bluuebunny/crossref_metadata_2025 huggingface dataset:
Still-Life as Portrait in Early Modern Italy
Authors: Lev-er Ornat
Published: June 2021

Still-Life as Portrait in Early Modern Italy centers on the still-life compositions created by Evaristo Baschenis and Bartolomeo Bettera, two 17th-century painters living and working in the Italian city of Bergamo. This highly original study explores how these paintings form a dynamic network in which artworks, musical instruments, books, and scientific apparatuses constitute links to a dazzling range of figures and sources of knowledge. Putting into circulation a wealth of cultural information and ideas and mapping a complex web of social and intellectual relations, these works paint a portrait of both their creators and their patrons, while enacting a lively debate among humanist thinkers, aristocrats, politicians, and artists. The unique contribution of this groundbreaking study is that it identifies for the first time these intellectually rich concepts that arise from these fascinating still-life paintings, a genre considered as "low". Engaging with literary blockbusters and banned books, theatrical artifice and music, and staging a war among the arts, Baschenis and Bettera capture the latest social intrigues, political rivalries, intellectual challenges, and scientific innovations of their time. In doing so, they structure an unstable economy of social, aesthetic, and political values that questions the notion of absolute truth, while probing the distinctions between life and artifice, meaningless marks and meaningful signs.
Democratic Accountability in Times of Crisis: Executive Power, Fiscal Policy and COVID-19
Authors: Lozano Maritza , Atkinson Michael , Mou Haizhen
Published: June 2021

We examine the performance of four parliamentary democracies – Canada, Australia, New Zealand and the UK – as they confront the need for a substantial fiscal policy response to the COVID-19 pandemic. Our research covers the period 1 January 2020 to 30 June 2020. We score the four countries on nine components of democratic accountability using Mark Philp's distinction between formal and political accountability. We conclude, first, that to appreciate the nuanced character of accountability, it is important to have a set of operational measures that identify specific aspects of performance. Second, preparation is important for resilience: countries that demonstrated strong accountability before the pandemic maintained relatively high accountability standards during the crisis; weaker accountability mechanisms showed less resistance to the expanding power of the executive. Finally, it is easier to be accountable when outcomes are favourable, but favourable outcomes include adherence to the norms of democratic accountability.
Hospital capacities and shortages of healthcare resources among US hospitals during the coronavirus disease 2019 (COVID-19) pandemic, National Healthcare Safety Network (NHSN), March 27–July 14, 2020
Authors: Wu Hsiu , Soe Minn M. , Konnor Rebecca , Dantes Raymund , Haass Kathryn , Dudeck Margaret A. , Gross Cindy , Leaptrot Denise , Sapiano Mathew R. P. , Allen-Bridson Katherine , Wattenmaker Lauren , Peterson Kelly , Lemoine Kent , Chernetsky Tejedor Sheri , Edwards Jonathan R. , Pollock Daniel , Benin Andrea L. ,   for the National Healthcare Safety Network
Published: June 2021

During March 27–July 14, 2020, the Centers for Disease Control and Prevention’s National Healthcare Safety Network extended its surveillance to hospital capacities responding to COVID-19 pandemic. The data showed wide variations across hospitals in case burden, bed occupancies, ventilator usage, and healthcare personnel and supply status. These data were used to inform emergency responses.
Risk-sensitive average continuous-time Markov decision processes with unbounded transition and cost rates
Authors: Guo Xin , Huang Yonghui
Published: June 2021

This paper considers risk-sensitive average optimization for denumerable continuous-time Markov decision processes (CTMDPs), in which the transition and cost rates are allowed to be unbounded, and the policies can be randomized history dependent. We first derive the multiplicative dynamic programming principle and some new facts for risk-sensitive finite-horizon CTMDPs. Then, we establish the existence and uniqueness of a solution to the risk-sensitive average optimality equation (RS-AOE) through the results for risk-sensitive finite-horizon CTMDPs developed here, and also prove the existence of an optimal stationary policy via the RS-AOE. Furthermore, for the case of finite actions available at each state, we construct a sequence of models of finite-state CTMDPs with optimal stationary policies which can be obtained by a policy iteration algorithm in a finite number of iterations, and prove that an average optimal policy for the case of infinitely countable states can be approximated by those of the finite-state models. Finally, we illustrate the conditions and the iteration algorithm with an example.
Gibbs partitions, Riemann–Liouville fractional operators, Mittag–Leffler functions, and fragmentations derived from stable subordinators
Authors: Ho Man-Wai , James Lancelot F. , Lau John W.
Published: June 2021

Pitman (2003), and subsequently Gnedin and Pitman (2006), showed that a large class of random partitions of the integers derived from a stable subordinator of index$\alpha\in(0,1)$have infinite Gibbs (product) structure as a characterizing feature. The most notable case are random partitions derived from the two-parameter Poisson–Dirichlet distribution,$\textrm{PD}(\alpha,\theta)$, whose corresponding$\alpha$-diversity/local time have generalized Mittag–Leffler distributions, denoted by$\textrm{ML}(\alpha,\theta)$. Our aim in this work is to provide indications on the utility of the wider class of Gibbs partitions as it relates to a study of Riemann–Liouville fractional integrals and size-biased sampling, and in decompositions of special functions, and its potential use in the understanding of various constructions of more exotic processes. We provide characterizations of general laws associated with nested families of$\textrm{PD}(\alpha,\theta)$mass partitions that are constructed from fragmentation operations described in Donget al.(2014). These operations are known to be related in distribution to various constructions of discrete random trees/graphs in [n], and their scaling limits. A centerpiece of our work is results related to Mittag–Leffler functions, which play a key role in fractional calculus and are otherwise Laplace transforms of the$\textrm{ML}(\alpha,\theta)$variables. Notably, this leads to an interpretation within the context of$\textrm{PD}(\alpha,\theta)$laws conditioned on Poisson point process counts over intervals of scaled lengths of the$\alpha$-diversity.
Bounds for expected supremum of fractional Brownian motion with drift
Authors: Bisewski Krzysztof , Dębicki Krzysztof , Mandjes Michel
Published: June 2021

We provide upper and lower bounds for the mean$\mathscr{M}(H)$of$\sup_{t\geq 0} \{B_H(t) - t\}$, with$B_H(\!\cdot\!)$a zero-mean, variance-normalized version of fractional Brownian motion with Hurst parameter$H\in(0,1)$. We find bounds in (semi-) closed form, distinguishing between$H\in(0,\frac{1}{2}]$and$H\in[\frac{1}{2},1)$, where in the former regime a numerical procedure is presented that drastically reduces the upper bound. For$H\in(0,\frac{1}{2}]$, the ratio between the upper and lower bound is bounded, whereas for$H\in[\frac{1}{2},1)$the derived upper and lower bound have a strongly similar shape. We also derive a new upper bound for the mean of$\sup_{t\in[0,1]} B_H(t)$,$H\in(0,\frac{1}{2}]$, which is tight around$H=\frac{1}{2}$.
TRACKING THE MUTANT: FORECASTING AND NOWCASTING COVID-19 IN THE UK IN 2021
Authors: Harvey Andrew , Kattuman Paul , Thamotheram Craig
Published: June 2021

A new class of time series models is used to track the progress of the COVID-19 epidemic in the UK in early 2021. Models are fitted to England and the regions, as well as to the UK as a whole. The growth rate of the daily number of cases and the instantaneous reproduction number are computed regularly and compared with those produced by SAGE. The results from figures published each day are compared with results based on figures by specimen date, which may be more accurate but are subject to substantial revisions. It is then shown how data from the two different sources can be combined in bivariate models.
THE VALUE OF ROBUST STATISTICAL FORECASTS IN THE COVID-19 PANDEMIC
Authors: Castle Jennifer L. , Doornik Jurgen A. , Hendry David F.
Published: June 2021

The Covid-19 pandemic has put forecasting under the spotlight, pitting epidemiological models against extrapolative time-series devices. We have been producing real-time short-term forecasts of confirmed cases and deaths using robust statistical models since 20 March 2020. The forecasts are adaptive to abrupt structural change, a major feature of the pandemic data due to data measurement errors, definitional and testing changes, policy interventions, technological advances and rapidly changing trends. The pandemic has also led to abrupt structural change in macroeconomic outcomes. Using the same methods, we forecast aggregate UK unemployment over the pandemic. The forecasts rapidly adapt to the employment policies implemented when the UK entered the first lockdown. The difference between our statistical and theory based forecasts provides a measure of the effect of furlough policies on stabilising unemployment, establishing useful scenarios had furlough policies not been implemented.
What We Talk about When We Talk about Poverty: Culture and Welfare State Development in Britain, Denmark and France
Authors: Martin Cathie , Chevalier Tom
Published: June 2021

Why did historical anti-poverty programs in Britain, Denmark and France differ so dramatically in theirgoals,beneficiariesandagentsfor addressing poverty? Different cultural views of poverty contributed to how policy makers envisioned anti-poverty reforms. Danish elites articulated social investments in peasants as necessary to economic growth, political stability and societal strength. British elites viewed the lower classes as a challenge to these goals. The French perceived the poor as an opportunity for Christian charity. Fiction writers are overlooked political agents who engage in policy struggles. Collectively, writers contribute to a country's distinctive ‘cultural constraint’, or symbols and narratives, which appears in the national-level aggregation of literature. To assess cross-national variations in cultural depictions of poverty, this article uses historical case studies and quantitative textual analyses of 562 British, 521 Danish and 498 French fictional works from 1770 to 1920.
Assessment of non-communicable disease related lifestyle risk factors among adult population in Bangladesh
Authors: Hossain Md. Belal , Parvez Mahmood , Islam Mir Raihanul , Evans Hala , Mistry Sabuj Kanti
Published: June 2021

Non-communicable diseases (NCDs), which can largely be prevented by controlling avoidable lifestyle-related risk factors, are rapidly penetrating the entire world, including developing countries. The present study aimed to assess NCD lifestyle risk factors among the adult population in Bangladesh. The data used in the study were collected as part of a population-based cross-sectional survey covering rural and urban areas of Bangladesh conducted in 2015–16 (N=11,982 adults aged ≥35 years). The lifestyle factors considered were diet (daily fruit and vegetable consumption and extra salt intake with meals), sleeping patterns, smoking, smokeless tobacco consumption, and physical activity. The study found that approximately 18.5% of participants had a non-daily consumption of fruit or vegetables, 46.6% used extra salt with their meals, 11.8% reported sleeping <7 hours daily, 25.7% smoked tobacco, 60.9% used smokeless tobacco and 69.7% were less physically active. The prevalence of improper lifestyle practices relevant to NCDs, such as an inadequate diet, poor sleeping pattern, tobacco consumption, and low physical activity, was significantly higher among older adults, women, the uneducated, the unemployed, urban dwellers, and people from rich households. The study found that NCD-related lifestyle characteristics were poorly compliant with standard guidelines among many adult populations in Bangladesh. The findings can inform preventative strategies to control the overwhelming NCD burden in Bangladesh, such as the promotion of physical exercise, healthy eating, and the cessation of the use of tobacco products.
Effects of socioeconomic status in cognition of people with schizophrenia: results from a Latin American collaboration network with 1175 subjects
Authors: Czepielewski Letícia Sanguinetti , Alliende Luz Maria , Castañeda Carmen Paz , Castro Mariana , Guinjoan Salvador M. , Massuda Raffael , Berberian Arthur A. , Fonseca Ana Olivia , Gadelha Ary , Bressan Rodrigo , Crivelaro Marisa , Louzã Mario , Undurraga Juan , González-Valderrama Alfonso , Nachar Rubén , Nieto Rodrigo R. , Montes Cristian , Silva Hernan , Langer Álvaro I. , Schmidt Carlos , Mayol-Troncoso Rocío , Díaz-Zuluaga Ana M. , Valencia-Echeverry Johanna , López-Jaramillo Carlos , Solís-Vivanco Rodolfo , Reyes-Madrigal Francisco , de la Fuente-Sandoval Camilo , Crossley Nicolás A. , Gama Clarissa S. ,   ANDES Network
Published: June 2021

Background

Cognition heavily relies on social determinants and genetic background. Latin America comprises approximately 8% of the global population and faces unique challenges, many derived from specific demographic and socioeconomic variables, such as violence and inequality. While such factors have been described to influence mental health outcomes, no large-scale studies with Latin American population have been carried out. Therefore, we aim to describe the cognitive performance of a representative sample of Latin American individuals with schizophrenia and its relationship to clinical factors. Additionally, we aim to investigate how socioeconomic status (SES) relates to cognitive performance in patients and controls.

Methods

We included 1175 participants from five Latin American countries (Argentina, Brazil, Chile, Colombia, and Mexico): 864 individuals with schizophrenia and 311 unaffected subjects. All participants were part of projects that included cognitive evaluation with MATRICS Consensus Cognitive Battery and clinical assessments.

Results

Patients showed worse cognitive performance than controls across all domains. Age and diagnosis were independent predictors, indicating similar trajectories of cognitive aging for both patients and controls. The SES factors of education, parental education, and income were more related to cognition in patients than in controls. Cognition was also influenced by symptomatology.

Conclusions

Patients did not show evidence of accelerated cognitive aging; however, they were most impacted by a lower SES suggestive of deprived environment than controls. These findings highlight the vulnerability of cognitive capacity in individuals with psychosis in face of demographic and socioeconomic factors in low- and middle-income countries.
Successful management of invasive rats across a fragmented landscape
Authors: Barney Sarah K , Leopold Devin R , Francisco Kainana , Flaspohler David J , Fukami Tadashi , Giardina Christian P , Gruner Daniel S , Knowlton Jessie L , Pitt William C , Wilson Rankin Erin E
Published: June 2021

Introduced mammalian predators are responsible for the decline and extinction of many native species, with rats (genus Rattus) being among the most widespread and damaging invaders worldwide. In a naturally fragmented landscape, we demonstrate the multi-year effectiveness of snap traps in the removal of Rattus rattus and Rattus exulans from lava-surrounded forest fragments ranging in size from <0.1 to >10 ha. Relative to other studies, we observed low levels of fragment recolonization. Larger rats were the first to be trapped, with the average size of trapped rats decreasing over time. Rat removal led to distinct shifts in the foraging height and location of mongooses and mice, emphasizing the need to focus control efforts on multiple invasive species at once. Furthermore, because of a specially designed trap casing, we observed low non-target capture rates, suggesting that on Hawai‘i and similar islands lacking native rodents the risk of killing non-target species in snap traps may be lower than the application of rodenticides, which have the potential to contaminate food webs. These efforts demonstrate that targeted snap-trapping is an effective removal method for invasive rats in fragmented habitats and that, where used, monitoring of recolonization should be included as part of a comprehensive biodiversity management strategy.
The quality of research exploring in-session measures of CBT competence: a systematic review
Authors: Rayson Kathryn , Waddington Louise , Hare Dougal Julian
Published: June 2021

Background:

Cognitive behavioural therapy (CBT) is in high demand due to its strong evidence base and cost effectiveness. To ensure CBT is delivered as intended in research, training and practice, fidelity assessment is needed. Fidelity is commonly measured by assessors rating treatment sessions, using CBT competence scales (CCSs).

Aims:

The current review assessed the quality of the literature examining the measurement properties of CCSs and makes recommendations for future research, training and practice.

Method:

Medline, PsychINFO, Scopus and Web of Science databases were systematically searched to identify relevant peer-reviewed, English language studies from 1980 onwards. Relevant studies were those that were primarily examining the measurement properties of CCSs used to assess adult 1:1 CBT treatment sessions. The quality of studies was assessed using a novel tool created for this study, following which a narrative synthesis is presented.

Results:

Ten studies met inclusion criteria, most of which were assessed as being ‘fair’ methodological quality, primarily due to small sample sizes. Construct validity and responsiveness definitions were applied inconsistently in the studies, leading to confusion over what was being measured.

Conclusions:

Although CCSs are widely used, we need to pay careful attention to the quality of research exploring their measurement properties. Consistent definitions of measurement properties, consensus about adequate sample sizes and improved reporting of individual properties are required to ensure the quality of future research.
Cataclysmic Variable Stars
Authors: Warner Brian
Published: June 2021

The evolution of single stars on and away from the main sequence is well understood. A degenerate core is formed in a star as the star leaves the main sequence and expands to a giant with a radius typically 50 - 500 Ro . Observationally it is known that most stars are members of binary systems, and among these many have orbital periods less than 100 y. It can happen, therefore, that the expanding envelope of the primary of a binary system can reach to the secondary. As this happens, the primary fills its Roche tidal lobe and transfers matter to the secondary; if the primary has a radiative envelope the rate at which this occurs exceeds the Eddington limit of the secondary, which therefore repels the incoming gas, forming a common envelope around the two stars. Friction within the envelope causes the stars to spiral towards each other until the energy and angular momentum extracted from the binary orbit and transferred to the envelope are sufficient to eject the common envelope as a planetary nebula, leaving a short period binary comprising a white dwarf and a main sequence star.

This mechanism of producing short period binaries containing white dwarfs, proposed by Ostriker and by Paczynski (1976), is the probable origin of the class of objects known as Cataclysmic Variable Stars (CVs), which encompass the classical novae, dwarf novae, novalike variables and a variety of related objects. Evidence has been accumulating for forty years (Crawford & Kraft 1956, Warner 1995a) that every CV consists of a secondary star (usually a dwarf, but a few systems contain giants) filling its Roche lobe and transferring mass to a white dwarf primary. In systems of normal chemical composition the orbital periods lie between 75 mins and ~250 d, with the majority having . A few hydrogen-free systems are known for which 17 mins < Porb < 50 mins. It should be noted that CVs are very compact binary systems: for h such a binary would fit inside the Sun.
Surveys for Metal-Poor Stars in the Galaxy: A New Window on the Low-Abundance Universe
Authors: Beers T.C.
Published: June 2021

Measurement of the abundances of the light and heavy elements in stars of the Milky Way galaxy is the cornerstone for the study of numerous aspects of chemical evolution in galaxies and the Universe. We stand poised to enter an era of rapid understanding, as new-generation telescopes with apertures in the 8m-10m class enable astronomers to obtain high-resolution, high-signal-to-noise near-UV, optical, and IR spectra of the stars which have locked up the chemical history of our Galaxy in their outer atmospheres. It is thus appropriate to review present surveys for the low-metallicity stars of our Galaxy, as the stars we uncover today will be studied so intensively in the coming decades.
Chemical Evolution of Elliptical Galaxies: Mg2 Gradients and G-Dwarf Problem
Authors: Arimoto N. , Kobayashi C.
Published: June 2021

Stellar populations of elliptical galaxies were studied extensively in the recent past (eg., Arimoto & Yoshii 1987; Buzzoni et al. 1992; Worthey 1994; Kodama & Arimoto 1997). However, colours and line-strengths analysed by these approaches came mainly from central regions of galaxies and possible variations of stellar population structure within a galaxy were entirely ignored. Kodama & Arimoto (1997) recently show that a colour-magnitude (CM) relation of ellipticals in Coma cluster (Bower, Lucey, & Ellis 1992), and the CM relation of cluster ellipticals in general, should originate from a difference in mean stellar metallicities, as suggested by Arimoto & Yoshii (1987), and cannot be due to an increase of mean stellar age towards luminous galaxies as claimed by Worthey (1994). It is quite often stated that any theory of galaxy formation should explain the origin of CM relation, or in other words, the mass (luminosity) - metallicity relation of elliptical galaxies. However, one should not forget the fact that the CM relation is defined only for stars in the central regions of galaxies; it is possible that the CM relation itself is an observational artifact, since ellipticals show in general radial gradients of metallic-line strengthes, decreasing from a centre towards outer regions (eg., Faber 1977; Davies, Sadler, & Peletier 1993; Gonzalez 1993; Carollo & Danziger 1994). Indeed, Gorgas & Gonzalez (1996) found that ellipticals with larger central Mg2 indices tend to have steeper Mg2 gradient, which suggests that global metallicities of ellipticals are perphaps universal and are independent of galaxy luminosities.
Abundances in the Gaseous Galactic Halo
Authors: Sofia Ulysses J.
Published: June 2021

The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.
Elemental Abundances in Quasar Absorption Line Systems
Authors: Lu Limin , Sargent Wallace W.L. , Barlow Thomas A.
Published: June 2021

We discuss elemental abundances in quasar absorption line systems and their implications for galaxy formation and chemical evolution.
Dwarf Elliptical Galaxies in the Cena and Sculptor Groups
Authors: Jerjen H. , Freeman K.C. , Binggeli B.
Published: June 2021

Côté (1995) surveyed the nearby Centaurus A (Cen A) and Sculptor (Sci) group regions in the search for gas-rich, dwarf irregular galaxies (Irr) which are associated with these galaxy aggregates. 36 Irrs have been found and confirmed as new group members via 21cm/Hα redshifts. In finding this large number of Irrs, the question rises whether systems from the other dwarf galaxy family, the gas-poor dwarf ellipticals (dE), also exist in the two groups. So far nothing is known about dE membership but taking into account the morphology-density relation for dwarfs (Binggeli et al. 1990) a number ratio Irr/dE≈ 1 - 2 would be expected. Prompted by these “missing” dEs we started a large program to identify and study dEs in Cen A and Sci. The main scientific goals are (1) to find dE candidates and to establish group membership via velocity or distance and (2) to estimate the luminosity function (LF) of dwarf galaxies to the faintest possible luminosities. For the two groups, being respectively at a mean distance of 4.0 Mpc and 2.5 Mpc, we will be able to reach dwarf galaxies 4-5 magnitudes fainter than in the previous studies in the Virgo and Fornax clusters and the five groups Leo I, Dorado, NGC1400, NGC5044, and Antlia (Sandage et al. 1985, Ferguson &: Sandage 1990). We briefly outline here first results from the CenA group. All details about the complete survey including Scl will be presented in Jerjen et al. (1997)
The Distribution of BCDGs in Voids
Authors: Lindner Ulrich , Fricke Klaus J. , Einasto Jaan , Einasto Maret
Published: June 2021

Generally the density of the environment is important for the formation and evolution of galaxies: bright elliptical galaxies reside in the centers of galaxy clusters, whereas late type galaxies preferentially populate small groups, filaments or the outskirts of rich clusters of galaxies. Furthermore, fainter galaxies define smaller voids than bright galaxies. Our investigation of void catalogues in the Northern Local Void region shows that large voids are interlaced by systems of faint galaxies dividing them into smaller subvoids (Lindner et al., 1995). This void hierarchy is an important property of the Large Scale Structure in the nearby Universe and can help to solve problems concerning the distribution of dwarf galaxies and BCDGs.
The ISM in Nearby Dwarf Galaxies
Authors: Young L. M. , Lo K. Y.
Published: June 2021

In recent years, color-magnitude diagrams have revealed that nearby dwarf galaxies have a fascinating variety of star formation histories. The fact that the dwarfs have periods of star formation activity and inactivity raises several questions. How do the properties of the interstellar medium (ISM) in a galaxy affect its star formation rate? Are the interstellar media of dwarf galaxies similar to those in spirals? And what can we learn about dwarf galaxies’ evolution from their gas contents?
2D Chemodynamical Simulations of Low-Mass Galaxies
Authors: Hensler G. , Rieschick A.
Published: June 2021

Because of their low gravitational energy, low-mass galaxies are seriously affected by energetical processes in their interstellar medium, such as supernova explosions, or by gravitational perturbations, e.g., by neighbouring galaxies. This can reasonably explain their variety of morphological types. If the evolutionary timescales of galaxies are predominantly determined by internal processes, the multi-phase character as well as star-gas interactions and phase transitions have to be taken into account. For this purpose we have developed a numerical treatment of the dynamical behaviour of gas and stars, which also accounts for the metal dependence of some processes and which can trace the chemical evolution for different elements. This so-called chemodynamical treatment is described in detail in Theis et al. (1992) and Samland et al. (1997). It considers three stellar components and devides the gas into clouds (CM, with a mass spectrum) and a hot intercloud medium (ICM). Since the element enhancement of the interstellar medium is produced by different processes with different lifetimes of their progenitors, O, Fe, and N are used as tracer elements to represent supernovae type II (SNell), type la (SNela), and planetary nebulae (PNe) contributions. While supernovae form the ICM, PNe only attribute to the CM so that only mixing effects of both gas phases can alter abundance ratios.

Due to limited computer capacities the first chemodynamical simulations of dwarf galaxies could be performed only one-dimensionally so far (see e.g., Hensler et al. 1993, 1998). The recently developed two-dimensional chemodynamical code CoDEx (Samland 1994) was first applied to massive disk galaxies and produced models of which a particular one could represent various chemical and structural observations of the Milky Way with striking agreement (Samland et al. 1997).
Fundamental Arguments of the Current Nutation Theory: Dynamical Reference Frame
Authors: Standish E.M.
Published: June 2021

The latest JPL planetary and lunar ephemerides, DE405, are now referenced to the ICRF with an accuracy of about 1 mas. This has been accomplished mainly by fitting the ephemerides to 18 VLBI observations of the Magellan Spacecraft in orbit around Venus, 1990-1994, and to 2 VLBI observations of the Phobos Spacecraft in its approach to Mars, 1989. The orientation of DE405 is discussed in more detail elsewhere in this volume (Standish, 1997). Since all of the parameters of the inner solar system are now determined to 1 mas or better, one should be able to extract numerically the fundamental arguments of the nutation theories to the level of 1 mas.

There are two ways of extracting the ecliptic, for example, from a numerical ephemeris: 1) one computes the node and obliquity of the instantaneous ecliptic at multiple points in time and then fits these with analytic functions, or 2) one fits an analytical planetary theory to the ephemerides and then computes the node and obliquity from the theory’s parameters. This paper relates a short example using method #1 and concludes that method #2 is probably more preferable.
Relativistic Considerations for Precession and Nutation
Authors: Klioner S.A. , Soffel M.
Published: June 2021

The whole scope of problems related with the rotational motion of celestial bodies is briefly discussed. Relativistic modeling of the Earth rotation is considered from a conceptual point of view. Relativistic effects in rotational equations of motion of an extended body in general relativity are discussed. Numerical values of the effects are given.
Astronomical Effects of Current Changes in Fundamental Astrometric References
Authors: Kovalevsky J. , McCarthy D.
Published: June 2021

We present a first description of the changes in the current procedures that will have to be performed in order to take into account the adoption of the ICRS as the new reference system and new nutation-precession series. A number of choices will have to be made: they are presented in this paper.
Impact-Induced Activity of The Asteroid-Comet P/1996N2 Elst-Pizarro: Yes or No?
Authors: Boehnhardt H. , Sekanina Z. , Fiedler A. , Rauer H. , Schulz R. , Tozzi G.
Published: June 2021

P/1996 N2 Elst-Pizarro was discovered with a tail of dust in July 1996 and was thus classified as periodic comet. From the orbit point of view it belongs to the outer asteroid belt and is very likely a member of the Themis family, a group of bodies originating from an asteroid collision.

The absence of a coma and the presence of the needle-like anti-tail in August 1996 did not exclude the possibility of a sudden emission event which could have been caused by the impact of another minor body on the object. However, with the development of a normal tail between September and November 1996 it became obvious that the dust emission episode continued at least for 2 months after perihelion, a scenario that is typical for gas-driven cometary activity. However, it is still possible that a collision triggered the event.

The paper summarizes the observational pro and cons for impact-induced activity in this object, possibly the first ever detected comet-asteroid of the solar system.
Mass Extinctions, Comet Impacts, and The Galaxy
Authors: Rampino Michael R. , Stothers Richard B.
Published: June 2021

The hypothesis relating mass extinctions of life on Earth to impacts of comets whose flux is partly modulated by the dynamics of the Milky Way Galaxy contains a number of postulates that can be tested by geologic evidence and statistical analyses. In an increasing number of cases, geologic evidence for impact (widespread impact debris and/or large impact craters) is found at times of mass extinction events, and the record of dated impact craters has been found to show a significant correlation with mass extinctions. Statistical analyses suggest that mass extinction events exhibit a periodic component of about 26 to 30 Myr, and periodicities of 30± 0.5 Myr and 35 ±2 Myr have been extracted from sets of well-dated impact craters. The evidence is consistent with periodic or quasi-periodic showers of impactors, probably Oort Cloud comets, with an approximately 30-Myr cycle. The best explanation for these proposed quasi-periodic comet showers involves the Sun’s vertical oscillation through the galactic disk, which may have a similar cycle time between crossings of the galactic plane.
Entry Flashes of Cometary Fragments in Jovian Upper Atmosphere
Authors: Takeuchi S. , Hasegawa H. , Watanabe J.
Published: June 2021

Short lasting flashes, called as First Precursor (PC1), were observed by some ground-based near-infrared observations for the impacts of large-sized fragments of comet Shoemaker-Levy 9 (SL9) in July 1994. The impact detections by the spacecraft Galileo [2, 7] about 10 seconds after the PC1 detections by ground based telescopes, combined with the far-side impacts of SL9 fragments as viewed from Earth, suggest that the source of the PC1 should be located in the Jovian upper atmosphere above the limb, at which the atmospheric pressure is extremely low. Thus, an important problem on the PC1 is how does the falling cometary fragment, which is a huge meteorite, emit near-infrared in the extremely thin atmosphere. The ablation model, which is usually used for an impact bolide, can only estimate flux from the bolide in a dense atmosphere at visible wavelength. In this paper, we assume that the PC1s are thermal radiation from the fragments and attempt quantitative estimations of the PCI fluxes using a simple entry flash model.
Optical Counterpart Of ICRF: Hipparcos
Authors: Lindegren L. , Perryman M.A.C.
Published: June 2021

The Hipparcos reference frame is defined by the positions and proper motions of ~105 stars given in the Hipparcos Catalogue (ESA, 1997). It is the optical counterpart of the International Celestial Reference Frame defined by the radio positions of extragalactic sources. The linking of the Hipparcos frame to the extragalactic frame is described by Kovalevsky et al. (1997) and Kovalevsky (1997). In the present review we consider only the intrinsic properties of the Hipparcos reference frame.

A complete description of the contents of the Hipparcos Catalogue is contained in Volume 1 of ESA (1997). Recent overviews have been given by Perryman et al. (1997) and Perryman (1997). The principal astrometric data provided are the barycentric coordinates (α, δ) of the stars, the trigonometric parallaxes (π) and the proper motion components (μα* = μα cos δ, μδ). These parameters are given in the main catalogue for 117955 entries along with estimated standard errors and correlation coefficients, all data being referred to the common reference epoch To = J1991.25 on the Terrestrial Time (TT) scale. Typical ranges of the astrometric standard errors and some other characteristics of the catalogue are shown in Table 1.
The Tycho Catalogue: Extension of Optical Reference Frame
Authors: HØG E.
Published: June 2021

The Tycho Catalogue contains astrometric and photometric data for the one million brightest stars on the sky. About 900000 stars are high quality astrometric reference stars. Photometry in a blue and visual band is provided.

Two extensions of the catalogue are under way. One is the extension to one magnitude fainter stars by a second reduction of the original Tycho observations, resulting in a catalogue with a total of about three million stars. The other extension is the derivation of more accurate proper motions by means of the Astrographic Catalogue positions as first epoch. This latter work will be carried out first for the one million stars, and later for all the three million, resulting in the Tycho Reference Catalogue (TRC).
Linking the Dynamical Reference frame to the ICRF
Authors: Standish E.M.
Published: June 2021

The latest JPL planetary and lunar ephemerides, DE405, are referenced to the International Celestial Reference Frame (ICRF) with an accuracy that approaches 1 mas for the four innermost planets, the sun, and the moon. This has been accomplished mainly by 18 VLBI observations of the Magellan Spacecraft in orbit around Venus. The ephemeris of Jupiter, however, is not well-determined since the various observations are not consistent within each other. The outer four planets continue to rely almost entirely upon optical observations; their ephemeris uncertainties lie in the 100-200 mas range.
Real TIme Evolution of Evolved Stars
Authors: Percy J.R.
Published: June 2021

We briefly discuss the methods of observing stellar evolution in real time, and of interpreting these observations. Then we discuss recent results on RR Lyrae stars, Population I and II Cepheids, RV Tauri stars, and related objects.
Recent Developments in the Young Planetary Nebula HEN-1357
Authors: Bobrowsky M.
Published: June 2021

Observations over the past four decades have revealed significant changes in the spectrum of Hen-1357. Here we present HST images and spectra showing the most recent developments. In 1950, Henize saw only Hα in emission; but more recent observations by Parthasarathy et al. in 1992 showed strong forbidden lines consistent with a young planetary nebula. The spherically aberrated 1992 HST images, in which Bobrowsky first optically resolved the nebula, showed a compact nebula surrounding the central star. Nebular gas appeared most strongly concentrated in an ellipse with its major axis subtending 1".6 from NW to SE. If this ellipse is actually a circular ring viewed obliquely, then our line of sight is inclined from the symmetry axis by 5°. Above and below the ring of gas are two bubbles containing lower-density gas. At the tip of each bubble, there is a hole where the gas inside the bubbles has broken through and is now escaping. The windblown appearance is consistent with the blueshifted Si IV (1394-1403Å) and Al III (1855-1863Å) doublets observed by Parthasarathy et al. that indicated the presence of a strong stellar wind. The N V (1239-1243Å) to C IV (1548-1551Å) ratio has increased in recent years, consistent with a young nebula becoming increasingly ionized. Our recent (1996) spectra reveal additional developments that show the realtime development of this young nebula. Finally, the new HST Planetary Camera images of the nebula show detailed structure indicating a much more complex object than previously known, including the presence of a companion star 0".3 from the central star.
Semi-Empirical Determination of the Position of RRAB Stars on The H-R Diagram
Authors: Jurcsik J. , Kovács G.
Published: June 2021

In a recent series of papers, it was shown that the metallicity and the absolute V, I and K mean magnitudes of RRab stars can be accurately calculated using only their periods and the low order Fourier parameters of the V light curves. The application of these formulae in conjunction with the synthetic colours of the model atmospheres and with the theoretical pulsation periods enables us to determine all the basic physical parameters (i.e. logL, logT, logM and [Fe/H]) of any variable with an accurate light curve. As a result, we might trace evolutionary tracks on the H—R diagram by plotting the stars with the same mass and metallicity. From a present sample of nearly 300 stars, signs of differences in the evolutionary statescan be suspected but not yet proven.

The accumulation of large numbers of precise light and colour curves, onthe one hand, will further improve the empirical formulae and therefore theaccuracy of the derived parameters and, on the other hand, will increase our chances of constructing better-populated empirical evolutionary tracks.
R Coronae Borealis Stars: Long-Term Photometric & Spectroscopic Studies
Authors: Cottrell P.L. , Skuljan L. , Kilmartin P.M. , Gilmore C. , Lawson W.A.
Published: June 2021

For more than a decade we have been able to acquire and analyse a significant amount of photometric data of the highly variable R Coronae Borealis (RCB) stars. This has made been possible by a photometric service observing programme instigated at the Observatory. These photometric data have been combined with less extensive spectroscopic coverage, particularly of the decline phase of these stars. These have been supplemented by observations obtained at Mount Stromlo and Siding Spring Observatories for a radial velocity study. Significantly more spectroscopic observations are now being acquired with the development of a new medium resolution spectrograph at Mount John University Observatory.

In this poster we will present recent photometric and spectroscopic results for a number of the RCB stars in our sample. This observational and analysis work can be used to provide further insight into the nature of these stars, their likely progeny and progenitors and the processes that are involved in the formation and evolution of the obscuring dust clouds which cause the decline phase.
Properties of the Subgiants in Various Types of Eclipsing Binary Systems
Authors: Karetnikov V.G.
Published: June 2021

The radius and temperature excesses are found to be largest for the subgiant stars in DS systems and in low-mass and long-period SD systems, being the smallest for the subgiant stars in AR systems and in low-mass and short-period SD-systems. Subgiant stars in AR and in more massive SD systems exhibit even the temperature deficiency which is the largest for the primariesof the AR systems. Necessity is shown to divide the class of SD systems into several groups according to masses and orbital periods while studying their properties.
The 283-Day Periodicity in the O-C Diagram of Beta Lyrae
Authors: Kreiner J.M. , Pajdosz G.
Published: June 2021

A detailed analysis of an extensive collection of primary visual, photographic and photoelectric minima of Beta Lyrae was performed. After removing the effect of the increase in orbital period we applied the Fourier analysis to the 0-C residuals. The most prominent periodicity is 283 days with amplitude about 0.05 days. It confirms the period found in the photometric light curves of Beta Lyrae [Van Hamme, Wilson and Guinan (1995)]. The 283-d quasi-variation of the period may be explained by assymetries of the light curve near the minima caused by some instabilities in disc and/or hot spot(s) brightness.
On the Short Time Scale Evolutionary History of the Contact Binary VW Cephei
Authors: Pustylnik I.
Published: June 2021

We study the short-time evolutionary history of the well-known contact binary VW Cep. Our analysis is based partly on the numerous UBV lightcurves obtained at Tartu Observatory, IUE spectra, and samples from the published data. Special attention is given to the effects of asymmetry of the light curves. A higher degree of asymmetry outside the eclipses along with the significant displacements of the brightness maxima in respect to the elongation phase is interpreted as evidence that a considerable portion of the flaring source is concentrated close to the neck connecting the components. We discuss the nature of asymmetry in terms of possible mass exchange and the flare activity and compare the results of our model computations with the record of orbital period variations over the last 60 years.
Ground-Based Surveys For Low-Luminosity Stars
Authors: Jones Hugh R.A.
Published: June 2021

Most of what we know about the Luminosity and mass function of low-mass stars has been derived from analysis of ground-based photometric and astrometric Surveys. A major uncertainty in the Interpretation of such surveys lies in the appropriate correction for unresolved binaries and in the use of a reliable colour-magnitude relation. various new surveys are now uncovering large numbers of objects which should rapidly ameliorate these ambiguities.

The recent discovery of brown dwarfs and planets has highlighted the importance of low-luminosity stars. once we understand their spectra and colours and have statistically significant samples, it will be important to use them to reliably constrain theories of star formation and chemical evolution as well as to use them as a probe of galactic structure and to reliably ascertain their contribution to baryonic dark matter. In this brief review ishall focus on ground-based field searches. Hambly (1997) reviews the very successful searches that have recently been carried out in nearby clusters.

Until the 1970s, most work on the faint-star luminosity function was based on proper-motion searches primarily by dutch researchers, in particular Luyten (e.g. 1938, 1979). The Last 20 years have seen a switch from astrometric to photometric surveys employing plate-scanning machines or CCD cameras. Combined with substantial increases in computing power these technologies have led to the discovery of large numbers of very low-luminosity Stars.
Parallaxes Using Infrared Arrays
Authors: Brockie R.M. , Jones H.R.A. , Wells M. , Longmore A.J.
Published: June 2021

We have recently carried out an infrared parallax programme on the UKIRT conducted with a 2562 array. Our observations were made in the near-infrared K-band which is ideal for observing red stars and brown dwarf candidates and has the advantage that differential colour refraction is negligible. We find a parallax of πabs = 156.0 ±13.3 mas for the archetypal late-type M dwarf vB 10 and πabs =11.1 ± 7.5 mas for PC 0025+0447 which we conclude is too distant to be a clear case of a brown dwarf and is probably a late-type M dwarf close to the hydrogen-burning limit. Recent improvements in telescopes and instrumentation working in the infrared should enable accuracies of ~ 1 mas to be obtained for future infrared parallax programmes.
Completing the Local Sample with Tycho
Authors: Smart R.L. , Pannunzio R. , Lattanzi M.G. , Mclean B.
Published: June 2021

The Tycho Catalogue contains proper motions and low precision parallaxes with a median precisions of 25 mas, while having high precision B and V magnitudes (median precision of 0.07 and 0.06 respectivly). The number of highparallax stars is quite unexpected, with over 30 previously unreferenced, non-Hipparcos, stars with a parallax >500 mas and over 2000 with a parallax >250 mas. While many of these are probably mistakes, the completeness limit of Tycho and the precise magnitudes provide us with a way to intelligently build a complete picture of the nearby star field. Catalogues of nearby stars provide us with many fundamental parameters in the field of stellar astronomy, but the completness of known stars within say even 8pcs is still underestimated by about 30%, i.e., 50-60 systems (T.J. Henry, CSSS8, ASP Conf Series 64, 1994).

In a new program at Torino we are using the Tycho Catalogue to intelligently build a list of possible candidates for a 1Opc volume. Figure 1 shows that Tycho will contain basically all ZAMS to spectral type M3 within 10 pes, M5 to 4pcs and M6 to 2pcs. A comparison of the photometric and Tycho distances provides a list free of giants and systems where binarity has affected the color. This list is then added to the Torino Parallax program where we expect to provide more precise parallaxes.