On the Dominant Lunisolar Perturbations for Long-Term Eccentricity Variation: The Case of Molniya Satellite Orbits

The aim of this work is to investigate the main dominant terms of lunisolar perturbations that affect the orbital eccentricity of a Molniya satellite in the long term. From a practical point of view, these variations are important in the context of space situational awareness—for instance, to model the long-term evolution of artificial debris in a highly elliptical orbit or to design a reentry end-of-life strategy for a satellite in a highly elliptical orbit. The study assumes a doubly averaged model including the Earth’s oblateness effect and the lunisolar perturbations up to the third-order expansion. The work presents three important novelties with respect to the literature. First, the perturbing terms are ranked according to their amplitudes and periods. Second, the perturbing bodies are not assumed to move on circular orbits. Third, the lunisolar effect on the precession of the argument of pericenter is analyzed and discussed. As an example of theoretical a application, we depict the phase space description associated with each dominant term, taken as isolated, and we show which terms can apply to the relevant dynamics in the same region.

Investigating lack of accretion disk eccentricity growth in a global 3D MHD simulation of a superhump system

We present the results of a 3D global magnetohydrodynamic (MHD) simulation of an AM CVn system that was aimed at exploring eccentricity growth in the accretion disc self-consistently from a first principles treatment of the MHD turbulence. No significant eccentricity growth occurs in the simulation. In order to investigate the reasons why, we ran 2D alpha disc simulations with alpha values of 0.01, 0.1, and 0.2, and found that only the latter two exhibit significant eccentricity growth. We present an equation expressing global eccentricity evolution in terms of contributing forces and use it to analyse the simulations. As expected, we find that the dominant term contributing to the growth of eccentricity is the tidal gravity of the companion star. In the 2D simulations, the alpha viscosity directly contributes to eccentricity growth. In contrast, the overall magnetic forces in the 3D simulation damp eccentricity. We also analyzed the mode-coupling mechanism of Lubow, and confirmed that the spiral wave excited by the 3:1 resonance was the dominant contributor to eccentricity growth in the 2D α = 0.1 simulations, but other waves also contribute significantly. We found that the α = 0.1 and 0.2 simulations had more relative mass at larger radii compared to the α = 0.01 and 3D MHD simulation, which also had an effective α of 0.01. This suggests that in 3D MHD simulations without sufficient poloidal magnetic flux, MRI turbulence does not saturate at a high enough α to spread the disc to large enough radii to reproduce the superhumps observed in real systems.

Eisenstein series and an asymptotic for the K-Bessel function

We produce an estimate for the K-Bessel function $$K_{r + i t}(y)$$ K r + i t ( y ) with positive, real argument y and of large complex order $$r+it$$ r + i t where r is bounded and $$t = y \sin \theta $$ t = y sin θ for a fixed parameter $$0\le \theta \le \pi /2$$ 0 ≤ θ ≤ π / 2 or $$t= y \cosh \mu $$ t = y cosh μ for a fixed parameter $$\mu >0$$ μ > 0 . In particular, we compute the dominant term of the asymptotic expansion of $$K_{r + i t}(y)$$ K r + i t ( y ) as $$y \rightarrow \infty $$ y → ∞ . When t and y are close (or equal), we also give a uniform estimate. As an application of these estimates, we give bounds on the weight-zero (real-analytic) Eisenstein series $$E_0^{(j)}(z, r+it)$$ E 0 ( j ) ( z , r + i t ) for each inequivalent cusp $$\kappa _j$$ κ j when $$1/2 \le r \le 3/2$$ 1 / 2 ≤ r ≤ 3 / 2 .

Do we need non-ideal MHD to model protostellar discs?

We investigate and discuss protostellar discs in terms of where the various non-ideal magnetohydrodynamics (MHD) processes are important. We find that the traditional picture of a magnetised disc (where Ohmic resistivity is dominant near the mid-plane, surrounded by a region dominated by the Hall effect, with the remainder of the disc dominated by ambipolar diffusion) is a great oversimplification. In simple parameterised discs, we find that the Hall effect is typically the dominant term throughout the majority of the disc. More importantly, we find that in much of our parameterised discs, at least two non-ideal processes have coefficients within a factor of 10 of one another, indicating that both are important and that naming a dominant term underplays the importance of the other terms. Discs that were self-consistently formed in our previous studies are also dominated by the Hall effect, and the ratio of ambipolar diffusion and Hall coefficients is typically less than 10, suggesting that both terms are equally important and listing a dominant term is misleading. These conclusions become more robust once the magnetic field geometry is taken into account. In agreement with the literature we review, we conclude that non-ideal MHD processes are important for the formation and evolution of protostellar discs. Ignoring any of the non-ideal processes, especially ambipolar diffusion and the Hall effect, yields an incorrect description of disc evolution.

Digital Twins for Cities: A State of the Art Review

During the last decades, a variety of digital tools have been developed to support both the planning and management of cities, as well as the inclusion of civic society. Here, the concept of a Digital Twin – which is rapidly emerging throughout many disciplines due to advances in technology, computational capacities and availability of large amounts of data – plays an important role. In short, a digital twin is a living virtual model, a connected digital representation of a physical system and has been a central concept in the manufacturing industry for the past decades. In this article, we review the terminology of digital twins for cities and identify commonalities and relations to the more established term 3D city models. Our findings indicate an increasing use of the term digital twin in academic literature, both in general and in the context of cities and the built environment. We find that while there is as yet no consensus on the exact definition of what constitutes a digital twin, it is increasingly being used to describe something that is more than a 3D city model (including, e.g. semantic data, real-time sensor data, physical models, and simulations). At the same time, the term has not yet replaced the term 3D city model as the most dominant term in the 3D GIS domain. By looking at grey literature we discuss how digital twins for cities are implemented in practice and present examples of digital twins in a global perspective. Further, we discuss some of the application areas and potential challenges for future development and implementation of digital twins for cities. We conclude that there are significant opportunities for up-scaling digital twins, with the potential to bring benefits to the city and its citizens and clients.

Introduction

This chapter talks about Ivan Sergeevich Turgenev who is known for his renowned ability to describe the natural world. It discusses the three basic, interconnected Russian terms for “nature”: natura, estestvo, and priroda. Natura is the “trait, characteristic, attribute, feature; way of life, that which is natural or inborn.” Estestvo — derived from the Russian word for “is” (est') — meant “all that is; priroda, natura and its order or laws; essence.” Priroda, the dominant term today and for Turgenev, refers to the kind of “nature” that we would readily associate in English with a “nature writer.” In his fiction and nonfiction, Turgenev employed priroda and its forms frequently. The chapter discusses Turgenev's arrest and exile to his country estate in the spring of 1852 that steeped Turgenev in hunting and Aksakovian nature writing.

Aviation Impacts on Fuel Efficiency of a Future More Viscous Atmosphere

Aircraft cruising near the tropopause currently benefit from the highest thermal efficiency and the least viscous (sticky) air, within the lowest 50 km of Earth’s atmosphere. Both advantages wane in a warming climate, because atmospheric dynamic viscosity increases with temperature, in synergy with the simultaneous engine efficiency reduction. Here, skin friction drag, the dominant term for extra aviation fuel consumption in a future warming climate, is quantified by 34 climate models under a strong emissions scenario. Since 1950, the viscosity increase at cruising altitudes (∼200 hPa) reaches ∼1.5% century‒1, corresponding to a total drag increment of ∼0.22% century‒1 for commercial aircraft. Meridional gradients and regional disparities exist, with low to midlatitudes experiencing greater increases in skin friction drag. The North Atlantic corridor (NAC) is moderately affected, but its high traffic volume generates additional fuel cost of ∼3.8 × 107 gallons annually by 2100, compared to 2010. Globally, a normal year after 2100 would consume an extra ∼4 × 106 barrels per year. Intermodel spread is <5% of the ensemble mean, due to high inter–climate model consensus for warming trends at cruising altitudes in the tropics and subtropics. Because temperature is a well-simulated parameter in the IPCC archive, with only a moderate intermodel spread, the conclusions drawn here are statistically robust. Notably, additional fuel costs are likely from the increased vertical shear and related turbulence at NAC cruising altitudes. Increased flight log availability is required to confirm this apparent increasing turbulence trend.

The Eclipse of Form in Roland Barthes’s

This chapter charts the process whereby the text of Barthes’s La Chambre claire sidelines form as a critical concern applicable to photography. An overview of the value system he brings to photography (quite unlike the one he applies to the Novel in the lectures he was delivering contemporaneously) shows that the priority accorded to the referent over the photo as such, to authentication (“ça-a-été”) over representation, and to the disturbing punctum over the disturbed studium, necessarily entails the priority of force over form, not least because each dominant term in these pairs undermines the value of the photograph as something outwardly visual and concretely visible. Force, or intensity, can be tracked not just in the photograph, but also in Barthes’s emotions, whether as beholder of the photo, son in mourning, or essayist repudiating critical sterility, proposing instead to construct a personal phenomenology incorporating the force of affect. A short conclusion via the ideas of René Thom on salient and pregnant forms will suggest a way of bridging the gap between form and force.

The Alternative Augustan Age

“The Augustan Age” is a dominant term in historical, literary, and cultural scholarship, not to mention teaching. This introductory chapter highlights some of the limitations of thinking of a period of many decades and constant change in terms of a single “Augustan age.” It makes the case for looking beyond conventional “key dates” and the figure of Augustus himself to recover the alternative contemporary perspectives and processes of negotiation and compromise. Doing so (as the following chapters demonstrate) reveals the resilience of Roman (republican) culture and the extent to which individuals other than Augustus were able to shape the Augustan principate.

An Investigation of Hydrometeor Latent Cooling upon Convective Cold Pool Formation, Sustainment, and Properties

Downdrafts extending from convective clouds can produce cold pools that propagate outward, sometimes initiating new convection along their leading edges. Models operating at scales requiring convective parameterizations usually lack representation of this detail, and thus fail to predict this convective regeneration and longer episodes of convective activity. Developing such parameterizations requires an improved understanding of the physical drivers of cold pools, and detailed studies of the roles of all the contributing microphysical processes have been lacking. This study utilizes a set of 12 simulations conducted within a single convective environment, but with variability in the microphysical fields produced by varying parameters influencing warm-rain or ice processes. Time-integrated microphysical budgets quantify the contribution of each hydrometeor type to the total latent cooling occurring in the downdrafts that form and sustain the cold pool. The timing of the onset of the cold pool is earlier in cases with a stronger warm rain process, but both graupel and rain were equally as likely to be the dominant hydrometeor in the downdraft first forming the cold pool. Graupel sublimation is the dominant term in sustaining the cold pool in all simulations, but the evaporation of rain has the strongest correlation to the cold pool expansion rate, depth, and intensity. Reconciling the current results with past studies elucidates the importance of considering: graupel sublimation, the latent cooling only in downdrafts contributing to the cold pool, and latent cooling in those downdrafts at altitudes that may be significantly higher than the melting level.