bluuebunny/crossref_metadata_2025 huggingface dataset:
Relativistic fluid dynamics: physics for many different scales
Authors: Andersson Nils , Comer Gregory L.
Published: June 2021

The relativistic fluid is a highly successful model used to describe the dynamics of many-particle systems moving at high velocities and/or in strong gravity. It takes as input physics from microscopic scales and yields as output predictions of bulk, macroscopic motion. By inverting the process—e.g., drawing on astrophysical observations—an understanding of relativistic features can lead to insight into physics on the microscopic scale. Relativistic fluids have been used to model systems as “small” as colliding heavy ions in laboratory experiments, and as large as the Universe itself, with “intermediate” sized objects like neutron stars being considered along the way. The purpose of this review is to discuss the mathematical and theoretical physics underpinnings of the relativistic (multi-) fluid model. We focus on the variational principle approach championed by Brandon Carter and collaborators, in which a crucial element is to distinguish the momenta that are conjugate to the particle number density currents. This approach differs from the “standard” text-book derivation of the equations of motion from the divergence of the stress-energy tensor in that one explicitly obtains the relativistic Euler equation as an “integrability” condition on the relativistic vorticity. We discuss the conservation laws and the equations of motion in detail, and provide a number of (in our opinion) interesting and relevant applications of the general theory. The formalism provides a foundation for complex models, e.g., including electromagnetism, superfluidity and elasticity—all of which are relevant for state of the art neutron-star modelling.
Freely Available Virtual Reality Experiences as Tools to Support Mental Health Therapy: a Systematic Scoping Review and Consensus Based Interdisciplinary Analysis
Authors: Best Paul , Meireles Matilde , Schroeder Franziska , Montgomery Lorna , Maddock Alan , Davidson Gavin , Galway Karen , Trainor David , Campbell Anne , Van Daele Tom
Published: June 2021

The primary purpose of this article is to review the potential therapeutic value of freely available VR content as an addition to the practitioners ‘toolkit’. Research has shown that virtual reality (VR) may be useful to extend existing guided imagery-based practices found in traditional mental health therapy. However, the use of VR technology within routine mental health practice remains low, despite recent reductions in equipment costs. A systematic scoping review and interdisciplinary analysis of freely available VR experiences was performed across two popular online databases (SteamVR and Oculus.com). A total of 1785 experiences were retrieved and screened for relevance with 46 meeting the inclusion criteria. VR content was then reviewed for potential therapeutic value by an interdisciplinary panel with experience across a number of therapeutic interventions including cognitive behavioural therapy, Rogerian counselling, mindfulness-based therapies. and family therapy. Eleven (22%) of the 50 freely available VR experiences were reported to have therapeutic potential as tools to support routine mental health therapy. These included support with the following mental health issues—low mood, social anxiety, stress reduction and fear of heights. Guidance of a qualified mental health practitioner was recommended in all cases to maximise the benefit of the VR experiences retrieved. While the quality is variable, freely available VR experiences may contain valuable content that could support mental health therapy. This includes as a homework activity or as an initial setting for case formulation and behavioural experiments.
Geschichtsdidaktische Forschung und allgemeine Unterrichtsforschung: Unbekannte Verwandte?
Authors: Trautwein Ulrich , Schreiber Waltraud , Hasenbein Lisa
Published: June 2021

Dieser Beitrag beleuchtet das Verhältnis von Basisdimensionen der Unterrichtsqualität (Modell der drei Basisdimensionen sowie Syntheseframework) aus der allgemeinen Unterrichtsforschung und geschichtsdidaktischen Modellbildungen. Zu diesem Zweck arbeiten wir das Fehlen einer vertieften theoretischen und empirischen Auseinandersetzung mit Modellen der allgemeinen Unterrichtsforschung in der Geschichtsdidaktik heraus. Darauf aufbauend diskutieren wir die Stärken und Grenzen von Modellen, die eine bestimmte Zahl von Basisdimensionen der Unterrichtsqualität postulieren, stellen ein geschichtsdidaktisches Kompetenzmodell (das sogenannte FUER-Modell) vor, das eine Auseinandersetzung mit Basisdimensionen ermöglicht und zeigen auf, wie die Basisdimensionen mit geschichtsdidaktischen Vorstellungen in Einklang zu bringen sind – und wo dies nicht so einfach möglich ist.
Diagnosis of Chlamydia trachomatis genital infections in the era of genomic medicine
Authors: Shetty Seema , Kouskouti Christina , Schoen Uwe , Evangelatos Nikolaos , Vishwanath Shashidhar , Satyamoorthy Kapaettu , Kainer Franz , Brand Angela
Published: June 2021

Purpose

Chlamydial genital infections constitute significant sexually transmitted infections worldwide. The often asymptomatic status ofC. trachomatis(CT) infections leads to an increased burden on human reproductive health, especially in middle- and low-income settings. Early detection and management of these infections could play a decisive role in controlling this public health burden. The objective of this review is to provide an insight into the evolution of diagnostic methods for CT infections through the development of new molecular technologies, emphasizing on -omics’ technologies and their significance as diagnostic tools both for effective patient management and control of disease transmission.

Methods

Narrative review of the diagnostic methodologies of CT infections and the impact of the introduction of -omics’ technologies on their diagnosis by review of the literature.

Results

Various methodologies are discussed with respect to working principles, required specifications, advantages, and disadvantages. Implementing the most accurate methods in diagnosis is highlighted as the cornerstone in managing CT infections.

Conclusion

Diagnostics based on -omics’ technologies are considered to be the most pertinent modalities in CT testing when compared to other available methods. There is a need to modify these effective and accurate diagnostic tools in order to render them more available and feasible in all settings, especially aiming on turning them to rapid point-of-care tests for effective patient management and disease control.
Synchrotron X-ray microtomography and multifractal analysis for the characterization of pore structure and distribution in softwood pellet biochar
Authors: Srocke Franziska , Han Liwen , Dutilleul Pierre , Xiao Xianghui , Smith Donald L. , Mašek Ondřej
Published: June 2021

Biochar pores in the micrometer range (1–100 µm) derive from cellular structures of the plant biomass subjected to pyrolysis or can be the result of mechanical processing, such as pelleting. In this study, synchrotron X-ray microtomography was used to investigate the internal pore structure of softwood pellet biochar produced by slow pyrolysis at 550 and 700 °C. The microtomographic data sets consisted of 2025 images of 2560 × 2560 voxels with a voxel side length of 0.87 µm. The three-dimensional reconstructions revealed that pelleting and pyrolysis significantly altered the pore structures of the wood feedstock, creating a network of connected pores between fragments that resembled the wood morphology. While higher pyrolysis temperature increased the specific surface area (as determined by BET nitrogen adsorption), it did not affect the total observed porosity. Multifractal analysis was applied to assess the characteristics of the frequency distribution of pores along each of the three dimensions of reconstructed images of five softwood pellet biochar samples. The resulting singularity and Rényi spectra (generalized dimensions) indicated that the distribution of porosity had monofractal scaling behavior, was homogeneous within the analyzed volumes and consistent between replicate samples. Moreover, the pore distributions were isotropic (direction-independent), which is in strong contrast with the anisotropic pore structure of wood. As pores at the scale analyzed in this study are relevant, for example, for the supply of plant accessible water and habitable space for microorganisms, our findings combined with the ability to reproduce biochar with such pore distribution offer substantial advantages in various biochar applications.
Attachment and Sexual Functioning: Understanding the Mediating Role of Body Image Among LGB and Non-LGB Women
Authors: Gewirtz-Meydan Ateret , Mitchell Kimberly J. , Spivak-Lavi Zohar
Published: June 2021

INTRODUCTION

Despite studies showing that individuals with insecure attachment suffer from poor body image, and that poor body image is a main risk factor for sexual dysfunction, the mediating role of body image between attachment insecurities and sexual functioning has not been assessed. Moreover, differences in body self-consciousness among sexual minority women have not been examined, even though LGB individuals have been found to be more conscious of stigma and the disapproval of others.

Aim

To fill this gap, the current study examines the mediating role of body image self-consciousness between insecure attachment and sexual functioning among LGB and non-LGB women.

Methods

The study sample consisted of 1,001 women; of them, 808 defined themselves as heterosexual (80.7%), and 193 (19.3%) identified as LGB. The sample was a convenience sample of women who responded to ads on social media. Participants completed an online questionnaire (via Qualtrics) about their attachment orientation, body-image self-consciousness, and sexual functioning.

Main Outcome

Body image self-consciousness mediated the relationship between insecure attachment and sexual dysfunction among women in general and LGB women in particular.

RESULTS

Results indicated that among LGB women, the relationship between attachment and sexual functioning was fully mediated by body image self-consciousness. For non-LGB women, a full model with statistically significant direct and indirect effects was revealed. Both avoidant attachment and anxious attachment were related to body image self-consciousness which was, in turn, related to sexual functioning. A statistically significant direct path from avoidant attachment to sexual functioning was also revealed.

CONCLUSION

The study findings contribute to the literature by revealing the mediating role that body image self-consciousness plays between insecure attachment and sexual dysfunction among women in general and LGB women in particular.

Clinical Implications

This study provides support for the negative relationship between body image self-consciousness and sexual functioning of women regardless of sexual orientation, and suggests that women affected by body image concerns might be prone to more sexual dysfunction. Therefore, body image self-consciousness should be brought up in sex therapy sessions and future interventions. Clinicians should also be cognizant of differences between LGB and non-LGB women in terms of this effect, taking into account the history of stigma that LGB women may have endured and how this history affects their body image.
The Sense of Injustice and the Origin of Modern Democracy
Authors: Smith Bruce J.
Published: June 2021

A careful study of the political thought of Machiavelli, Hobbes, and Locke, revealing the roots of modern democracy.
EU Operational Powers and Legal Protection: A Legal Theory Perspective on the Operational Powers of the European Border and Coast Guard
Authors: Schotel Bas
Published: June 2021

For the first time in its history, the EU is in the process of acquiring significant and genuine permanent operational powers. A new Regulation on the European Border and Coast Guard provides Frontex with a permanent corps of 10,000 border guards—3,000 of which will be EU agents—its own equipment, and its own competences to intervene along the EU borders and beyond. The operational powers will allow the EU to directly and physically intervene in tangible reality.

This Article argues that the conferral of operational powers on the EU poses a risk to individual legal protection. This is because once authorities have acquired operational powers of a certain extent and quality, they can afford to act against or without the law by simply overpowering or eluding the legal mechanisms that normally constrain the exercise of public power. So far, Members of the European Parliament and academics critical of Frontex and the new Regulation have overlooked this issue and concentrated exclusively on how to legally constrain the exercise of operational powers. This Article addresses this blind spot by examining whether and how public law should place legal constraints not only on the exercise but also on the build-up of operational powers.
Impact on quantitative fit-test results after application of prophylactic hydrocolloid dressing under N95 respirators
Authors: Ng Irene , Kave Benjamin , Begg Fiona , Sage Sarah , Segal Reny , Williams Daryl L.
Published: June 2021

Objective:

Discomfort and device-related pressure injury (DRPI) caused by N95 filtering facepiece respirators (FFRs) are common. The use of prophylactic hydrocolloid dressings is one of the strategies that may improve comfort and reduce DRPI. In this study, we investigated the impact of these dressings on N95 respirator fit.

Methods:

We performed a repeat quantitative fit testing through the Respiratory Protection Program on 134 healthcare workers (HCWs), who applied hydrocolloid dressings on the bridge of their nose under the N95 FFRs that they passed the initial fit test with, but reported discomfort with the FFR.

Results:

With the hydrocolloid dressings in place, the fit-test pass rate for the semirigid cup style (3M 1860) was 94% (108 of 115); for the the vertical flat-fold style (BYD), the pass rate was 85% (44 of 52); for the duckbill style (BSN medical ProShield and Halyard Fluidshield), the pass rate was 81% (87 of 108); and for the 3-panel flat-fold style (3M Aura) N95 FFRs, the pass rate was 100% (3 of 3). There was a statistically significant reduction in the overall fit factors for both the vertical flat-fold and duckbill type N95 respirators after the application of hydrocolloid dressings.

Conclusions:

Hydrocolloid dressings are likely to disturb the mask seal for nonrigid-style N95 FFRs, particularly the vertical flat-fold style and the duckbill style N95 FFRs. Given the risk of mask seal disturbance of N95 respirators as shown in this study, we advocate that any HCW requiring the use of prophylactic dressings should undergo repeat quantitative fit testing with the dressing in place prior to using the dressing and mask in combination.
Couplings for determinantal point processes and their reduced Palm distributions with a view to quantifying repulsiveness
Authors: Møller Jesper , O’Reilly Eliza
Published: June 2021

For a determinantal point process (DPP) X with a kernel K whose spectrum is strictly less than one, André Goldman has established a coupling to its reduced Palm process $X^u$ at a point u with $K(u,u)>0$ so that, almost surely, $X^u$ is obtained by removing a finite number of points from X. We sharpen this result, assuming weaker conditions and establishing that $X^u$ can be obtained by removing at most one point from X, where we specify the distribution of the difference $\xi_u: = X\setminus X^u$. This is used to discuss the degree of repulsiveness in DPPs in terms of $\xi_u$, including Ginibre point processes and other specific parametric models for DPPs.
Population dynamics driven by truncated stable processes with Markovian switching
Authors: Zhang Zhenzhong , Tong Jinying , Meng Qingting , Liang You
Published: June 2021

We focus on the population dynamics driven by two classes of truncated $\alpha$-stable processes with Markovian switching. Almost necessary and sufficient conditions for the ergodicity of the proposed models are provided. Also, these results illustrate the impact on ergodicity and extinct conditions as the parameter $\alpha$ tends to 2.
On classes of life distributions based on the mean time to failure function
Authors: Khan Ruhul Ali , Bhattacharyya Dhrubasish , Mitra Murari
Published: June 2021

The performance and effectiveness of an age replacement policy can be assessed by its mean time to failure (MTTF) function. We develop shock model theory in different scenarios for classes of life distributions based on the MTTF function where the probabilities $\bar{P}_k$ of surviving the first k shocks are assumed to have discrete DMTTF, IMTTF and IDMTTF properties. The cumulative damage model of A-Hameed and Proschan [1] is studied in this context and analogous results are established. Weak convergence and moment convergence issues within the IDMTTF class of life distributions are explored. The preservation of the IDMTTF property under some basic reliability operations is also investigated. Finally we show that the intersection of IDMRL and IDMTTF classes contains the BFR family and establish results outlining the positions of various non-monotonic ageing classes in the hierarchy.
COMMUTING PROBABILITY OF COMPACT GROUPS
Authors: ABDOLLAHI ALIREZA , MALEKAN MEISAM SOLEIMANI
Published: June 2021

For any (Hausdorff) compact group G, denote by
$\mathrm{cp}(G)$
the probability that a randomly chosen pair of elements of G commute. We prove that there exists a finite group H such that
$\mathrm{cp}(G)= {\mathrm{cp}(H)}/{|G:F|^2}$
, where F is the FC-centre of G and H is isoclinic to F with
$\mathrm{cp}(F)=\mathrm{cp}(H)$
whenever
$\mathrm{cp}(G)>0$
. In addition, we prove that a compact group G with
$\mathrm{cp}(G)>\tfrac {3}{40}$
is either solvable or isomorphic to
$A_5 \times Z(G)$
, where
$A_5$
denotes the alternating group of degree five and the centre
$Z(G)$
of G contains the identity component of G.
Intelligent optimal control considering dynamic posture compensation for a cantilever roadheader
Authors: Fang Lixia , Liu Zhigang , Wu Miao
Published: June 2021

The control of dynamic spatial posture for cantilever roadheader is one of the vital problems for intelligent mining, which directly affect the forming quality of cutting tunnel. Therefore, this paper proposed an intelligent optimal combination compensation strategy to adjust the real-time dynamic posture of cantilever roadheader. First, based on the topological structure analysis of cantilever roadheader, the structural loop compensation model for spatial posture deviation was established. Afterward, the principal component analysis (PCA) and multi-objective particle swarm optimization (MPSO) algorithm were applied to improve the analysis speed and accuracy of posture deviation. Finally, parallel dynamic cooperative optimization (PDCO) strategy was combined to achieve the accurate adjusting of posture deviation. The actual experimental and application results indicate that the intelligent optimal combination compensation strategy proposed in the paper can significantly improve the accuracy of the cutting tunnel. The intelligent optimal compensation strategy proposed in this paper transforms the transient spatial posture deviation into structural loop compensation, and implements by parallel cooperative strategy, finally to realize the fast analysis and efficient implementation of spatial dynamic posture deviation for cantilever roadheader during cutting process. The work of this paper provides an effective reference for intelligent deep and remote underground mining, and it can also be applied to effective control of dynamic spatial posture for intelligent engineering machinery products.
THE INFLUENCE OF ORTHOGRAPHY ON ORAL VOCABULARY ACQUISITION IN LEARNERS OF CHINESE AS A SECOND LANGUAGE
Authors: Zhang Jie , Li Hong , Liu Yang
Published: June 2021

The present study investigated the effects of exposure to Chinese orthography on learning phonological forms of new words in learners of Chinese as a second language. A total of 30 adult learners of Chinese studied spoken label and picture associations presented either with phonologically accurate characters, characters with partial phonological information, or no orthography. Half the phonologically accurate or partially accurate characters were semantically transparent or opaque. Spoken labels were recalled without orthography presence. Results showed that exposure to phonologically accurate and semantically transparent characters during learning did not enhance the recall of the spoken labels compared to no orthography. But exposure to characters with partial phonological information and semantically opaque characters significantly hindered vocabulary learning. The implications for Chinese as a second language vocabulary acquisition and instruction are discussed.
The effect of conservation policies on wildlife hunting and consumption in north-eastern Madagascar
Authors: Randriamady Hervet J , Park Seollee , Andrianarimanana Danamona , Berobia Abdy , Golden Christopher D
Published: June 2021

The Makira Natural Park (Makira) is the largest terrestrial protected area in Madagascar, supporting nearly 200,000 people living around the park, who derive a significant proportion of their animal-source foods from hunting. Makira is currently managed with three different policies: (1) traditional management with no external assistance; (2) community-based forest management (Gestion Contractualisée des Forêts; GCF) with non-governmental support and externally developed policies; and (3) strict external management policies (Zone d’Occupation Controlée; ZOC), meaning a zone of controlled residence for communities inside the core protected area. Here, we longitudinally assess the impacts of these policies on wildlife hunting and consumption by using a difference-in-differences method to evaluate policy efficacy. We found that externally developed conservation policies led to drastically reduced wildlife hunting and consumption in Makira. We also found that public education in the form of environmental awareness-raising, conducted 1 year before adoption, led to a greater concealment of hunting behaviours. Overall, wildlife hunting and consumption have decreased in the Makira region since the adoption of GCF and ZOC policies and could be effective at reducing the unsustainable wildlife hunting across the Makira, particularly when supported by economic development and the creation of alternative sources of livelihood and food.
Paternal hypoxia exposure impairs fertilization process and preimplantation embryo development
Authors: Tao Hai-Ping , Jia Gong-Xue , Zhang Xiao-Na , Wang Yu-Jun , Li Bin-Ye , Yang Qi-En
Published: June 2021

Environmental hypoxia exposure causes fertility problems in human and animals. Compelling evidence suggests that chronic hypoxia impairs spermatogenesis and reduces sperm motility. However, it is unclear whether paternal hypoxic exposure affects fertilization and early embryo development. In the present study, we exposed male mice to high altitude (3200 m above sea level) for 7 or 60 days to evaluate the effects of hypoxia on sperm quality, zygotic DNA methylation and blastocyst formation. Compared with age-matched controls, hypoxia-treated males exhibited reduced fertility after mating with normoxic females as a result of defects in sperm motility and function. Results ofin vitrofertilization (IVF) experiments revealed that 60 days’ exposure significantly reduced cleavage and blastocyst rates by 30% and 70%, respectively. Immunohistochemical staining of pronuclear formation indicated that the pronuclear formation process was disturbed and expression of imprinted genes was reduced in early embryos after paternal hypoxia. Overall, the findings of this study suggested that exposing male mice to hypoxia impaired sperm function and affected key events during early embryo development in mammals.
The Most Metal-Rich Dwarf Stars in the Galactic Disk
Authors: Feltzing Sofia
Published: June 2021

The metal-rich dwarf stars in the solar neighbourhood have historically not attracted as much attention as the metal-poor (halo) stars which tell us about the early phases of the chemical evolution of our galaxy. The properties of metal-rich stars are highly important when we try to interpret integrated spectra from metal-rich stellar populations, such as the Bulge and elliptical galaxies. A small group of so called super metal rich stars (SMR) have played a significant role in shaping the conceptions of such populations. Famous examples are the dwarf HR1614 and the giant μ Leonis. In the review by Taylor (1996) SMR stars are discussed in great detail, in particular the reality of extremly high [Fe/H]. Taylor (1996) find that no giant stars fulfil the criteria fulr SMR-ness that he sets and only a handful of dwarf stars do, and most of them are possible candidates rather than firm detections.

A few recent studies have studied known SMR candidates and stars with high [M/H] (as derived from photometry), Feltzing & Gustafsson (1997), Castro et al. (1997), Gonzalez (1997), McWilliam & Rich (1994), Castro et al. (1996). A first conclusion is that there are indeed quite a few stars with [Fe/H] > 0.2 dex (the definition of SMR, see Taylor 1996). We will here review these studies in some detail.

The combination of abundance ratios with kinematical data can detail the picture even further. For example we can study stars on highly eccentric orbits which trace the evolution in the galactic disk closer to the galctic centre. Not much is known about these stars but we did have some very intriguing observations; Barbuy & Grenon (1990) (hereafter BG90) found that dwarf stars on very eccentric orbits contained much more oxygen than what was expected from standard models of galactic chemical evolution of the disk, Edvardsson et al.(1993) (hereafter E93) found large spreads and “upturns” for certain elements, Na, Si, Ti, Al, for stars with 0.0dex < [Fe/H] < 0.2 dex.
The Low-Mass Stellar Luminosity Function of the 30 Dor Starburst Cluster
Authors: Zinnecker Hans
Published: June 2021

Diffraction limited near-infrared H-band (1.6 μm) NICMOS HST images are scheduled to be obtained in mid-October 1997 of the young cluster NGC 2070 (age 3.5 Myr) in the 30 Dor giant HII region in the LMC. The aim is to search for the low-mass (M < 2 Mʘ) low-luminosity, red pre-Main Sequence stellar population and to establish the H-band infrared luminosity function. With the NICMOS we can now determine whether the IMF in this prototypical extragalactic starburst cluster is deficient in subsolar low-mass stars or not. The best ground-based data can sample only M > 2 Mʘ. In principle, NICMOS in the H-band (F160W) is sensitive enough to reach a magnitude of ~ 23.5 in a relatively short integration time, which indeed corresponds to the fantastic possibility to detect young stellar objects with masses near the hydrogen burning limit (M=0.1 Mʘ) according to pre-Main Sequence evolutionary models. Even if we could reach only H = 22.5 (i.e. M=0.4 Mʘ), our observations will still go a long way in directly answering, by star counts, whether the IMF in starburst galaxies is low-mass deficient or not, with all the corresponding far-reaching implications.

The observations would also tell us whether the 30 Dor cluster can be regarded as a prototype young globular cluster. This possibility would be ruled out, if we found NGC 2070 to be low-mass deficient, because old globular clusters do have a rich population of low-mass stars.
Observational and Theoretical Modeling of Nutation
Authors: Mathews P.M. , Herring T.A.
Published: June 2021

The IERS nutation series was developed as a nutation series which would match observations and could be used with geodetic systems which have sensitivity to nutations but are not able to determine accurately corrections to the IAU-1980 nutation series. After experimentation with different methods for parameterizing the nutation estimation problem, the best fit to the VLBI observed nutation angle data was found by estimating selected coefficients in the Mathewset al.(1991a) nutation response function (see equation (1) below), along with other parameters to be discussed below. The estimation of the response function coefficients was also found to account for mantle anelasticity and the loading part of the ocean tide correction and therefore no corrections were applied for these effects. Their contributions should be absorbed into the estimated response coefficients. These initial analyses also showed: setting the inner-core response to zero yielded better fits to the nutation angle data than the Mathewset al.(1991b) theoretical response and resonance frequency; the amplitude of the RFCN free mode appeared to be time dependent; and the prograde annual nutation was significantly affected by the SI thermal tide which is not proportional to the S1gravitational potential.

The data set used to estimate the IERS conventions series was the GSFC nutation angle data set with 2040 pairs of adjustments to the IAU 1980 nutations in obliquity and longitude spanning the interval between 1979 and 1995. Here we also compare the IERS conventions series with a US Naval Observatory analysis of VLBI data between 1979 and August 1997. This data set consists of 2152 pairs of nutation angle estimates and extends by 1.8 years the interval covered by the GSFC data set. It also contains less pre-1984 data than the GSFC data set which accounts for the smaller increase in total number of observations than would be expected for the additional time interval covered.
An Update on The Problem of Small Comets
Authors: Brandt J.C. , A’Hearn M.F.
Published: June 2021

The evidence for a major population of small comets (SCs) is summarized in two steps. First, we briefly summarize our previous work. Second, we describe recent work that continues to find SCs. When new capabilities become available that can detect SCs, we expect to find them and this is occurring. At present, their detection is a haphazard process and we advocate a dedicated, optimized search program.

We define SCs as those icy bodies (i.e., sublimating bodies) with radius less than 1000 meters. Often the existence of SCs is inferred from effects ascribed to them. These “effects” include: lunar cratering; cratering on Ganymede; excess interplanetary hydrogen; delivery of volatile materials to the terrestrial planets; and a source of fragile bodies entering the Earth’s atmosphere. While some of these indirect methods support the existence of SCs, direct observations are clearly preferred.
The Progress of The Reference Frame
Authors: Morrison L.V.
Published: June 2021

F.W. Argelander proposed to a meeting of the Astronomischen Gessellschaft in 1867 that an accurate catalogue of all stars down to 9th magnitude should be compiled. The sky was divided into zones of declination and observations were undertaken with transit circles at a number of observatories in an international collaboration. The importance of fitting these zonal observations to one global reference frame was realized, and for this purpose A. Auwers produced a Fundamental Catalog (FC) for the Northern and Southern hemispheres in 1879 and 1883, respectively. The accuracy of the positions was about half of an arcsecond. This was the first international celestial reference frame.

This reference frame was improved over the next hundred years by continued international cooperation which was later coordinated through the IAU. These efforts culminated in the FK5 which was issued in 1988. The progress in accuracy from the FC to the FK5 is shown in Figure 1. Meanwhile, radio astronomy through the technique of Very Long Baseline Interferometry (VLBI) began to produce positions of extragalactic sources with an accuracy of a milliarcsecond (mas), which is almost two orders of magnitude better than that of the optical positions of the stars in the FK5.
Formation of The International Celestial Reference Frame
Authors: Ma C. , Arias E.F. , Eubanks T.M. , Fey A.L. , Gontier A.-M. , Jacobs C.S. , Sovers O.J.
Published: June 2021

The goal of the work described here is to create the definitive catalogue for the new International Celestial Reference Frame (ICRF) using the best data and methods available at the time the work was done. This work is the joint cooperative effort of a subgroup of the IAU Working Group on Reference Frames which was formed expressly for this purpose in February 1995. The authors of this report constituted the subgroup. A fuller account of this report can be found in the introduction to the ICRF catalog (IERS 1997).

The ICRF of 608 sources presented here is based on essentially all the VLBI observations accu-mulated over about 15 years in several worldwide programs. Dual frequency Mark III data have both geodetic and astrometric applications. Most of the data (95% of nearly 2 million observations) were acquired primarily for geodetic purposes. The major geodetic programs include: NASA’s Crustal Dynamics Project/Space Geodesy Program and USNO’s NAVEX sessions for the terrestrial reference frame, as well as IRIS, NAVNET and NEOS sessions for monitoring Earth rotation. The geodetic programs have used the brightest radio sources, gradually concentrating on the most com-pact as sensitivity improved. These geodetic sources were also the foundation of astrometric work because of the large number of observations for the ~150 most commonly used. The astrometric programs which densify the sky include the Radio-Optical Reference Frame sessions done by US Naval Research Laboratory (NRL) and USNO and the space navigation efforts of Jet Propulsion Laboratory (JPL).
Placing Schmidt Astrometry on The ICRS
Authors: Bucciarelli B. , Lattanzi M.G. , Lasker B.M.
Published: June 2021

The sky-limited, large-area photographic surveys which are being used for the construction of the second generation Guide Star Catalog (GSC-II) will be for many years to come the largest astronomical database available. The survey plates are typically placed on a 5-degree grid, with each plate area of about 42 square degrees, for a total of more than 1700 plates covering the whole sky. The expected data volume is about 2 Tbytes per bandpass. The final product will consist of an all-sky catalog of positions, proper motions, magnitudes and at least one color to a minimum of V=18. Among the scientific motivations behind such an endeavor let us mention operation of ground-based telescopes and future space missions, observation planning, statistical investigations (see, e.g., Lasker et al. 1995, Cannon 1997)
Link of the Hipparcos Catalogue to the ICRS
Authors: Kovalevsky J.
Published: June 2021

In compliance with the 1991 IAU resolutions on reference frames, the merged Hipparcos Catalogue had to be aligned in such a way that it represents at optical wavelengths the International Celestial Reference System (ICRS). This was realized as a combination of particular solutions obtained from observations of radio stars by radio interferometry, observation of quasars relative to Hipparcos stars, photographic plates including galaxies and Hipparcos stars, star catalogues referred to extragalactic objects, HST observations, and comparison of Earth orientation parameters obtained by VLBI and ground-based optical observations reduced with Hipparcos positions and proper motions. The individual results generally agree within 10 mas in orientation at epoch and 1 mas/yr in spin of the system. Two methods were used to combine the results and yielded uncertainties of 0.6 mas in orientation and 0.25 mas/yr in spin.
Linking the FK5 to the ICRF
Authors: Mignard F. , Froeschile M.
Published: June 2021

The Hipparcos optical reference frame is compared to the basic FK5 in order to determine the orientation at T0 = 1991.25 and the global spin between the two frames. The components of the spin are significant and suggest a correction the IAU76 value of the precession constant and to a possible non-precessional motion of the equinox of the FK5. The regional errors are analysed with harmonic functions and found to be as large as 150 mas in position and 3 mas/yr in proper motion.
Joint Discussion 8: Stellar Evolution in Real Time, Part I Explicit Evidences for Stellar Evolution
Authors: Guinan E.F. , Koch R.H.
Published: June 2021

JD8 assembled for half-day sessions on August 22 & 23, 1997 in a satisfactory meeting hall. Between 350 and 400 delegates - about 50% larger than anticipated - attended most of the sessions.

The theme of the meeting developed from initial conversations between R. H. Koch and Y. Kondo and was extended by E. F. Guinan. Opinions from the officers of Commissions 27 and 42 were favorable to seeking IAU approval and eventually the co-sponsoring Commissions came on board.

In essence, all the organizing workers recognized that there did not exist a broad recognition that we really do know specific stars whose evolution we have actually perceived and that there are also statistical interpretations (not the conventional isochrones in an HRD or CMD) for ensembles of stars which lead to the same conclusion.

The presentation compiled here is really a distillation of short offerings from the JD participants provided against a deadline which was regrettably close at hand. A full presentation of the meeting Proceedings will appear in The New Astronomy series of Elsevier. E. R. Jewell prepared the final files.
Watching Stars Evolve: Rapid Evolutionary Changes of the Post-AGB Star - FG SGE
Authors: Guinan E.F. , Efimov Yu. S. , Margheim S.J.
Published: June 2021

The variable post-AGB star FG Sge has provided an unique opportunity to study phenomenon which may be characteristic of the post-PN stage of stellar evolution. FG Sge is the central star in the 36-arcsec PN He 1-5 that over the last 50 yrs has been undergoing rapid evolutionary changes. Most notable are changes in temperature, luminosity, chemical composition and pulsation period. Starting in mid-1992, the star has undergone several large dimming events from which it has yet to recover. These events closely resemble the dimming events commonly observed in R CrB stars which result from dust formation in ejected envelopes. From all the evidence, it now appears that FG Sge has evolved into a R CrB star.

In this paper we first summarize the recent photometric history of the FG Sge from UBVRI photometry obtained during 1990-1997. We then combine these data with earlier photometry to define the star’s light bevavior over the last 100 yrs. The photometry is also combined with available spectroscopic polarimetric, and IR observations. Particlar attention is given to comparing FG Sge’s post-dimming behavior with contemporaneous observations of R CrB itself, also done on the same photometric system.
A Study of the Young Star V1331 CYG in a Compact Star-Forming Region
Authors: Hojaev Alisher , Zheleznyak Alexander
Published: June 2021

The peculiar T Tauri type star V1331 Cyg = LkH 120, located in the dark cloud Lynds 984, is a FU Orionis pre-outburst candidate (McMuldroch et al., 1993). This star embedded in circumstellar bright nebulosity is also surrounded by a helix-shaped nebula originated from the star. We obtained a series of speckle images of V1331 Cyg on the standard VBR system on July 18-20, 1994 using the Zeiss 1000 1.0 m telescope of the High Altitude Maydanak Observatory in Uzbekistan. We also used the results of Johnson’s system photometry of V1331 Cyg, made simultaneously at Maydanak Observatory with a 0.6 m reflector. Images were computer processed. Surface photometry of the star and surrounding nebula was made and isophotes were constructed. Fourier analysis of light curves for V1331 Cyg has shown 36.2 day periodic process (Melnikov, priv. comm.) which could be due to the presence of a circumstellar disk. Morphologic analysis revealed a complex fine structure of nebula, consisting of many bright knots and obviously show a jet-like outflow. According to spectral observations (Chavarria K. 1981; Penston & Keavey 1977) the line profiles of V1331 Cyg are P Cyg type only; there are no detections of anti-P Cyg profiles during the last 25 years observations. This indicates a stable mass loss (on average, 10−7M⊙/yr) with mean velocities about −410 km/s.
Mode and Period Changes in Pulsating Stars near the main Sequence: δ Scuti Stars
Authors: Breger M.
Published: June 2021

Reported mode changes in δ Scuti stars cna usually be explained by insufficient data to obtain multiperiodic solutions and by the effect of time-variable amplitudes. The extensive data on 4 CVn obtained by the Delta Scuti network are used to illustrate that the large changes in the appearance of the power spectra in the years from 1966 to 1996 can be ascribed to amplitude variability.

The period changes of δ Scuti stars have been collected or redetermined from the available observations and are compared with values computed from evolutionary models. For the radial pulsators of Pop.I, the observations indicate (l/P)dP/dt values around 10−7 year−1 with equal distribution between period increases and decreases. The evolutionary models, on the other hand, predict that the vast majority should show increasing periods a factor of about 10 smaller than observed. Arguments are given why the rate of evolution for these relatively unevolved stars cannot yet be deduced from the observed period changes.
Angular Momentum Loss and Transfer in Close Binaries: Effects on a Human Time-Scale?
Authors: Maceroni C.
Published: June 2021

The orbital periods of binaries are known to great accuracy, their changes produce an easily detectable cumulative effect and many systems have been observed for more than a century. In tidually locked late-type binaries the orbital period changes are often related to structural or evolutionary changes. The study of the orbital period secular evolution can therefore provide information on phenomena taking place on timescales very short when compared to the typical stellar evolutionary scales, but still much longer thant the human lifetime. This paper focuses on the dynamical evolution due to magnetic braking in late-type close binaries and on the detectability of angular momentum transfer among the stellar layers.
Sakurai’s Object: Constraints from its Variability?
Authors: Gautschy T. , Duerbeck H.W. , Van Genderen A.M. , Benetti S.
Published: June 2021

The peculiar outburst of the star baptized Sakurai’s Object (SO) is a conceivable example of a late He shell flash in a post-AGB object. The new source of nuclear energy forces such objects toward high luminosities and eventually low effective temperatures; they cross the HR diagram in a comparable fashion as FG Sge did in the past - i.e., they move noticeably on the HR diagram on human timescales. From monitoring campaigns of SO during the last year, first estimates of its cooling rate were derived and in particular cyclic light variability was established. We present first results from attempts to model stellar envelopes appropriate for SO. As we hypothesize the light variability to be attributable to stellar pulsations, we aim at constraining the basic stellar parameters based on stability analyses of our envelope models. Radial, nonadiabatic stability computations provided predictions of the modal content which should be observable as SO evolves. The particular components in such mode spectra of SO as they are to appear in the coming years should indeed help to constrain basic stellar parameters such as mass and luminosity.
Rapid Evolutionary Changes in the WR Binary HD 5980
Authors: Niemela V.S. , Barbá R.H. , Morrell N.I.
Published: June 2021

Observations of the Wolf-Rayet eclipsing binary HD 5980 in the Small Magellanic Cloud show how one component of this binary system unexpectedly underwent an eruption transforming its spectral type from a hot WNE to a cooler and luminous WN11 type. Radial velocity analysis of the preoutburst spectra indicates that both components of the binary are massive stars of WN type. The component that erupted is found to be the more massive one. Differential analysis of the H Balmer and Heɪɪ Pickering emission line strengths indicates that the hydrogen content changes with the cooling of the spectrum. The maximum light of the eruption of HD 5980 had a duration of a few months, but the slow change from a WNE spectrum to WNL type took about 10 years. The present spectrum of HD 5980 is described. The environment and orbital parameters of this massive binary suggest that the lower metal content of the Small Magellanic Cloud changes the spectral appearance of WR type stars, as compared with their galactic counterparts.
The Period Changes of YY Eridani
Authors: Kim C.-H. , Jeong J.H. , Demircan O. , Muyesseroulu Z. , Budding E.
Published: June 2021

A total of eighteen times of minimum lights for YY Eri were determined from relatively new or unpublished photoelectric observations collected from Korea and Turkey. All minima available to us were intensively analyzed to deduce the character of period variation of YY Eri. It is either formed by a sinusoidal variation superimposed on an upward parabola, or a set of abrupt changes. The abrupt changes appeared to have alternatively occured in the pattern of two increases following one decrease, which may be an indication of sinusoidal variations rather than real sudden changes of period. Upward parabolic variation can be due to a secular period increase caused by mass transfer from less massive to more massive component. The sinusoidal character can arise from a third body or from a strong magnetic activity cycle. Long term sinusoidal light level variation in the light curves supports the cyclic magnetic activity effect on the orbital period. However, the third body hypothesis can not be ruled out by the present data.
V392 Orionis: Observations and Evolutionary State of a Low-Mass System
Authors: Narusawa S. , Yamasaki A. , Nakamura Y.
Published: June 2021

Although the evolution of binary systems has been qualitatively interpreted with the evolutionary scenario, the quantitative interpretation of any observed system is still unsatisfactory due to the difficulty of the quantitative treatment of mass and angular momentum transfer/loss. To reach a true understanding of the evolution of binary systems, we have to accumulate more observational evidence. So far, we have observed several binaries that are short-period and noncontact, and found the existence of extremely small-mass systems. In the present paper, we study another short-period (P=0.659d), noncontact, eclipsing binary system, V392 Ori. We have made photometric and spectroscopic observations of V392 Ori. The light curves are found to vary, suggesting the existence of circumstellar matter around the system. Combining the photometric and spectroscopic results, we obtain parameters describing the system; we find the mass of the primary component is only 0.6Mʘ- undermassive for its spectral and luminosity class A5V, suggesting that a considerable amount of its original mass has been lost from the system during the course of evolution. The low-mass problem is very important for investigation of the evolution of close binary systems: largemass loss within and/or after the main-sequence will have a significant influence on the future evolution of binary systems.
Winds And Mass-Loss From Evolved, Low-Gravity Cool Stars
Authors: Carpenter K.G. , Robinson R.D.
Published: June 2021

The character of the winds and the amount of mass-loss from stars during the red giant and supergiant stage of evolution are critical to the progression of that evolution. We therefore summarize here the results of a series of programs utilizing the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) to study the winds and mass-loss from the surface of evolved, low-gravity cool stars. We discuss the structure of the chromospheres in which the base of these stellar winds lie, the velocity of the wind and its acceleration with height, and what these spectra tell us about the mass-loss from these stars. Because of its relevance to this Joint Discussion, we will also discuss in some detail what we have learned about real-time variability of these phenomena and the implied somewhat erratic nature of the mass-loss process in at least some of these stars.