scholarly journals KMOS study of the mass accretion rate from Class I to Class II in NGC 1333

2021 ◽  
Author(s):  
E. Fiorellino ◽  
C.F. Manara ◽  
B. Nisini ◽  
S. Ramsay ◽  
Keyword(s):  
Accretion Rate ◽  
Class Ii ◽  
Class I ◽  
Mass Accretion Rate

scholarly journals Physical and chemical fingerprint of protostellar disc formation

2019 ◽  
Vol 626 ◽  
pp. A71 ◽  
Author(s):  
E. Artur de la Villarmois ◽  
J. K. Jørgensen ◽  
L. E. Kristensen ◽  
E. A. Bergin ◽  
D. Harsono ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Accretion Rate ◽  
Stellar Mass ◽  
Class I ◽  
High Angular Resolution ◽  
Mass Accretion Rate ◽  
Bolometric Luminosity ◽  
Stellar Masses ◽  
Physical And Chemical ◽  
The Continuum

Context. The structure and composition of emerging planetary systems are likely strongly influenced by their natal environment within the protoplanetary disc at the time when the star is still gaining mass. It is therefore essential to identify and study the physical processes at play in the gas and dust close to young protostars and investigate the chemical composition of the material that is inherited from the parental cloud. Aims. The purpose of this paper is to explore and compare the physical and chemical structure of Class I low-mass protostellar sources on protoplanetary disc scales. Methods. We present a study of the dust and gas emission towards a representative sample of 12 Class I protostars from the Ophiuchus molecular cloud with the Atacama Large Millimeter/submillimeter Array (ALMA). The continuum at 0.87 mm and molecular transitions from C17O, C34S, H13CO+, CH3OH, SO2, and C2H were observed at high angular resolution (0.′′4, ~60 au diameter) towards each source. The spectrally and spatially resolved maps reveal the kinematics and the spatial distribution of each species. Moreover, disc and stellar masses are estimated from the continuum flux and position-velocity diagrams, respectively. Results. Six of the sources show disc-like structures in C17O, C34S, or H13CO+ emission. Towards the more luminous sources, compact emission and large line widths are seen for transitions of SO2 that probe warm gas (Eu ~ 200 K). In contrast, C17O emission is detected towards the least evolved and less luminous systems. No emission of CH3OH is detected towards any of the continuum peaks, indicating an absence of warm CH3OH gas towards these sources. Conclusions. A trend of increasing stellar mass is observed as the envelope mass decreases. In addition, a power-law relation is seen between the stellar mass and the bolometric luminosity, corresponding to a mass accretion rate of (2.4 ± 0.6) × 10−7 M⊙ yr−1 for the Class I sources, with a minimum and maximum value of 7.5 × 10−8 and 7.6 × 10−7 M⊙ yr−1, respectively. This mass accretion rate is lower than the expected value if the accretion is constant in time and rather points to a scenario of accretion occurring in bursts. The differentiation between C17O and SO2 suggests that they trace different physical components: C17O traces the densest and colder regions of the disc-envelope system, while SO2 may be associated with regions of higher temperature, such as accretion shocks. The lack of warm CH3OH emission suggests that there is no hot-core-like region around any of the sources and that the CH3OH column density averaged over the disc is low. Finally, the combination of bolometric temperature and luminosity may indicate an evolutionarytrend of chemical composition during these early stages.

Electron microscopy analysis of degenerating pancreatic ß cells in transgenic mice expressing the MHC Class I antigen Dd

1990 ◽  
Vol 48 (3) ◽  
pp. 548-549
Author(s):  
T. A. Stewart ◽  
D. Liggitt ◽  
S. Pitts ◽  
L. Martin ◽  
M. Siegel ◽  
...  
Keyword(s):  
Type I Diabetes ◽  
Disease Process ◽  
Class Ii ◽  
Class I ◽  
Type I ◽  
Aberrant Expression ◽  
Mhc Molecules ◽  
Endogenous Insulin ◽  
Class Ii Mhc ◽  
Ifn Γ

Insulin-dependant (Type I) diabetes mellitus (IDDM) is a metabolic disorder resulting from the lack of endogenous insulin secretion. The disease is thought to result from the autoimmune mediated destruction of the insulin producing ß cells within the islets of Langerhans. The disease process is probably triggered by environmental agents, e.g. virus or chemical toxins on a background of genetic susceptibility associated with particular alleles within the major histocompatiblity complex (MHC). The relation between IDDM and the MHC locus has been reinforced by the demonstration of both class I and class II MHC proteins on the surface of ß cells from newly diagnosed patients as well as mounting evidence that IDDM has an autoimmune pathogenesis. In 1984, a series of observations were used to advance a hypothesis, in which it was suggested that aberrant expression of class II MHC molecules, perhaps induced by gamma-interferon (IFN γ) could present self antigens and initiate an autoimmune disease. We have tested some aspects of this model and demonstrated that expression of IFN γ by pancreatic ß cells can initiate an inflammatory destruction of both the islets and pancreas and does lead to IDDM.

Pictish Horse Carvings

1991 ◽  
Vol 17 (1) ◽  
pp. 53-62
Author(s):  
Irene Hughson
Keyword(s):  
Class Ii ◽  
Class I ◽  
Early Historic Period ◽  
High Quality ◽  
Historic Period ◽  
Agricultural Economy ◽  
Different Types ◽  
Early Historic

Summary This paper examines the horse carvings to be found on Class I and Class II Pictish sculptured stones and considers their reliability as evidence of the sort of horses and ponies that would have existed in the Early Historic Period. An attempt is made to show that the availability in Britain of good sized, high quality riding horses during that period is not inconsistent with what is known of the development and distribution of different types of horses in pre-hislory. The importance of horses and ponies in Early Historic societies is stressed and inferences drawn about the agricultural economy that could support horses and the skilled specialists required to look after them.

MHC Sınıf I ve MHC Sınıf II Gen Düzenlenmesi

2020 ◽  
Vol 8 (3) ◽  
pp. 144-156
Author(s):  
Şule KARATAŞ ◽  
Fatma SAVRAN OĞUZ
Keyword(s):  
Immune Response ◽  
T Cells ◽  
Gene Regulation ◽  
Mhc Class I ◽  
Mhc Class Ii ◽  
Class Ii ◽  
Class I ◽  
Mhc Molecules ◽  
Class Ii Mhc ◽  
Regulation Mechanisms

Introduction: Peptides obtained by processing intracellular and extracellular antigens are presented to T cells to stimulate the immune response. This presentation is made by peptide receptors called major histocompatibility complex (MHC) molecules. The regulation mechanisms of MHC molecules, which have similar roles in the immune response, especially at the gene level, have significant differences according to their class. Objective: Class I and class II MHC molecules encoded by MHC genes on the short arm of the sixth chromosome are peptide receptors that stimulate T cell response. These peptides, which will enable the recognition of the antigen from which they originate, are loaded into MHC molecules and presented to T cells. Although the principles of loading and delivering peptides are similar for both molecules, the peptide sources and peptide loading mechanisms are different. In addition, class I molecules are expressed in all nucleated cells while class II molecules are expressed only in Antigen Presentation Cells (APC). These differences; It shows that MHC class I is not expressed by exactly the same transcriptional mechanisms as MHC class II. In our article, we aimed to compare the gene expressions of both classes and reveal their similarities and differences. Discussion and Conclusion: A better understanding of the transcriptional mechanisms of MHC molecules will reveal the role of these molecules in diseases more clearly. In our review, we discussed MHC gene regulation mechanisms with presence of existing informations, which is specific to the MHC class, for contribute to future research. Keywords: MHC class I, MHC class II, MHC gene regulation, promoter, SXY module, transcription

Sign in / Sign up

Export Citation Format

Share Document