract terms, woven into sentences that become quite complex. That text avoids illustrations or examples, but plunges on from paragraph to paragraph as the concepts being discussed subtly change their character, develop associations with contrary terms, become part of a complex network of reciprocal interaction, and then collapse into a new integrated thought which then serves as an immediate beginning for the next discussion.
This article aims to reexamine the relationship between the artist Lee Ufan and nationalist art history through his idea of “ambivalent otherness,” which he defined as both “suffering” and “power.” Traditional art history is established upon a nationalist framework that emphasizes the artists' nationality, leading to the marginalization of national others at the border. As a zainichi Korean, Lee has undergone the “suffering” of being excluded by the art world and art historiography. However, he transformed it into his source of “power” to challenge art historiography based on nationality. This study analyzes the art criticism of “Japanese Contemporary Art History” written by Minemura Toshiaki and Chiba Shigeo in the 1970s and 1980s and highlights the ruptures that the artist's in-between identity wrought on nationalist art history. This shows how both the Mono-ha movement and the artist were marginalized in the construction of “Japanese Contemporary Art History.” Furthermore, this study scrutinizes how Lee attempted to rewrite art history using Mono-ha art theory and a perspective committed to “overcoming coloniality” from the postcolonial in-between position, by reinterpreting Lee's article on Chosŏn minhwa, written amidst an aesthetic controversy across the border between Japan and Korea.
Este trabajo se propone avanzar en la comprensión de los procesos históricos de pintado del sitio arqueológico de Oyola (Sierra El Alto-Ancasti, Catamarca, Argentina). En particular, se evalúan similitudes y diferencias en la composición material de las mezclas pigmentarias para entrever la existencia de antiguas recetas pictóricas en la confección de las pinturas rupestres negras. Para ello se realizaron análisis microestratigráficos de 28 motivos mediante microscopía electrónica de barrido con análisis elemental por espectroscopía dispersiva en energía de rayos X (MEB-EDS), y microespectroscopía Raman (RS). Su estudio comparativo señaló el uso alternativo de dos pigmentos negros (carbón vegetal y óxidos de manganeso) combinados, en algunos casos, con un aditivo (sulfato de calcio). De esta forma, fue posible conocer ciertos aspectos de las recetas pictóricas que orientaron la preparación de las mezclas pigmentarias negras, aproximándonos a algunas de las tradiciones y saberes retomados. Para alcanzar una comprensión histórica de dichas recetas, se evaluó la distribución espacial, temporal y algunas características formales de los motivos rupestres realizados con ellas. Al no identificarse tendencias claras, se propone una definición menos normativa de receta pictórica que resalta los aspectos compartidos entre distintos episodios de pintado sin perder de vista las posibilidades creativas de cada evento.