ABSTRACT
The observed distribution of radii for exoplanets shows a bimodal form that can be explained by mass-loss from planetary atmospheres due to high-energy radiation emitted by their host stars. ...The location of the minimum of this radius distribution depends on the mass–radius relation, which in turn depends on the composition of planetary cores. Current studies suggest that super-Earth and mini-Neptune planets have iron-rich and hence largely Earth-like composition cores. This paper explores how non-zero planetary magnetic fields can decrease the expected mass-loss rates from these planets. These lower mass-loss rates, in turn, affect the location of the minimum of the radius distribution and the inferred chemical composition of the planetary cores.
The Nature and Origins of Sub‐Neptune Size Planets Bean, Jacob L.; Raymond, Sean N.; Owen, James E.
Journal of geophysical research. Planets,
January 2021, 2021-Jan, 2021-01-00, 20210101, Letnik:
126, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Planets intermediate in size between the Earth and Neptune, and orbiting closer to their host stars than Mercury does the Sun, are the most common type of planet revealed by exoplanet surveys over ...the last quarter century. Results from NASA's Kepler mission have revealed a bimodality in the radius distribution of these objects, with a relative underabundance of planets between 1.5 and 2.0 R⊕. This bimodality suggests that sub‐Neptunes are mostly rocky planets that were born with primary atmospheres a few percent by mass accreted from the protoplanetary nebula. Planets above the radius gap were able to retain their atmospheres (“gas‐rich super‐Earths”), while planets below the radius gap lost their atmospheres and are stripped cores (“true super‐Earths”). The mechanism that drives atmospheric loss for these planets remains an outstanding question, with photoevaporation and core‐powered mass loss being the prime candidates. As with the mass‐loss mechanism, there are two contenders for the origins of the solids in sub‐Neptune planets: the migration model involves the growth and migration of embryos from beyond the ice line, while the drift model involves inward‐drifting pebbles that coagulate to form planets close‐in. Atmospheric studies have the potential to break degeneracies in interior structure models and place additional constraints on the origins of these planets. However, most atmospheric characterization efforts have been confounded by aerosols. Observations with upcoming facilities are expected to finally reveal the atmospheric compositions of these worlds, which are arguably the first fundamentally new type of planetary object identified from the study of exoplanets.
Plain Language Summary
Planets with radii between that of the Earth and Neptune have been found around other stars in large numbers. It wasn't immediately obvious after their initial discovery what the basic characteristics of these planets are and how they formed because there aren't exact analogs of them in the solar system. Scientists have recently concluded that they are most likely Earth‐like in composition based on measurements of how common objects of different sizes and densities in this regime are. However, there are two classes of these objects. The class of slightly larger objects harbors moderately thick atmospheres composed primarily of hydrogen gas. The other class of smaller objects are thought to have been born with similar atmospheres, but lost them during their subsequent evolution. Both classes of these planets must have formed very soon after the formation of their host stars in order to have started with hydrogen‐dominated atmospheres, but the exact sequence of events leading to the birth of these objects remains uncertain. Efforts to directly study the atmospheres of these objects have been mostly stymied by heavy cloud layers. Observations with new telescopes are expected to yield detailed information on the atmospheres to further our understanding of these objects.
Key Points
Sub‐Neptune planets are rocky bodies that bifurcate into two classes based on their retention or loss of hydrogen‐dominated atmospheres
Sub‐Neptune planets formed within gas‐dominated disks from solids that experienced large‐scale inward movement
Atmospheric characterization of sub‐Neptune planets has been frustrated by the presence of aerosols
Technology is being increasingly integrated into teaching environments in view of enhancing students’ engagement and motivation. In particular, game-based student response systems have been found to ...foster students’ engagement, enhance classroom dynamics and improve overall students’ learning experience. This article presents outcomes of research that examined students’ experience using a game-based student response system, Kahoot!, in an Information Systems Strategy and Governance course at a research-intensive teaching university in New Zealand. We conducted semi-structured interviews with students to learn about the extent to which Kahoot! influence classroom dynamics, motivation and students’ learning process. Key findings revealed that Kahoot! enriched the quality of student learning in the classroom, with the highest influence reported on classroom dynamics, engagement, motivation and improved learning experience. Our findings also suggest that the use of educational games in the classroom is likely to minimise distractions, thereby improving the quality of teaching and learning beyond what is provided in conventional classrooms. Other factors that contributed to students’ enhanced learning included the creation and integration of appropriate content in Kahoot!, providing students with timely feedback, and game-play (gamification) strategies.
► Participants’ perception of CO2 differences were compared for positive and negative framing. ► Negative framing was found effective in highlighting differences between CO2 amounts. ► Applications ...to policy and practice are discussed.
The provision of information about transport-related carbon dioxide (CO2) emissions to the traveler can be seen as an instrument to increase the likelihood of more sustainable choices being made by individuals. However, as transport-related CO2 emissions are largely seen as a ‘social’ cost rather than a ‘private’ cost to the individual, the behavioral engagement with and response to information on environmental effects of travel choices may be limited. It is argued that framing, studied in a range of contexts, can be used to enhance the evaluation of choice attributes and promote more sustainable choices. An experiment is reported that examines the effect of valence framing of amounts of CO2 emissions on the perceived differences between alternative amounts. Through the use of positive and negative terms, the information is framed to focus attention either on the potential of a travel mode to provide environmental benefit (positive frame) or on its potential to reduce environmental loss (negative frame). Survey participants’ estimates of CO2 amounts were compared for positive and negative framing of the same information using an ordered logit model. The findings imply that negative framing is more effective than positive framing in highlighting differences between CO2 amounts of alternative travel modes and therefore is likely to influence travel-related choices.
DISK-FED GIANT PLANET FORMATION Owen, James E.; Menou, Kristen
Astrophysical journal. Letters,
03/2016, Letnik:
819, Številka:
1
Journal Article
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Odprti dostop
ABSTRACT Massive giant planets, such as the ones being discovered by direct imaging surveys, likely experience the majority of their growth through a circumplanetary disk. We argue that the entropy ...of accreted material is determined by boundary layer processes, unlike the "cold-" or "hot-start" hypotheses usually invoked in the core-accretion and direct-collapse scenarios. A simple planetary evolution model illustrates how a wide range of radius and luminosity tracks become possible, depending on details of the accretion process. Specifically, the protoplanet evolves toward "hot-start" tracks if the scale height of the boundary layer is 0.24, a value not much larger than the scale height of the circumplanetary disk. Understanding the luminosity and radii of young giant planets will thus require detailed models of circumplanetary accretion.
Abstract
In 2017, the California-Kepler Survey (CKS) published its first data release (DR1) of high-resolution optical spectra of 1305 planet hosts. Refined CKS planet radii revealed that small ...planets are bifurcated into two distinct populations, super-Earths (smaller than 1.5
R
⊕
) and sub-Neptunes (between 2.0 and 4.0
R
⊕
), with few planets in between (the “radius gap”). Several theoretical models of the radius gap predict variation with stellar mass, but testing these predictions is challenging with CKS DR1 due to its limited
M
⋆
range of 0.8–1.4
M
⊙
. Here we present CKS DR2 with 411 additional spectra and derived properties focusing on stars of 0.5–0.8
M
⊙
. We found that the radius gap follows
R
p
∝
P
m
with
m
= −0.10 ± 0.03, consistent with predictions of X-ray and ultraviolet- and core-powered mass-loss mechanisms. We found no evidence that
m
varies with
M
⋆
. We observed a correlation between the average sub-Neptune size and
M
⋆
. Over 0.5–1.4
M
⊙
, the average sub-Neptune grows from 2.1 to 2.6
R
⊕
, following
R
p
∝
M
⋆
α
with
α
= 0.25 ± 0.03. In contrast, there is no detectable change for super-Earths. These
M
⋆
–
R
p
trends suggest that protoplanetary disks can efficiently produce cores up to a threshold mass of
M
c
, which grows linearly with stellar mass according to
M
c
≈ 10
M
⊕
(
M
⋆
/
M
⊙
). There is no significant correlation between sub-Neptune size and stellar metallicity (over −0.5 to +0.5 dex), suggesting a weak relationship between planet envelope opacity and stellar metallicity. Finally, there is no significant variation in sub-Neptune size with stellar age (over 1–10 Gyr), which suggests that the majority of envelope contraction concludes after ∼1 Gyr.
According to a recent no-go theorem M. Pusey, J. Barrett and T. Rudolph, Nat. Phys. 8, 475 (2012), models in which quantum states correspond to probability distributions over the values of some ...underlying physical variables must have the following feature: the distributions corresponding to distinct quantum states do not overlap. In such a model, it cannot coherently be maintained that the quantum state merely encodes information about underlying physical variables. The theorem, however, considers only models in which the physical variables corresponding to independently prepared systems are independent, and this has been used to challenge the conclusions of that work. Here we consider models that are defined for a single quantum system of dimension d, such that the independence condition does not arise, and derive an upper bound on the extent to which the probability distributions can overlap. In particular, models in which the quantum overlap between pure states is equal to the classical overlap between the corresponding probability distributions cannot reproduce the quantum predictions in any dimension d ≥ 3. Thus any ontological model for quantum theory must postulate some extra principle, such as a limitation on the measurability of physical variables, to explain the indistinguishability of quantum states. Moreover, we show that as d→∞, the ratio of classical and quantum overlaps goes to zero for a class of states. The result is noise tolerant, and an experiment is motivated to distinguish the class of models ruled out from quantum theory.
Summary
Background
Using a monoclonal antibody with greater affinity for IgE than omalizumab, we examined whether more complete suppression of IgE provided greater pharmacodynamic effects, including ...suppression of skin prick responses to allergen.
Objective
To explore the pharmacokinetics, pharmacodynamics and safety of QGE031 (ligelizumab), a novel high‐affinity humanized monoclonal IgG1κ anti‐IgE.
Methods
Preclinical assessments and two randomized, placebo‐controlled, double‐blind clinical trials were conducted in atopic subjects. The first trial administered single doses of QGE031 (0.1–10 mg/kg) or placebo intravenously, while the second trial administered two to four doses of QGE031 (0.2– 4 mg/kg) or placebo subcutaneously at 2‐week intervals. Both trials included an open‐label omalizumab arm.
Results
Sixty of 73 (82%) and 96 of 110 (87%) subjects completed the intravenous and subcutaneous studies, respectively. Exposure to QGE031 and its half‐life depended on the QGE031 dose and serum IgE level. QGE031 had a biexponential pharmacokinetic profile after intravenous administration and a terminal half‐life of approximately 20 days. QGE031 demonstrated dose‐ and time‐dependent suppression of free IgE, basophil FcεRI and basophil surface IgE superior in extent (free IgE and surface IgE) and duration to omalizumab. At Day 85, 6 weeks after the last dose, skin prick wheal responses to allergen were suppressed by > 95% and 41% in subjects treated subcutaneously with QGE031 (2 mg/kg) or omalizumab, respectively (P < 0.001). Urticaria was observed in QGE031‐ and placebo‐treated subjects and was accompanied by systemic symptoms in one subject treated with 10 mg/kg intravenous QGE031. There were no serious adverse events.
Conclusion and Clinical Relevance
These first clinical data for QGE031, a high‐affinity IgG1κ anti‐IgE, demonstrate that increased suppression of free IgE compared with omalizumab translated to superior pharmacodynamic effects in atopic subjects, including those with high IgE levels. QGE031 may therefore benefit patients unable to receive, or suboptimally treated with, omalizumab.
Driven-dissipative quantum many-body systems have attracted increasing interest in recent years as they lead to novel classes of quantum many-body phenomena. In particular, mean-field calculations ...predict limit cycle phases, slow oscillations instead of stationary states, in the long-time limit for a number of driven-dissipative quantum many-body systems. Using a cluster mean-field and a self-consistent Mori projector approach, we explore the persistence of such limit cycles as short range quantum correlations are taken into account in a driven-dissipative Heisenberg model.
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