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The flow field of a bluff body, a circular disk, that moves horizontally in a stratified environment is studied using large-eddy simulations. Five levels of stratification (body Froude numbers of ${{Fr}} = 0.5, 1, 1.5, 2$ and $5$) are simulated at Reynolds number of ${{Re}} = 5000$ and Prandtl number of $Pr =1$. A higher ${{Re}} = 50\,000$ database at ${{Fr}} = 2, 10$ and $Pr =1$ is also examined for comparison. The wavelengths and amplitudes of steady lee waves are compared with a linear-theory analysis. Excellent agreement is found over the entire range of ${{Fr}}$ if an ‘equivalent body’ that includes the separation region is employed for the linear theory. For asymptotically large distances, the velocity amplitude varies theoretically as ${{Fr}}^{-1}$ but a correction owing to the dependence of the separation zone on ${{Fr}}$ is needed. The wake waves propagate in a narrow band of angles with the vertical, and have a wavelength that increases with increasing ${{Fr}}$. The envelope of wake waves, demarcated using buoyancy variance, exhibits self-similar behaviour. The higher ${{Re}}$ results are consistent with the buoyancy effects exhibited at the lower ${{Re}}$. The wake wave energy is larger at ${{Re}} = 50\,000$. Nevertheless, independent of ${{Fr}}$ and ${{Re}}$, the ratio of the wake wave potential energy to the wake turbulent energy increases to approximately 0.6–0.7 in the non-equilibrium stage showing their energetic importance besides suggesting universality in this statistic. There is a crossover of energetic dominance of lee waves at ${{Fr}} <2$ to wake-wave dominance at ${{Fr}} \approx 5$.
Recently, several philosophers have argued that, when faced with moral uncertainty, we ought to choose the option with the maximal expected choiceworthiness (MEC). This view has been challenged on the grounds that it is implausibly demanding. In response, those who endorse MEC have argued that we should take into account the all-things-considered choiceworthiness of our options. I argue that this gives rise to another problem: acts that we consider to be supererogatory are rendered impermissible, and acts that we consider to be suberogatory are rendered obligatory, under MEC. I suggest a way to reformulate MEC to solve this problem.
Emerging societal expectations from biomedical research and intensifying international scientific competition are becoming existential matters. Based on a review of pertinent evidence, this article analyzes challenges and formulates public policy recommendations for improving productivity and impact of life sciences. Critical risks include widespread quality defects of research, particularly non-reproducible results, and narrow access to scientifically sound information giving advantage to health misinformation. In funding life sciences, the simultaneous shift to nondemocratic societies is an added challenge. Simply spending more on research will not be enough in the global competition. Considering the pacesetter role of the federal government, five national policy recommendations are put forward: (i) funding projects with comprehensive expectations of reproducibility; (ii) public–private partnerships for contemporaneous quality support in laboratories; (iii) making research institutions accountable for quality control; (iv) supporting new quality filtering standards for scientific journals and repositories, and (v) establishing a new network of centers for scientific health communications.
We investigate voter preferences for changes in voting rules, focusing specifically on the creation of citizen-initiative processes that were originally adopted in South Dakota in 1898 and eventually enacted by half of the states. Various claims have been advanced about why the process was adopted and who supported or opposed it, but without presenting evidence from referenda where voters approved the creation of the process. We test these claims by examining county-level election returns from South Dakota’s 1898 referendum that created the first statewide initiative process in the United States. We find that support for the initiative process was generally higher among groups that are disadvantaged in various ways by existing representative institutions and perceive advantages in creating direct democratic institutions capable of bypassing representative processes. These findings stand in contrast to the notion that the adoption of constitutional rules will be relatively free from calculations rooted in self-interest and perceived advantage from the rules changes.
This paper examines how credit guarantees and government subsidies impact investment in a regime-switching model. We provide new explicit pricing formulas for a general standard asset. Almost all common corporate securities’ prices can be easily derived by the explicit formulas though project cash flows are driven by both a Brownian motion and a two-state Markov chain. We provide a method about how governments should specify a proper tax subsidy standard for a given tax rate to motivate a firm to invest in a project in the way they wish. If the tax subsidy is sufficiently high (low), an overinvestment (underinvestment) occurs. The higher the tax rate, the more significant the overinvestment (underinvestment). We pin down the subsidy amount required for motivating a firm to invest immediately and fix the optimal capital structure with government subsidies.
This study investigates the interaction between a freely rising, deformable bubble and a freely settling particle of the same size due to gravity. Initially, an in-line configuration is considered while varying the Bond, Galilei and Archimedes numbers. The study shows that as the bubble and particle approach each other, a liquid film forms between them that undergoes drainage. The formation of the liquid film leads to dissipation of kinetic energy, and for sufficiently large bubble velocities, particle flotation takes place. Increasing the Bond number causes the bubble to deform more severely, which may allow the particle to pass through the bubble as it ruptures. This work also considers an offset configuration, which shows that the bubble slides away from the particle, affecting its settling trajectory.
Transonic aeroelasticity remains a significant challenge in aerospace. The coupling mechanism of aeroelastic problems involving the coexistence of fluid modes and multiple structural modes still needs further investigation. For this purpose, we analysed the dynamic characteristic of a two-degree-of-freedom (2DOF) NACA0012 airfoil in pre-buffet flow. First, we constructed an aeroelastic reduced-order model, which can represent near-unstable transonic flow using the dominant fluid mode. Then, the flutter mechanism was investigated by studying the main eigenvalues of the model that vary with the natural pitching frequency. The results revealed that the existence of the fluid mode transitions the transonic flutter type from coupled-mode flutter to single-DOF (SDOF) flutter, which leads to a reduction in the flutter boundary. Under the effect of the fluid mode, the system produces six aeroelastic phenomena at different structural natural frequencies, including SDOF heaving/pitching flutter, heaving/pitching instability within coupled-mode flutter, forced vibration and stable state. Moreover, we identified two types of SDOF flutter in the 2DOF system. The first type corresponds to the traditional SDOF flutter, where the coupling of other modes has a small impact on the system's stability in most cases. However, within specific ranges of natural frequencies, this type of SDOF flutter may disappear due to coupling with other modes. The second type of SDOF flutter is characterized by strong coupling dominated by the unstable mode. It arises from the interaction among the flow, heaving and pitching modes, and does not manifest in the absence of any of these modes.
Unveiling the pressure‒temperature path of low-grade metamorphic rocks is challenging because of the occurrence of detrital minerals and high-variance mineral assemblages (i.e. chlorite–white mica–quartz). This paper is an attempt to reconstruct the pressure–temperature history on metapelites from a low-grade metamorphic unit, i.e. the Cabanaira Unit, located in the Marguareis Massif (Western Ligurian Alps, Italy). In order to obtain the most robust result possible, multi-equilibrium thermobarometry, forward modelling and crystallochemical index measurements are used together to reconstruct a pressure–temperature path, with consideration of the strengths and weaknesses of these methods.
This multidisciplinary approach allowed us to reconstruct the metamorphic evolution of the unit of interest, characterised by a pressure peak reached under low-temperature conditions (0.85–0.68 GPa and 250–285°C) followed by decompressional warming (low pressure–high temperature, 0.4-0.6 GPa and 300–335°C).
This pressure‒temperature path is consistent with the tectonic evolution of the investigated area proposed by previous studies, where a geological scenario in which the Cabanaira Unit experienced subduction-related processes was postulated, even if the reasons for warming remain unclear.
Multi-equilibrium thermobarometry is considered to be the most suitable method to unravel the metamorphic history of low-grade rocks, whereas forward thermodynamic modelling and the calculation of crystallochemical indexes seem to resolve only some segments of the pressure‒temperature path.
Five typical metal cations (i.e. Na+, K+, Ca2+, Mg2+ and Al3+) were selected as representatives to study the influence of metal cations on the dissolution and transformation of biotite. This work focussed on the mineralogical features of transformation products and phase transformation mechanisms by utilising modern spectroscopic methods and micro-beam characterisation techniques. In comparison with a control system, K+ inhibited the dissolution and transformation of biotite, leading to the generation of amorphous iron hydroxides on the biotite surface. Na+, Mg2+ and Ca2+ promoted the dissolution of biotite but inhibited its transformation into kaolinite, with the Na system producing sodium-bearing biotite, vermiculite, hematite and a small amount of kaolinite, and the Mg and Ca systems producing mainly vermiculite, chlorite and hematite. Al3+ notably accelerated the dissolution and transformation of biotite, resulting in well-crystallised kaolinite and hematite. Furthermore, metal cations changed the formation mechanism of kaolinite by altering the dissolution rate of biotite. Within the blank system, biotite dissolved slowly, with elements (i.e. Al and Si) accumulating on the biotite surface and growing epitaxially into kaolinite; whereas in the Al system, the rapid dissolution of biotite provided a large amount of Si, which combined with Al in the solution, forming kaolinite via a dissolution–recrystallisation process. In addition, the exchange reactions of metal-cation–K+ and the competitive adsorption of metal-cation–proton simultaneously constrained the dissolution process of biotite. This work offers a theoretical basis for an in-depth comprehension of the factors influencing biotite weathering and new insights into the evolution of clay minerals in terrestrial surface environments.
The penetration of a spherical vortex into turbulence is studied theoretically and experimentally. The characteristics of the vortex are first analysed from an integral perspective that reconciles the far-field dipolar flow with the near-field source flow. The influence of entrainment on the vortex drag force is elucidated, extending the Maxworthy (J. Fluid Mech., vol. 81, 1977, pp. 465–495) model to account for turbulent entrainment into the vortex movement and vortex penetration into an evolving turbulent field. The physics are explored numerically using a spherical vortex (initial radius $R_0$, speed $U_{v0}$), characterised by a Reynolds number $Re_0(=2R_0U_{v0}/\nu$, where $\nu$ is the kinematic viscosity) of 2000, moving into decaying homogeneous turbulence (root-mean-square $u_0$, integral scale $L$) with turbulent intensity $I_t=u_0/U_{v0}$. When the turbulence is absent ($I_t=0$), a wake volume flux leads to a reduction of vortex impulse that causes the vortex to slow down. In the presence of turbulence ($I_t> 0$), the loss of vortical material is enhanced and the vortex speed decreases until it is comparable to the local turbulent intensity and quickly fragments, penetrating a distance that scales as $I_t^{-1}$. In the experimental study, a vortex ($Re_0\sim 1490\unicode{x2013}5660$) propagating into a statistically steady, spatially varying turbulent field ($I_{ve}=0.02$ to 0.98). The penetration distance is observed to scale with the inverse of the turbulent intensity. Incorporating the spatially and temporally varying turbulent fields into the integral model gives a good agreement with the predicted trend of the vortex penetration distance with turbulent intensity and insight into its dependence on the structure of the turbulence.
Since 2017, Republican lawmakers in a growing number of US states have formed ideological intraparty organizations, modeled after the US House Freedom Caucus, that seek to move state policy further rightward. What explains the appearance of these state freedom caucuses, and what kinds of lawmakers are more likely to join them? We show that the creation of these caucuses was initially motivated by concerns that state-level legislative Republican parties are too ideologically heterogeneous but has since been driven by conservative entrepreneurs seeking to spread freedom caucuses nationally. We also provide evidence that conservative legislators are more likely to join a new state freedom caucus, as one would expect, but also that, in a few states, lawmakers who are more electorally vulnerable lawmakers or lack internal influence have also been more likely to join. These findings underscore how state-level ideological caucuses can appeal to members’ multiple goals and serve as instruments of vertical polarization in a federal system.
ATO4 compounds are a class of oxides which includes the rare earth element (REE) bearing phosphates and arsenates, REEPO4 and REEAsO4. In this study, we have investigated the isothermal high-pressure and the isobaric high-temperature behaviour of natural samples of xenotime-(Y) (ideally YPO4), chernovite-(Y) (YAsO4) and monazite-(Ce) (CePO4) from the hydrothermal veins cropping out at Mt. Cervandone in the Western Italian Alps. Experimental data based on in situ X-ray diffraction (both single-crystal and powder techniques with conventional or synchrotron radiation) have allowed us to fit the unit-cell volumes and axial thermal and compressional evolution and provide a suite of refined thermo-elastic parameters. A comprehensive analysis of the role played by the crystal chemistry on the thermo-elastic response of these minerals is discussed, along with the description of the main crystal-structural deformation mechanisms for both the zircon (xenotime and chernovite) and monazite (monazite) structural types. Pressure-induced phase transitions of xenotime-(Y) and chernovite-(Y) are discussed and compared with previous literature data, whereas a change in the compressional behaviour of monazite-(Ce) at ∼18 GPa, involving an increase in the coordination number of the REE-hosting A site, is presented and discussed.
Oda’s problem, which deals with the fixed field of the universal monodromy representation of moduli spaces of curves and its independence with respect to the topological data, is a central question of anabelian arithmetic geometry. This paper emphasizes the stack nature of this problem by establishing the independence of monodromy fields with respect to finer special loci data of curves with symmetries, which we show provides a new proof of Oda’s prediction.
Skeletal muscle is of great importance for human activity and quality of life, as its loss contributes greatly to immobilisation, especially for aged individuals. An increased dietary intake of antioxidant vitamins may be beneficial for muscle loss because of ageing. However, the quantitative relationship between total antioxidant capacity (TAC) of antioxidant vitamins and muscle mass is undetermined. Totally, 4009 participants from the National Health and Nutrition Examination Survey (NHANES) were included. Multivariate linear regression analysis was performed with demographic, lifestyle and dietary intake adjustment factors. The dose saturation effect was also determined by a saturation effect analysis. Subgroup analysis was performed for age and sex. In the fully adjusted model, per unit increase of dietary TAC was associated with an increase of 0·018 g/kg appendicular lean mass (95 % CI 0·007, 0·029), 0·014 g/kg trunk lean mass (95 % CI 0·004, 0·024) and 0·035 g/kg total lean mass (95 % CI 0·014, 0·055). TAC was associated with a decrease of 0·004 kg/kg total percent fat (95 % CI −0·006, −0·002), 0·005 kg/kg trunk percent fat (95 % CI −0·007, −0·002) and 0·003 kg/m2 BMI (95 % CI −0·006, −0·001) at the same time. Subgroup analysis indicated that women and adults < 50 years may experience the most significant association between TAC and skeletal muscle mass. We revealed a positive correlation between TAC and lean body mass and a negative association between TAC and body fat and BMI. Saturation values were found among people aged 40–59 years. Age and sex mediate these associations.
We study Toeplitz operators on the space of all real analytic functions on the real line and the space of all holomorphic functions on finitely connected domains in the complex plane. In both cases, we show that the space of all Toeplitz operators is isomorphic, when equipped with the topology of uniform convergence on bounded sets, with the symbol algebra. This is surprising in view of our previous results, since we showed that the symbol map is not continuous in this topology on the algebra generated by all Toeplitz operators. We also show that in the case of the Fréchet space of all holomorphic functions on a finitely connected domain in the complex plane, the commutator ideal is dense in the algebra generated by all Toeplitz operators in the topology of uniform convergence on bounded sets.