scholarly journals Invited Review: Cepheid Variables as Extra-Galactic Distance Indicators

1985 ◽  
Vol 82 ◽  
pp. 166-198 ◽  
Author(s):  
Barry F. Madore
Keyword(s):  
Local Group ◽  
Distance Scale ◽  
Published Data ◽  
Infrared Observations ◽  
Cepheid Variables ◽  
Nearby Galaxies ◽  
Distance Indicators ◽  
Convenient Access

SummaryThe role of cepheid variables in establishing the inner distance scale to nearby galaxies is discussed. Emphasis is placed on the necessity for broad wavelength coverage in attempting to account for metalliclty differences and reddening internal to the parent galaxies. In addition linear detectors are essential in minimizing the effects of any unresolved background contibution to the photometry. Recent infrared observations of Cepheids in Local Group galaxies are surveyed and all published data on extragalactic Cepheids are presented for convenient access.

scholarly journals Nonlinear Convective Pulsation Models of Second Overtone SMC Cepheids

2002 ◽  
Vol 185 ◽  
pp. 420-423
Author(s):  
M. Marconi ◽  
G. Bono ◽  
F. Caputo
Keyword(s):  
Short Distance ◽  
Selection Criteria ◽  
Distance Scale ◽  
Model Predictions ◽  
Distance Indicators

AbstractNonlinear convective pulsation models representative of SMC Cepheids pulsating in the second overtone mode are presented. Model predictions are compared with observations and implications are derived for second overtone selection criteria. The role of overtone Cepheids as distance indicators is finally investigated and the derived distance scale is at odds with the so called short distance scale.

scholarly journals DIRECT Distances to Local Group Galaxies

2000 ◽  
Vol 176 ◽  
pp. 182-186 ◽  
Author(s):  
Dimitar D. Sasselov
Keyword(s):  
Local Group ◽  
Variable Stars ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Stepping Stones ◽  
The Past ◽  
Cepheid Variables ◽  
Direct Distance ◽  
Nearby Galaxies

AbstractThe two nearby galaxies, M31 and M33, are stepping stones for most of our current efforts to understand the evolving universe at large scales. We are undertaking a long term project, called DIRECT, to improve the direct distance estimate to M31 and M33. The massive photometry we have obtained as part of our project over the past 3 years provides us with very good light curves for known and new Cepheid variables, a large number of eclipsing binaries and other variable stars.

scholarly journals The Tip of the Red Giant Branch as a Population II Distance Indicator

1999 ◽  
Vol 183 ◽  
pp. 48-53 ◽  
Author(s):  
Shoko Sakai
Keyword(s):  
Type Systems ◽  
Variable Stars ◽  
Distance Scale ◽  
Late Type ◽  
Major Disadvantage ◽  
Nearby Galaxies ◽  
Distance Indicator ◽  
Red Giant ◽  
Extragalactic Distance Scale ◽  
Distance Indicators

The period–luminosity (PL) relation of the Cepheid variable stars is the most reliable primary distance indicator for nearby galaxies, and serves as the foundation of the extragalactic distance scale, providing the firm calibration for various secondary distance indicators. However, a major disadvantage of the Cepheid distance scale is that it can only be applied to late–type systems with recent or current star formation. An alternative distance indicator is a Pop II, tip of the red giant branch (TRGB) method, which is extremely attractive because of its applicability to all morphological types of galaxies. As long as a metal–poor RGB stars are present in abundant numbers, the distance can be estimated with an accuracy that is as good as that of the Cepheid PL relation.

scholarly journals Pulsating Variable Stars in Local Group Dwarf Galaxies

2000 ◽  
Vol 176 ◽  
pp. 187-192
Author(s):  
Mario Mateo
Keyword(s):  
Local Group ◽  
Dwarf Galaxies ◽  
Current Knowledge ◽  
Physical Nature ◽  
Variable Stars ◽  
Group I ◽  
Pulsating Variable Stars ◽  
Nearby Galaxies ◽  
Observational Techniques ◽  
Distance Indicators

AbstractPulsating variables stars have had a long and prominent history in helping to map out the local Universe. Current observational techniques now make it possible to identify examples of all non-degenerate radial pulsating variables throughout much of the Local Group. I review our current knowledge of such variables in the dwarf galaxies of the Local Group. This summary tries to highlight some recent results that help underscore the use of these stars as important tools to study the physical nature of their parent galaxies as well as their continued use as important distance indicators of nearby galaxies.

scholarly journals The Distances to Nearby Galaxies from Near-Infrared Photometry of Cepheids

1985 ◽  
Vol 82 ◽  
pp. 228-231
Author(s):  
Christopher W. McAlary ◽  
Douglas L. Welch
Keyword(s):  
Near Infrared ◽  
Local Group ◽  
Infrared Photometry ◽  
Dust Extinction ◽  
Cepheid Variables ◽  
Nearby Galaxies ◽  
Ngc 6822 ◽  
Group Galaxy

AbstractNear-infrared photometry of Cepheid variables in the Local Group galaxies, NGC 6822, IC 1613, and M33, and in the M81 Group galaxy, NGC 2403 has been used to determine new, independent distances to these objects, which are almost unaffected by dust extinction and by differences in metallicities among the galaxies.

scholarly journals Eclipsing Binaries: Tools for Calibrating the Extragalactic Distance Scale

2006 ◽  
Vol 2 (S240) ◽  
pp. 79-87 ◽  
Author(s):  
Alceste Z. Bonanos
Keyword(s):  
Local Group ◽  
Hubble Constant ◽  
Magellanic Clouds ◽  
Distance Scale ◽  
Eclipsing Binaries ◽  
Fundamental Parameters ◽  
Andromeda Galaxy ◽  
Formation And Evolution ◽  
Extragalactic Distance Scale ◽  
Distance Indicators

AbstractIn the last decade, over 7000 eclipsing binaries have been discovered in the Local Group through various variability surveys. Measuring fundamental parameters of these eclipsing binaries has become feasible with 8 meter class telescopes, making it possible to use eclipsing binaries as distance indicators. Distances with eclipsing binaries provide an independent method for calibrating the extragalactic distance scale and thus determining the Hubble constant. This method has been used for determining distances to eclipsing binaries in the Magellanic Clouds and the Andromeda Galaxy and most recently to a detached eclipsing binary in the Triangulum Galaxy by the DIRECT Project. The increasing number of eclipsing binaries found by microlensing and variability surveys also provide a rich database for advancing our understanding of star formation and evolution.

Geometric Factor in Skeletal Reactions of 2-Methylpentane on Stepped Surfaces of Platinum Catalyst

1992 ◽  
Vol 57 (10) ◽  
pp. 2012-2020
Author(s):  
Vladimír Hejtmánek
Keyword(s):  
Active Sites ◽  
Platinum Catalyst ◽  
Point Of View ◽  
Geometric Factor ◽  
Published Data ◽  
Stepped Surfaces ◽  
Geometric Conditions ◽  
Surface Intermediates ◽  
Isomerization Mechanism

The role of geometric factor in the course of skeletal reactions (isomerization, hydrogenolysis) of 2-methylpentane on stepped (119), (557) and reconstructed R(557) surfaces of single crystals of platinum was evaluated with computer designed models. These calculations were compared with reported experimental data. It was found by analysis of geometric conditions that there are accessible active ensembles on double step of the reconstructed R(557) surface. In addition, these active sites are unsaturated in their coordination sphere and thus catalytically effective. This finding is consistent with published data, confirming higher catalytic activity of this surface. The various pathways of Bond Shift isomerization mechanism of 2-methylpentane from the point of view of steric demands of surface intermediates on differently located ensembles are discussed, too.

scholarly journals Overview on the Different Patterns of Tumor Vascularization

Cells ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 639
Author(s):  
Domenico Ribatti ◽  
Francesco Pezzella
Keyword(s):  
Vasculogenic Mimicry ◽  
Endothelial Cell Proliferation ◽  
Published Data ◽  
Alternative Mechanism ◽  
Tumor Vascularization ◽  
Angiogenic Therapy ◽  
Physiological Processes ◽  
Inhibition Of Angiogenesis ◽  
Therapeutic Development

Angiogenesis is a crucial event in the physiological processes of embryogenesis and wound healing. During malignant transformation, dysregulation of angiogenesis leads to the formation of a vascular network of tumor-associated capillaries promoting survival and proliferation of the tumor cells. Starting with the hypothesis formulated by Judah Folkman that tumor growth is angiogenesis-dependent, this area of research has a solid scientific foundation and inhibition of angiogenesis is a major area of therapeutic development for the treatment of cancer. Over this period numerous authors published data of vascularization of tumors, which attributed the cause of neo-vascularization to various factors including inflammation, release of angiogenic cytokines, vasodilatation, and increased tumor metabolism. More recently, it has been demonstrated that tumor vasculature is not necessarily derived by endothelial cell proliferation and sprouting of new capillaries, but alternative vascularization mechanisms have been described, namely vascular co-option and vasculogenic mimicry. In this article, we have analyzed the mechanisms involved in tumor vascularization in association with classical angiogenesis, including post-natal vasculogenesis, intussusceptive microvascular growth, vascular co-option, and vasculogenic mimicry. We have also discussed the role of these alternative mechanism in resistance to anti-angiogenic therapy and potential therapeutic approaches to overcome resistance.

The Need for Consensus About Liver Transplantation For Patients With Neuropsychiatric Wilson’s Disease

2021 ◽  
pp. 152692482110028
Author(s):  
Alberto Ferrarese ◽  
Patrizia Burra
Keyword(s):  
Liver Transplantation ◽  
Patient Outcomes ◽  
Wilson’S Disease ◽  
Therapeutic Option ◽  
Copper Metabolism ◽  
Wilson's Disease ◽  
Published Data ◽  
Neurological Improvement ◽  
Effective Therapeutic Option

Liver transplantation is considered an effective therapeutic option for Wilson’s disease (WD) patients with hepatic phenotype, since it removes the inherited defects of copper metabolism, and is associated with excellent graft and patient outcomes. The role of liver transplantation in WD patients with mixed hepatic and neuropsychiatric phenotype has remained controversial over time, mainly because of high post-operative complications, reduced survival and a variable, unpredictable rate of neurological improvement. This article critically discusses the recently published data in this field, focussing in more detail on isolated neuropsychiatric phenotype as a potential indication for liver transplantation in WD patients.

scholarly journals Novel Insights on the Role of Nitric Oxide in the Ovary: A Review of the Literature

2021 ◽  
Vol 18 (3) ◽  
pp. 980
Author(s):  
Maria Cristina Budani ◽  
Gian Mario Tiboni
Keyword(s):  
Nitric Oxide ◽  
In Vivo Studies ◽  
Published Data ◽  
Vitro Fertilization ◽  
Peripheral Neurons ◽  
Relevant Role ◽  
Oocyte Meiotic Maturation

Nitric oxide (NO) is formed during the oxidation of L-arginine to L-citrulline by the action of multiple isoenzymes of NO synthase (NOS): neuronal NOS (nNOS), endotelial NOS (eNOS), and inducible NOS (iNOS). NO plays a relevant role in the vascular endothelium, in central and peripheral neurons, and in immunity and inflammatory systems. In addition, several authors showed a consistent contribution of NO to different aspects of the reproductive physiology. The aim of the present review is to analyse the published data on the role of NO within the ovary. It has been demonstrated that the multiple isoenzymes of NOS are expressed and localized in the ovary of different species. More to the point, a consistent role was ascribed to NO in the processes of steroidogenesis, folliculogenesis, and oocyte meiotic maturation in in vitro and in vivo studies using animal models. Unfortunately, there are few nitric oxide data for humans; there are preliminary data on the implication of nitric oxide for oocyte/embryo quality and in-vitro fertilization/embryo transfer (IVF/ET) parameters. NO plays a remarkable role in the ovary, but more investigation is needed, in particular in the context of human ovarian physiology.

Sign in / Sign up

Export Citation Format

Share Document