scholarly journals A 75% Occurrence Rate of Debris Discs around F stars in the β Pic Moving Group

2021 ◽  
Author(s):  
Nicole Pawellek ◽  
Mark Wyatt ◽  
Luca Matrá ◽  
Grant Kennedy ◽  
Ben Yelverton
Keyword(s):  
Incidence Rate ◽  
Parameter Space ◽  
Occurrence Rate ◽  
Old Field ◽  
Radius Parameter ◽  
Young Clusters ◽  
Moving Groups ◽  
F Stars ◽  
Rule Out ◽  
Collisional Evolution

Abstract Only 20% of old field stars have detectable debris discs, leaving open the question of what disc, if any, is present around the remaining 80%. Young moving groups allow to probe this population, since discs are expected to have been brighter early on. This paper considers the population of F stars in the 23 Myr-old BPMG where we find that 9/12 targets possess discs. We also analyse archival ALMA data to derive radii for 4 of the discs, presenting the first image of the 63au radius disc of HD 164249. Comparing the BPMG results to disc samples from ∼45 Myr and ∼150 Myr-old moving groups, and to discs found around field stars, we find the disc incidence rate in young moving groups is comparable to that of the BPMG and significantly higher than that of field stars. The BPMG discs tend to be smaller than those around field stars. However, this difference is not statistically significant due to the small number of targets. Yet, by analysing the fractional luminosity vs disc radius parameter space we find that the fractional luminosities in the populations considered drop by two orders of magnitude within the first 100 Myr. This is much faster than expected by collisional evolution, implying a decay equivalent to 1/age2. We attribute this depletion to embedded planets which would be around 170 Mearth to cause a depletion on the appropriate timescale. However, we cannot rule out that different birth environments of nearby young clusters result in brighter debris discs than the progenitors of field stars which likely formed in a more dense environment.

scholarly journals The impact of structural error on parameter constraint in a climate model

2016 ◽  
Vol 7 (4) ◽  
pp. 917-935 ◽  
Author(s):  
Doug McNeall ◽  
Jonny Williams ◽  
Ben Booth ◽  
Richard Betts ◽  
Peter Challenor ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Parameter Space ◽  
Land Surface ◽  
History Matching ◽  
Climate Model ◽  
The Other ◽  
Future Climate Change ◽  
Amazon Forest ◽  
Structural Error ◽  
Rule Out

Abstract. Uncertainty in the simulation of the carbon cycle contributes significantly to uncertainty in the projections of future climate change. We use observations of forest fraction to constrain carbon cycle and land surface input parameters of the global climate model FAMOUS, in the presence of an uncertain structural error. Using an ensemble of climate model runs to build a computationally cheap statistical proxy (emulator) of the climate model, we use history matching to rule out input parameter settings where the corresponding climate model output is judged sufficiently different from observations, even allowing for uncertainty. Regions of parameter space where FAMOUS best simulates the Amazon forest fraction are incompatible with the regions where FAMOUS best simulates other forests, indicating a structural error in the model. We use the emulator to simulate the forest fraction at the best set of parameters implied by matching the model to the Amazon, Central African, South East Asian, and North American forests in turn. We can find parameters that lead to a realistic forest fraction in the Amazon, but that using the Amazon alone to tune the simulator would result in a significant overestimate of forest fraction in the other forests. Conversely, using the other forests to tune the simulator leads to a larger underestimate of the Amazon forest fraction. We use sensitivity analysis to find the parameters which have the most impact on simulator output and perform a history-matching exercise using credible estimates for simulator discrepancy and observational uncertainty terms. We are unable to constrain the parameters individually, but we rule out just under half of joint parameter space as being incompatible with forest observations. We discuss the possible sources of the discrepancy in the simulated Amazon, including missing processes in the land surface component and a bias in the climatology of the Amazon.

scholarly journals A Radial velocity survey of spatially resolved young, low-mass binaries

2018 ◽  
Vol 618 ◽  
pp. A5 ◽  
Author(s):  
Stephen Durkan ◽  
Markus Janson ◽  
Simona Ciceri ◽  
Wolfgang Brandner ◽  
Joshua Schlieder ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Solar Neighborhood ◽  
Activity Level ◽  
Activity Levels ◽  
Old Field ◽  
Triple Systems ◽  
Chromospheric Activity ◽  
Low Mass ◽  
Orbital Periods ◽  
Moving Groups

The identification and characterisation of low-mass binaries is of importance for a range of astrophysical investigations. Low-mass binaries in young (∼10–100 Myr) moving groups (YMGs) in the solar neighborhood are of particular significance as they provide unique opportunities to calibrate stellar models and evaluate the ages and coevality of the groups themselves. Low-mass M-dwarfs have pre-main sequence life times on the order of ∼100 Myr and therefore are continually evolving along a mass-luminosity track throughout the YMG phase, providing ideal laboratories for precise isochronal dating, if a model-independent dynamical mass can be measured. AstraLux lucky imaging multiplicity surveys have recently identified hundreds of new YMG low-mass binaries, where a subsample of M-dwarf multiples have estimated orbital periods less than 50 yr. We have conducted a radial velocity survey of a sample of 29 such targets to complement the astrometric data. This will allow enhanced orbital determinations and precise dynamical masses to be derived in a shorter timeframe than possible with astrometric monitoring alone, and allow for a more reliable isochronal analysis. Here we present radial velocity measurements derived for our sample over several epochs. We report the detection of the three-component spectroscopic multiple 2MASS J05301858-5358483, for which the C component is a new discovery, and forms a tight pair with the B component. Originally identified as a YMG member, we find that this system is a likely old field interloper, whose high chromospheric activity level is caused by tidal spin-up of the tight BC pair. Two other triple systems with a tight pair exist in the sample, 2MASS J04244260-0647313 (previously known) and 2MASS J20163382-0711456, but for the rest of the targets we find that additional tidally synchronized companions are highly unlikely, providing further evidence that their high chromospheric activity levels are generally signatures of youth.

scholarly journals Aspirin Decreases Hepatocellular Carcinoma Risk in Hepatitis C Virus Carriers: A Nationwide Cohort Study

2019 ◽  
Author(s):  
Yen-Hsiang Liao ◽  
Wen-Lin Hsu ◽  
Tzu-Hwei Wang ◽  
Chen-Ta Wu ◽  
Sheng-Yao Huang ◽  
...  
Keyword(s):  
Hepatocellular Carcinoma ◽  
Cohort Study ◽  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Propensity Score ◽  
Propensity Score Matching ◽  
Incidence Rate ◽  
Occurrence Rate ◽  
Control Group ◽  
Cancer Occurrence

Abstract Background Aspirin lowered some cancer occurrence rate, through the inhibition of the cyclooxygenase enzyme. The association of aspirin-use and hepatocellular carcinoma (HCC) occurrence rate in hepatitis B virus (HBV) carriers is well known. However, the association in hepatitis C virus (HCV) carriers is not known. Our purpose is comparing the HCC occurrence rate in HCV carriers with or without Aspirin treatment. Methods In this retrospective cohort study, the participants were ones newly-diagnosed with HCV from 2000 to 2012 in Taiwan. These HCV carriers with aspirin treatment were defined as the control group, whereas those without aspirin were defined as a compared cohort. We used a 1:1 propensity score matching by age, sex, comorbidities, drugs, diagnosis year and index year with covariate assessment. Results Our study sample consisted of 2980 aspirin-treated HCV carriers and 7771 non-aspirin-treated HCV carriers. After propensity score matching, each cohort consisted of 1911 HCV carriers. The adjusted hazard ratio (aHR) of HCC incidence in aspirin users (aHR=0.56, 95% CI=0.43-0.72, p < 0.001 ) was significantly lower than that in non-aspirin users. The Kaplan-Meier curves show that among the HCV carriers, aspirin users had a lower cumulative incidence rate of HCC in the first 10-year aspirin treatment course ( p < 0.0001 ). Conclusions The HCC incidence rate was lower in the aspirin users than non- aspirin users among HCV carriers, supporting the aspirin effect may be acting through inhibition of the cyclooxygenase enzyme pathway. Moreover, the patients got HCC protection by aspirin within 1-year treatment course and had best HCC prevention during 1- to 2-year aspirin treatment course. We encourage aspirin treatment to prevent HCC in HCV carriers.

scholarly journals Impact of treatment with anti-parasitic (Ivermectin) during prepartum period on mastitis and postpartum reproductive efficiency measurements in Egyptian Baladi cows

2021 ◽  
Author(s):  
Ahmed Ismail Damarany
Keyword(s):  
Incidence Rate ◽  
Reproductive Performance ◽  
The Other ◽  
Occurrence Rate ◽  
Reproductive Efficiency ◽  
Control Group ◽  
Current Investigation ◽  
Live Body Weight ◽  
Effect Of Treatment ◽  
Incident Rate

Abstract The current investigation was designed to determine the effect of treatment with anti-parasites (Ivermectin) on mastitis and postpartum reproductive efficiency measurements in Egyptian Baladi cows. Twenty-four of the cows included in this study were split into two groups. The first group (n = 12 cows) was injected two months prepartum with two doses (15 days inter-treatment) of IVOMEC® Plus solution subcutaneously behind the shoulder, 1ml/50kg live body weight as prescribed by the manufacturer, whilst the other group (n = 12 cows) was used as a control group. The present results revealed that the incident rate of mastitis in treated cows’ group was significantly (P < 0.05) lower (16.7%) than control cows’ group (41.7%). The conception rate in treated cows’ group was significantly (P < 0.05) higher (66.7%) compared with (33.3%) in control group. The time from calving to conception in treated cows was significantly (P < 0.05) lower 86.5 ± 11.4 days compared to 123.3 ± 13.2 days in the control group. The occurrence rate of anestrous cases was significantly (P < 0.05) lower (8.3%) in treated cows than (control group) (25%). In conclusion, the current study indicates there is an association between treated cows with anti-parasites (Ivermectin) two months prepartum and incidence rate of mastitis addition an improvement in the reproductive performance in treated cows relative to untreated cows. Therefore, the current study recommends the herdsmen treats their cows with anti-parasites (Ivermectin) during the prepartum period for less mastitis incidence rate and better reproductive efficiency.

Observation of TGFs at Mid Latitude

2021 ◽  
Author(s):  
Carolina Maiorana ◽  
Martino Marisaldi ◽  
Martin Füllekrug ◽  
Serge Soula ◽  
Jeff Lapierre ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Gamma Ray ◽  
Total Duration ◽  
Occurrence Rate ◽  
Atmospheric Absorption ◽  
Flash Rate ◽  
Global Population ◽  
Rule Out

&lt;p&gt;We present a sample of Terrestrial Gamma-ray Flashes (TGFs) observed at mid latitudes by the Atmosphere Space Interaction Monitor (ASIM). The events were detected over the period June 2018 - August 2020 in the latitude bands between 35&amp;#176; and 51&amp;#176; and between -35&amp;#176; and -51&amp;#176;; the sample includes the first observations above &amp;#177;38&amp;#176;. The characteristics of these mid-latitude events are consistent with the global population concerning the number of counts, but durations are significantly shorter. We also analyze the meteorological context and the general evolution of the parent storms and we show that the storms are not extreme in terms of total duration and extension. Finally, we present an estimation of the TGF occurrence rate at mid latitudes, based on ASIM's exposure, the local flash rate and tropopause altitude, and we show that it is outside but very close to two standard deviation from the rate of production at tropical latitudes, corrected by the higher atmospheric absorption of higher latitudes. This means that atmospheric absorption plays a major role in the detection of TGFs at mid latitudes, but we cannot rule out other factors.&lt;/p&gt;

Partitioning the Parameter Space According to Different Behaviors During Three-Dimensional Impacts

1995 ◽  
Vol 62 (3) ◽  
pp. 740-746 ◽  
Author(s):  
V. Bhatt ◽  
J. Koechling
Keyword(s):  
Parameter Space ◽  
Initial Conditions ◽  
Equations Of Motion ◽  
Three Dimensional ◽  
Flow Patterns ◽  
The Body ◽  
Qualitative Behavior ◽  
Sliding Velocity ◽  
Physical Behavior ◽  
Rule Out

The equations of motion that define three-dimensional rigid-body impact with finite friction and restitution cannot be solved in a closed form. Previous work has shown that for general shapes and initial conditions, the direction of sliding velocity keeps changing continuously throughout the duration of impact. The flow patterns defined by the trace of the sliding velocity can be classified into a finite number of qualitatively distinct physical behavior. We identify three dimensionless parameters that completely specify the sliding behavior, and determine regions in this parameter space that correspond to each of the different flow patterns. The qualitative behavior during impact can now be determined based on the region which contains the parameters for a given impact configuration. The analysis is also used to study the sensitivity of the sliding behavior to changes in shape or configuration of the body and to rule out the occurrence of certain ambiguities in the post-sticking behavior during impact.

scholarly journals Nearby Young Moving Groups: Statistical Methods and Challenges for Assigning Membership

2015 ◽  
Vol 10 (S314) ◽  
pp. 27-32
Author(s):  
L. Malo ◽  
J. Gagne ◽  
R. Doyon ◽  
D. Lafreniere ◽  
E. Artigau ◽  
...  
Keyword(s):  
Solar Neighborhood ◽  
Age Dating ◽  
Membership Probability ◽  
The Core ◽  
Global Properties ◽  
Chi Squared ◽  
Indicator Measurement ◽  
Moving Groups ◽  
Rule Out

AbstractYoung associations, being sparsely populated and relatively close to the Sun, their members are found all over the sky. In the Solar Neighborhood, young moving groups are found within 100 pc with ages ranging from 5 to 120 Myr. While known members of these groups were identified mostly through the Hipparcos data, only the most massive members have been fully characterized so far, and defined the core members. In the last decades, several new candidate members have been identified, using different approaches. Based on the global properties of the core members (kinematics and over luminosity), those methods used several criteria to establish the membership, from qualitative manner to quantitive methods using reduced chi-squared or membership probability. A full confirmation of the membership for those numerous candidates requires radial velocity and parallax measurements to confirm their kinematics, age-dating indicator measurement to assess their youth and multiplicity follow-up to rule out binary objects. In this proceeding, we summarize a general recipe to assign membership, describe the numerous challenges for assigning membership, and end with a discussion on the appropriateness and reliability of the BANYAN I and II tools to assess membership.

scholarly journals The bright end of the exo-Zodi luminosity function: Disk evolution and implications for exo-Earth detectability

2013 ◽  
Vol 8 (S299) ◽  
pp. 194-198
Author(s):  
G. M. Kennedy ◽  
M. C. Wyatt
Keyword(s):  
Luminosity Function ◽  
Main Sequence ◽  
Terrestrial Planet ◽  
Occurrence Rate ◽  
Main Sequence Stars ◽  
Planetary Dynamics ◽  
Disk Evolution ◽  
Cometary Origin ◽  
Rule Out

AbstractThis contribution summarises the first characterisation of the 12 μm warm dust (“exo-Zodi”) luminosity function around Sun-like stars, focussing on the dustiest systems that can be identified by the WISE mission (Kennedy & Wyatt 2013). We use the sample of main-sequence stars observed by Hipparcos within 150pc as an unbiased sample, and report the detection of six new warm dust candidates. The ages of five of these new sources are unknown, meaning that they may be sites of terrestrial planet formation or rare analogues of other old warm dust systems. We show that the dustiest old (> Gyr) systems such as BD+20 307 are 1 in 10,000 occurrences. Bright warm dust is much more common around young (<120 Myr) systems, with a ~1% occurrence rate. We show that a two component in situ model where all stars have initially massive warm disks and in which warm debris is also generated at some random time along the stars' main-sequence lifetime, perhaps due to a collision, can explain the observations. However, if all stars only have initially massive warm disks these would not be visible at Gyr ages, and random collisions on the main-sequence are too infrequent to explain the high disk occurrence rate for young stars. That is, neither component can explain the observations on their own. Despite these conclusions, we cannot rule out an alternative dynamical model in which comets are scattered in from outer regions because the distribution of systems with the appropriate dynamics is unknown. Our in situ model predicts that the fraction of stars with exo-Zodi bright enough to cause problems for future exo-Earth imaging attempts is at least roughly 10%, and is higher for populations of stars younger than a few Gyr. This prediction of roughly 10% also applies to old stars because bright systems like BD+20 307 imply a population of fainter systems that were once bright, but are now decaying through fainter levels. Our prediction should be strongly tested by the Large Binocular Telescope Interferometer, which will provide valuable constraints and input for more detailed evolution models. A detection fraction lower than our prediction could indicate that the hot dust in systems like BD+20 307 has a cometary origin due to the quirks of the planetary dynamics. Population models of comet delivery need to be developed to help distinguish between different possible origins of warm dust.

VARIATIONS IN THE INTRINSIC STRENGTH OF THE 1956 QUADRANTID METEOR SHOWER

1957 ◽  
Vol 35 (6) ◽  
pp. 703-711 ◽  
Author(s):  
C. O. Hines ◽  
E. L. Vogan
Keyword(s):  
Incidence Rate ◽  
Detection Rate ◽  
Meteor Shower ◽  
New Technique ◽  
Occurrence Rate ◽  
Meteor Stream ◽  
Forward Scatter ◽  
Scatter Theory ◽  
Intrinsic Strength

The occurrence rate of meteoric signals, detected on a V.H.F. forward-scatter path, is analyzed for the time of the 1956 Quadrantid shower. The detection rate of the shower meteors is converted to an incidence rate, by use of the appropriate forward-scatter theory. The variation in the intrinsic strength of the shower is thereby determined, on an hour-to-hour basis, and it is compared with variations which have been obtained in other years by other methods. The comparison reveals a distinct secular shifting of the orbit of the Quadrantid meteor stream. It also illustrates the marked advantage of the new technique in assessing variations in the strengths of short-lived showers.

scholarly journals Constraints on Cold HI in the Halo of NGC 3079 from Absorption Measurements of Q0957+561

1999 ◽  
Vol 16 (1) ◽  
pp. 89-94 ◽  
Author(s):  
Judith A. Irwin ◽  
Lawrence M. Widrow ◽  
Jayanne English
Keyword(s):  
Dark Matter ◽  
Fractal Dimension ◽  
Parameter Space ◽  
Upper Limit ◽  
Observational Test ◽  
No Absorption ◽  
Absorption Measurements ◽  
Rule Out

AbstractWe perform the first observational test of dark matter in the form of cold (3 K) fractal clouds, as described by Pfenniger et al. (1994) and Pfenniger & Combes (1994). This is accomplished by probing for HI absorption in the halo of NGC 3079 against the background quasar, Q 0957+561, which is separated from the centre of NGC 3079 by 64 kpc, in projection. No absorption is detected to a limit of 3ΔTb/(–Tc) = 0·01. We have considered models for HI + H2 clouds characterised by the cloud radius and fractal dimension. Using the upper limit on absorption, we have ruled out a limited but interesting region of this parameter space. The observations do not rule out the possibility that all the dark matter could be hidden in the form of cold fractal clouds. By contrast, if the gas is diffuse with unity filling factors, then HI cannot constitute more than ∼ 10−5, by mass, of the galaxy's dark matter.

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