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where $f: X \to {\Bbb R}$, X a set, finite or infinite, and K and $\mu $ denote a suitable kernel and a measure, respectively. Given a connected ordered graph G on n vertices, consider the multi-linear form
holds for all nonnegative real-valued functions $f_i$, $1\le i\le n$, on X. The basic question is, how does the structure of G and the mapping properties of the operator $T_K$ influence the sharp exponents in (0.1). In this paper, this question is investigated mainly in the case $X={\Bbb F}_q^d$, the d-dimensional vector space over the field with q elements, $K(x^i,x^j)$ is the indicator function of the sphere evaluated at $x^i-x^j$, and connected graphs G with at most four vertices.
Why does an authoritarian regime adopt meritocracy in its political selection? I argue that meritocracy can be used to co-opt large numbers of ordinary citizens by providing them with an opportunity of socioeconomic advancement instead of income redistribution, as long as the selection process is viewed as inclusive and rule-based. Focusing on the civil service examination in contemporary China, I examine how this meritocratic selection has shaped the relationship between college graduates and the Chinese regime. Exploiting a spatial-cohort variation in applicant eligibility, I find that the exam boosts college graduates’ perceived upward mobility, which in turn weakens their demand for redistribution even in the face of growing inequality. These findings point to an alternative mode of authoritarian co-optation and highlight the role of upward mobility in regime stability.
Eukaryotic swimming cells such as spermatozoa, algae or protozoa use flagella or cilia to move in viscous fluids. The motion of their flexible appendages in the surrounding fluid induces propulsive forces that balance viscous drag on the cells and lead to a directed swimming motion. Here, we use our recently built database of cell motility (BOSO-Micro) to investigate the extent to which the shapes of eukaryotic swimming cells may be optimal from a hydrodynamic standpoint. We first examine the morphology of flexible flagella undergoing waving deformation and show that their amplitude-to-wavelength ratio is near that predicted theoretically to optimise the propulsive efficiency of active filaments. Next, we consider ciliates, for which locomotion is induced by the collective beating of short cilia covering their surface. We show that the aspect ratios of ciliates are close to that predicted to minimise the viscous drag of the cell body. Both results strongly suggest a key role played by hydrodynamic constraints, in particular viscous drag, in shaping eukaryotic swimming cells.
Successions in Oklahoma and Nevada record trilobite extinction and replacement near the Steptoean–Sunwaptan boundary in inner-shelf and outer-shelf settings, respectively. Prior to the extinctions, different trilobite biofacies occupied these environments, but faunas became similar in composition across the environmental gradient in the overlying I. “major” and Taenicephalus zones. Faunal changes in the outer shelf at the I. “major” Zone begin at a drowning unconformity that brought dark, laminated calcisiltite and silty lime mudstone above a subtidal carbonate succession. In contrast, Oklahoma shows facies continuity in a succession of tidally influenced bioclastic carbonates. Loss of genera and a dramatic abundance “spike” of Irvingella are features of the I. “major” Zone in both regions. Turnover of biofacies occurred in the succeeding Taenicephalus Zone, with both the inner and outer shelf dominated by Orygmaspis (Parabolinoides). Blooms of orthid brachiopods in shallow water settings are underappreciated signals of faunal change in the extinction interval. Although absent from the outer shelf in Nevada, orthids became abundant enough in Oklahoma to form shell beds in the lower Taenicephalus Zone, but became rare in overlying strata. Carbon isotope stratigraphy includes a modest positive δ13C excursion that peaks in the extinction interval at 1.4‰ (Oklahoma) and 2.2‰ (Nevada), which is congruent with previous reports from Utah and Wyoming. Although consistent with regional upwelling of dysoxic waters, the absence of sedimentary evidence for significant environmental change over much of the shelf is problematic. This suggests that physical environmental change acted primarily as a catalyst for cascading ecological and biogeographic effects.
We prove a conjectural formula for the Brumer–Stark units. Dasgupta and Kakde have shown the formula is correct up to a bounded root of unity. In this paper, we resolve the ambiguity in their result. We also remove an assumption from Dasgupta–Kakde’s result on the formula.
Non-alcoholic fatty liver disease (NAFLD) is a prevalent liver disorder, affecting approximately 25 % of the population. Coffee-drinking obese smokers exhibit lower body weights and decreased NAFLD rates, but the reasons behind this remain unclear. Additionally, the effect of nicotine, the main component of tobacco, on the development of NAFLD is still controversial. Our study aimed to explore the possible reasons that drinking coffee could alleviate NAFLD and gain weight and identify the real role of nicotine in NAFLD of obese smokers. A NAFLD model in mice was induced by administering nicotine and a high-fat diet (HFD). We recorded changes in body weight and daily food intake, measured the weights of the liver and visceral fat, and observed liver and adipose tissue histopathology. Lipid levels, liver function, liver malondialdehyde (MDA), superoxide dismutase (SOD), serum inflammatory cytokine levels and the expression of hepatic genes involved in lipid metabolism were determined. Our results demonstrated that nicotine exacerbated the development of NAFLD and caffeine had a hepatoprotective effect on NAFLD. The administration of caffeine could ameliorate nicotine-plus-HFD-induced NAFLD by reducing lipid accumulation, regulating hepatic lipid metabolism, alleviating oxidative stress, attenuating inflammatory response and restoring hepatic functions. These results might explain why obese smokers with high coffee consumption exhibit the lower incidence rate of NAFLD and tend to be leaner. It is essential to emphasise that the detrimental impact of smoking on health is multifaceted. Smoking cessation remains the sole practical and effective strategy for averting the tobacco-related complications and reducing the risk of mortality.
A data-driven framework using snapshots of an uncontrolled flow is proposed to identify, and subsequently demonstrate, effective control strategies for different objectives in supersonic impinging jets. The open-loop, feed-forward control approach, based on a dynamic mode decomposition reduced-order model (DMD-ROM), computes forcing receptivity in an economical manner by projecting flow and actuator-specific forcing snapshots onto a reduced subspace and then evolving the dynamics forwards in time. Since it effectively determines a linear response around the unsteady flow in the time domain, the method differs materially from typical techniques that use steady basic states, such as stability or input–output approaches that employ linearized Navier–Stokes operators in the frequency domain. The method presented naturally accounts for factors inherent to the snapshot basis, including configuration complexity and flow parameters such as Reynolds number. Furthermore, gain metrics calculated in the reduced subspace facilitate rapid assessments of flow sensitivities to a wide range of forcing parameters, from which optimal actuator inputs may be selected and results confirmed in scale-resolved simulations or experiments. The DMD-ROM approach is demonstrated from two different perspectives. The first concerns asymptotic feedback resonance, where the effects of harmonic pressure forcing are estimated and verified with nonlinear simulations using a blowing–suction actuator. The second examines time-local behaviour within critical feedback events, where the phase of actuation becomes important. For this, a conditional space–time mode is used to identify the optimal forcing phase that minimizes convective instability growth within the resonance cycle.
Canopy flows in the atmospheric surface layer play important economic and ecological roles, governing the dispersion of passive scalars in the environment. The interaction of high-velocity fluid and large-scale surface-mounted obstacles in canopy flows produces drag and causes intense, inhomogeneous and anisotropic turbulence. In this work, we focus on the turbulent dispersion of passive scalars by studying the ‘pair dispersion’ – a statistical measure of relative motion between particles. We analyse the results of a three-dimensional particle tracking velocimetry experiment in a wind-tunnel canopy flow, focusing on small scales. We confirm the existence of local isotropy of pair dispersion at scales smaller than a characteristic shear length scale $L_\varGamma =(\epsilon /\varGamma ^3)^{1/2}$, where $\epsilon$ and $\varGamma$ are the mean dissipation rate and shear rate, respectively. Furthermore, we show that pair dispersion in this locally isotropic regime is a scale-dependent super-diffusive process, similar to what occurs in homogeneous isotropic turbulent flows. In addition, we measure the pair relative velocity correlation function, showing that its de-correlation occurs in the locally isotropic regime, and discuss the implications of this observation for modelling pair dispersion. Thus, our study extends the fundamental understanding of turbulent pair dispersion to the anisotropic inhomogeneous turbulent canopy flow, bringing valuable information for modelling scalar dispersion in the atmospheric surface layer.
The concept of a loess transportation surface portends that saltating sands deflate silt/dust and send them into suspension. This process continues until a topographic barrier stops the saltating sand, allowing loess deposits to accumulate downwind. This paper reports on loess transportation surfaces in west-central Wisconsin, USA. During the postglacial period, cold, dry conditions coincided with strong northwesterly winds to initiate widespread saltation of freely available sands, deflating any preexisting loess deposits. Large parts of the study area are transportation surfaces, and lack loess. Loess deposits were only able to accumulate at “protected” sites—downwind from (east of) topographic barriers, such as isolated bedrock uplands and the north-to-south flowing Black River. Loess in locations from these barriers is thicker (sometimes >5 m) than would be expected, and in places has even accumulated above preexisting loess deposits. For example, downwind (east) of the Black River, most of the low-relief landscape is covered with ≈40–70 cm of silty loess, even though it is many tens of kilometers from the initial loess source. Upwind of the river, on the transportation surface, the low-relief landscape is only intermittently mantled with thin, scattered deposits of silty-sandy eolian sediment, and generally lacks loess.
The impact of fluid drops on solid substrates is a cardinal fluid dynamics phenomenon intrinsically related to many fields. Although these impacting objects are very often non-spherical and non-Newtonian, previous studies have mainly focused on spherical Newtonian drops. As a result, both shape and rheological effects on the drop-spreading dynamics remain largely unexplored. In the present work we use a mixed approach combining experiments with multiphase three-dimensional numerical simulations to extend the work reported by Luu & Forterre (J. Fluid Mech., vol. 632, 2009, pp. 301–327) by highlighting the fundamental role of shape in the normal impact of viscoplastic drops. Such complex fluids are highly common in various industrial domains and ideally behave either like a rigid body or a shear-rate-dependent liquid, according to the stress solicitation. Spherical, prolate, cylindrical and prismatic drops are considered. The results show that, under negligible capillary effects, the impacting kinetic energy of the drop is dissipated through viscoplastic effects during the spreading process, giving rise to three flow regimes: (i) inertio-viscous, (ii) inertio-plastic, and (iii) mixed inertio-visco-plastic. These regimes are deeply affected by the drop initial aspect ratio, which in turn reveals the possibility of using drop shape to control spreading. The physical mechanisms driving the considered phenomenon are underlined by energy budget analyses and scaling laws. The results are summarised in a two-dimensional diagram linking the drop maximum spreading, minimum height and final shape with different spreading regimes through a single dimensionless parameter, here called the impact number.
Suppose that G is a finite solvable group. Let $t=n_c(G)$ denote the number of orders of nonnormal subgroups of G. We bound the derived length $dl(G)$ in terms of $n_c(G)$. If G is a finite p-group, we show that $|G'|\leq p^{2t+1}$ and $dl(G)\leq \lceil \log _2(2t+3)\rceil $. If G is a finite solvable nonnilpotent group, we prove that the sum of the powers of the prime divisors of $|G'|$ is less than t and that $dl(G)\leq \lfloor 2(t+1)/3\rfloor +1$.
In 1960 Sir Solly Zuckerman proposed the idea of an interdisciplinary department of ‘environmental sciences’ (ENV) for the newly established University of East Anglia (UEA). Prior to this point, the concept of ‘environmental sciences’ was little known: since then, departments and degree courses have rapidly proliferated through universities and colleges around the globe. This paper draws on archival research to explore the conditions and contexts that led to the proposal of a new and interdisciplinary grouping of sciences by Zuckerman. It argues that the activities of Zuckerman and other scientists in Britain during the Second World War and in the post-war period helped to create fertile conditions for a new kind of scientific authority to emerge as a tool of governance and source of policy advice. In particular, the specific challenges of post-war Britain – as addressed through scientific advisers and civil servants – led to the ‘environment’ becoming both the subject of sustained scientific study and an object of concern.
While capillary imbibition in tubes or porous materials has been studied extensively in the past, less attention has been paid to imbibition into a swellable porous material. However, swelling is commonly observed when a polymeric network, such as the cellulose composing paper fibres or sponges, absorbs a solvent. The incompressibility of the fluid leads to an elastic expansion of the polymeric matrix. In a porous material, swelling can affect the geometry of the pores, thus affecting the capillary flow. To describe this complex problem, we propose a model experiment, namely the capillary imbibition in a model pore composed of two parallel and stretched elastomeric fibres. In this configuration, one can observe both the progression of a capillary meniscus and the swelling of the fibres. We show that swelling enables a capillary imbibition for fibres placed further apart than the critical distance existing for non-swelling fibres. In this swelling-dominated regime, we identify a new imbibition dynamic at constant velocity which we rationalize using a linear poro-elastic theory. Finally, we describe the elastocapillary collapse of our model pore which is observed when capillary forces overcome the restoring tension force within the fibres.
Mouse testicular tissue is composed of seminiferous tubules and interstitial tissue. Mammalian spermatogenesis is divided into three stages: spermatocytogenesis (mitotic divisions) in which spermatogonial stem cells (SSCs) turn into spermatocytes, followed by two consecutive meiotic divisions in which spermatocytes form spermatids. Spermatids differentiate into spermatozoa during spermiogenesis. Various factors affect the process of spermatogenesis and the organization of cells in the testis. Any disorder in different stages of spermatogenesis will have negative effects on male fertility. The aim of the current study was to compare the in vitro and in vivo spermatogenesis processes before and after transplantation to azoospermic mice using ultrastructural techniques. In this study, mice were irradiated with single doses of 14 Gy 60Co radiation. SSCs isolated from neonatal mice were cultured in vitro for 1 week and were injected into the seminiferous tubule recipient’s mice. Testicular cells of neonatal mice were cultured in the four groups on extracellular matrix-based 3D printing scaffolds. The transplanted testes (8 weeks after transplantation) and cultured testicular cells in vitro (after 3 weeks) were then processed for transmission electron microscopy studies. Our study’s findings revealed that the morphology and ultrastructure of testicular cells after transplantation and in vitro culture are similar to those of in vivo spermatogenesis, indicating that spermatogenic cell nature is unaltered in vitro.
Long-term contact with English has led to the presence in Guernésiais of a considerable number of lone English-origin lexical items (Jones, 2015). Although the presence of such items was being noted as far back as the nineteenth century, this is the first study to analyse and document them systematically. Using extensive original data, it examines these lexical items in relation to each part of speech and discusses their use in Guernésiais in the broader context of language contact. The study also considers whether, and how, lone English-origin lexical items become assimilated phonologically and morphosyntactically and whether frequency and motivation have a bearing on their usage.
The meridional rank conjecture asks whether the bridge number of a knot in $S^3$ is equal to the minimal number of meridians needed to generate the fundamental group of its complement. In this paper, we investigate the analogous conjecture for knotted spheres in $S^4$. Towards this end, we give a construction to produce classical knots with quotients sending meridians to elements of any finite order in Coxeter groups and alternating groups, which detect their meridional ranks. We establish the equality of bridge number and meridional rank for these knots and knotted spheres obtained from them by twist-spinning. On the other hand, we show that the meridional rank of knotted spheres is not additive under connected sum, so that either bridge number also collapses, or meridional rank is not equal to bridge number for knotted spheres.
Returns to currency carry and momentum compensate for the risk of global interest rate volatility (IRV), with risk exposures explaining 92% of the cross-sectional return variations. This unified explanation stems from its impact on foreign exchange intermediaries. An intermediary-based exchange rate model shows that a higher global IRV increases the uncertainty of future risk-taking and tightens current financial constraints. Position unwinding triggers loss of carry and momentum. Additional empirical results confirm this economic channel. Global IRV risk is also negatively priced in other currency strategies and momentum. The explanatory power is not driven by existing measures of uncertainty or intermediary constraints.