Conceptions of distance are foundational to historical thought, but Mark Salber Phillips gives the idea new subtlety and meaning. He argues that distance is a matter not just of time and space but ...also of form, affect, ideology, and understanding. In this exceptionally wide-ranging study, Phillips examines Renaissance, Enlightenment, and contemporary histories, as well as a broad spectrum of historical genres-including local history, literary history, counter-factual fiction, history painting, and museology.
"On Historical Distanceis a fascinating and very important book that should be read by all historians. Beautifully written in elegant, economical and engaging prose, the book wears its considerable learning very lightly. A deeply original, challenging and thought-provoking study of the evolving history of history by one of our leading historians of historiography, this book should provoke a lively debate among historians and should be assigned as essential reading for classes on historical methods and historiography."-John Marshall, John Hopkins University
Ecosystems have recently emerged as a visible stream in organization and management research. The ecosystem concept promises a broader, systems view of organizational and technological phenomena ...beyond traditional firm, value chain or network boundaries. However, adopting an ecosystem approach presents a range of methodological challenges for researchers, including how to set boundaries for the ecosystems, as well as how to examine their structure and relationships, as well as to explain the inherent dynamics and co-evolution. Based upon on a complex adaptive systems lens, this study proposes a theoretically grounded but pragmatic approach to address these challenges. The proposed methodological framework facilitates exploration of the conceptual, structural and temporal dimensions of ecosystem research design. An illustrative example is also included to showcase the framework's applicability.
•Ecosystem research suffers from ambiguous conceptualizations and foundations.•To this end, we develop a complex adaptive systems approach to study ecosystems.•We introduce a framework with conceptual, structural and temporal dimensions.•The framework helps design better grounded and more holistic studies in the field.
Abstract
We present 888 visual-wavelength spectra of 122 nearby type II supernovae (SNe II) obtained between 1986 and 2009, and ranging between 3 and 363 days post-explosion. In this first paper, we ...outline our observations and data reduction techniques, together with a characterization based on the spectral diversity of SNe II. A statistical analysis of the spectral matching technique is discussed as an alternative to nondetection constraints for estimating SN explosion epochs. The time evolution of spectral lines is presented and analyzed in terms of how this differs for SNe of different photometric, spectral, and environmental properties: velocities, pseudo-equivalent widths, decline rates, magnitudes, time durations, and environment metallicity. Our sample displays a large range in ejecta expansion velocities, from ∼9600 to ∼1500 km s
−1
at 50 days post-explosion with a median
value of 7300 km s
−1
. This is most likely explained through differing explosion energies. Significant diversity is also observed in the absolute strength of spectral lines, characterized through their pseudo-equivalent widths. This implies significant diversity in both temperature evolution (linked to progenitor radius) and progenitor metallicity between different SNe II. Around 60% of our sample shows an extra absorption component on the blue side of the
P-Cygni profile (“Cachito” feature) between 7 and 120 days since explosion. Studying the nature of Cachito, we conclude that these features at early times (before ∼35 days) are associated with Si
ii
, while past the middle of the plateau phase they are related to high velocity (HV) features of hydrogen lines.
ABSTRACT
We present a publicly available library of model atmospheres with radiative-convective equilibrium pressure–temperature (P-T) profiles fully consistent with equilibrium chemical abundances, ...and the corresponding emission and transmission spectrum with R ∼ 5000 at 0.2 µm decreasing to R ∼ 35 at 30 µm, for 89 hot Jupiter exoplanets, for four recirculation factors, six metallicities, and six C/O ratios. We find the choice of condensation process (local/rainout) alters the P-T profile and thereby the spectrum substantially, potentially detectable by James Webb Space Telescope. We find H− opacity can contribute to form a strong temperature inversion in ultrahot Jupiters for C/O ratios ≥ 1 and can make transmission spectra features flat in the optical, alongside altering the entire emission spectra. We highlight how adopting different model choices such as thermal ionization, opacities, line-wing profiles and the methodology of varying the C/O ratio, effects the P-T structure, and the spectrum. We show the role of Fe opacity to form primary/secondary inversion in the atmosphere. We use WASP-17b and WASP-121b as test cases to demonstrate the effect of grid parameters across their full range, while highlighting some important findings, concerning the overall atmospheric structure, chemical transition regimes, and their observables. Finally, we apply this library to the current transmission and emission spectra observations of WASP-121b, which shows H2O and tentative evidence for VO at the limb, and H2O emission feature indicative of inversion on the dayside, with very low energy redistribution, thereby demonstrating the applicability of library for planning and interpreting observations of transmission and emission spectrum.
Here we present a publicly available database of opacities for molecules of astrophysical interest named ExoMolOP that has been compiled for over 80 species, and is based on the latest line list data ...from the ExoMol, HITEMP, and MoLLIST databases. These data are generally suitable for characterising high-temperature exoplanet or cool stellar and substellar atmospheres, and have been computed at a variety of pressures and temperatures, with a few molecules included at room temperature only from the HITRAN database. The data are formatted in different ways for four different exoplanet atmosphere retrieval codes; ARCiS, TauREx, NEMESIS, and petitRADTRANS, and include both cross sections (at
R
=
λ
/Δ
λ
= 15000) and
k
-tables (at
R
=
λ
/Δ
λ
= 1000) for the 0.3–50
μ
m wavelength region. Opacity files can be downloaded and used directly for these codes. Atomic data for alkali metals Na and K are also included, using data from the NIST database and the latest line shapes for the resonance lines. Broadening parameters have been taken from the literature where available, or have been estimated from the parameters of a known molecule with similar molecular properties where no broadening data are available.
Abstract
Measurements of the C/O ratio in brown dwarfs are lacking, in part due to past models adopting solar C/O only. We have expanded the
ATMO 2020
atmosphere model grid to include nonsolar ...metallicities and C/O ratios in the T dwarf regime. We change the C/O ratio by altering either the carbon or oxygen elemental abundances, and we find that nonsolar abundances of these elements can be distinguished based on the shapes of the
H
and
K
bands. We compare these new models with medium-resolution (
R
≈ 1700), near-infrared (0.8–2.4
μ
m) Gemini Near-Infrared Spectrograph (GNIRS) spectra of three benchmark late-T dwarfs, GJ 570D, HD 3651B, and Ross 458C. We find solar C/O ratios and best-fitting parameters (
T
eff
,
log
(
g
)
,
Z
) broadly consistent with other analyses in the literature based on low-resolution (
R
∼ 100) data. The model-data discrepancies in the near-infrared spectra are consistent across all three objects. These discrepancies are alleviated when fitting the
Y
,
J
,
H
, and
K
bands individually, but the resulting best-fit parameters are inconsistent and disagree with the results from the full spectrum. By examining the model atmosphere properties we find this is due to the interplay of gravity and metallicity on H
2
–H
2
collisionally induced absorption. We therefore conclude that there are no significant issues with the molecular opacity tables used in the models at this spectral resolution. Instead, deficiencies are more likely to lie in the model assumptions regarding the thermal structures. Finally, we find a discrepancy between the GNIRS, SpeX, and other near-infrared spectra in the literature of Ross 458C, indicating potential spectroscopic variability.
The recent explosion in machine learning efforts in the quality assurance (QA) space has produced a variety of proofs‐of‐concept many with promising results. Expected outcomes of model implementation ...include improvements in planning time, plan quality, advanced dosimetric QA, predictive machine maintenance, increased safety checks, and developments key for new QA paradigms driven by adaptive planning. In this article, we outline several areas of research and discuss some of the unique challenges each area presents.
Although it is relatively straightforward to measure the ionic, atomic, molecular, and particle emission features from laser ablation plumes, the associated kinetic and thermodynamic development ...leading to molecular and nanocluster formation remain one of the most important topics of analytical chemistry and material science. Very little is known, for instance, about the evolutionary paths of molecular and nanocluster formation and its relation to laser plume hydrodynamics. This is, to a large extent; due to the complexity of numerous physical processes that coexist in a transient laser-plasma system. Here, we report the formation mechanisms of molecules during complex interactions of a laser-produced plasma plume expanding from a high purity aluminum metal target into ambient air. It is found that the plume hydrodynamics plays a great role in redefining the plasma thermodynamics and molecular formation. Early in the plasma expansion, the generated shock wave at the plume edge acts as a barrier for the combustion process and molecular formation is prevalent after the shock wave collapse. The temporally and spatially resolved contour mapping of atoms and molecules in laser ablation plumes highlight the formation routes and persistence of species in the plasma and their relation to plume hydrodynamics.
Abstract
We present comprehensive orbital analyses and dynamical masses for the substellar companions Gl 229 B, Gl 758 B, HD 13724 B, HD 19467 B, HD 33632 Ab, and HD 72946 B. Our dynamical fits ...incorporate radial velocities, relative astrometry, and, most importantly, calibrated Hipparcos-Gaia EDR3 accelerations. For HD 33632 A and HD 72946 we perform three-body fits that account for their outer stellar companions. We present new relative astrometry of Gl 229 B with Keck/NIRC2, extending its observed baseline to 25 yr. We obtain a <1% mass measurement of 71.4 ± 0.6
M
Jup
for the first T dwarf Gl 229 B and a 1.2% mass measurement of its host star (0.579 ± 0.007
M
⊙
) that agrees with the high-mass end of the M-dwarf mass–luminosity relation. We perform a homogeneous analysis of the host stars’ ages and use them, along with the companions’ measured masses and luminosities, to test substellar evolutionary models. Gl 229 B is the most discrepant, as models predict that an object this massive cannot cool to such a low luminosity within a Hubble time, implying that it may be an unresolved binary. The other companions are generally consistent with models, except for HD 13724 B, which has a host star activity age 3.8
σ
older than its substellar cooling age. Examining our results in context with other mass–age–luminosity benchmarks, we find no trend with spectral type but instead note that younger or lower-mass brown dwarfs are overluminous compared to models, while older or higher-mass brown dwarfs are underluminous. The presented mass measurements for some companions are so precise that the stellar host ages, not the masses, limit the analysis.
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