326 research outputs found
Physical Education 2
Exam paper for first semester 201
Hallmarks of cancer-the new testament.
Diagnosis and treatment of disease demand a sound understanding of the underlying mechanisms, determining any Achilles' heel that can be targeted in effective therapies. Throughout history, this endeavour to decipher the origin and mechanism of transformation of a normal cell into cancer has led to various theories-from cancer as a curse to an understanding at the level of single-cell heterogeneity, meaning even among a single sub-type of cancer there are myriad molecular challenges to overcome. With increasing insight into cancer genetics and biology, the disease has become ever more complex to understand. The complexity of cancer as a disease was distilled into key traits by Hanahan and Weinberg in their seminal 'Hallmarks of Cancer' reviews. This lucid conceptualization of complex cancer biology is widely accepted and has helped advance cancer therapeutics by targeting the various hallmarks but, with the advancement in technologies, there is greater granularity in how we view cancer as a disease, and the additional understanding over the past decade requires us to revisit the hallmarks of cancer. Based on extensive study of the cancer research literature, we propose four novel hallmarks of cancer, namely, the ability of cells to regress from a specific specialized functional state, epigenetic changes that can affect gene expression, the role of microorganisms and neuronal signalling, to be included in the hallmark conceptualization along with evidence of various means to exploit them therapeutically
The magnetic field and multiple planets of the young dwarf AU~Mic
In this paper we present an analysis of near-infrared spectropolarimetric and
velocimetric data of the young M dwarf AU Mic, collected with SPIRou at the
Canada-France-Hawaii telescope from 2019 to 2022, mostly within the SPIRou
Legacy Survey. With these data, we study the large- and small-scale magnetic
field of AU Mic, detected through the unpolarized and circularly-polarized
Zeeman signatures of spectral lines. We find that both are modulated with the
stellar rotation period (4.86 d), and evolve on a timescale of months under
differential rotation and intrinsic variability. The small-scale field,
estimated from the broadening of spectral lines, reaches kG. The
large-scale field, inferred with Zeeman-Doppler imaging from Least-Squares
Deconvolved profiles of circularly-polarized and unpolarized spectral lines, is
mostly poloidal and axisymmetric, with an average intensity of G. We
also find that surface differential rotation, as derived from the large-scale
field, is 30% weaker than that of the Sun. We detect the radial
velocity (RV) signatures of transiting planets b and c, although dwarfed by
activity, and put an upper limit on that of candidate planet d, putatively
causing the transit-timing variations of b and c. We also report the detection
of the RV signature of a new candidate planet (e) orbiting further out with a
period of d, i.e., near the 4:1 resonance with b. The RV
signature of e is detected at 6.5 while those of b and c show up at
4, yielding masses of and
Earth masses for b and c, and a minimum mass of
Earth masses for e.Comment: MNRAS, in press (20 pages and 12 figures + 9 pages of supplementary
material
: a data-driven approach to correct for systematics in RV data -- Application to SPIRou data of the planet-hosting M dwarf GJ 251
Context: Recent advances in the development of precise radial velocity (RV)
instruments in the near-infrared (nIR) domain, such as SPIRou, have facilitated
the study of M-type stars to more effectively characterize planetary systems.
However, the nIR presents unique challenges in exoplanet detection due to
various sources of planet-independent signals which can result in systematic
errors in the RV data.
Aims: In order to address the challenges posed by the detection of
exoplanetary systems around M-type stars using nIR observations, we introduce a
new data-driven approach for correcting systematic errors in RV data. The
effectiveness of this method is demonstrated through its application to the
star GJ 251.
Methods: Our proposed method, referred to as (Weighted
principAl comPonent analysIs reconsTructIon), uses a dataset of per-line RV
time-series generated by the line-by-line (LBL) algorithm and employs a
weighted principal component analysis (wPCA) to reconstruct the original RV
time-series. A multi-step process is employed to determine the appropriate
number of components, with the ultimate goal of subtracting the wPCA
reconstruction of the per-line RV time-series from the original data in order
to correct systematic errors.
Results: The application of to GJ 251 successfully
eliminates spurious signals from the RV time-series and enables the first
detection in the nIR of GJ 251b, a known temperate super-Earth with an orbital
period of 14.2 days. This demonstrates that, even when systematics in SPIRou
data are unidentified, it is still possible to effectively address them and
fully realize the instrument's capability for exoplanet detection.
Additionally, in contrast to the use of optical RVs, this detection did not
require to filter out stellar activity, highlighting a key advantage of nIR RV
measurements.Comment: Submitted to A&A. For the publicly available Wapiti code, see
https://github.com/HkmMerwan/wapit
Monitoring the large-scale magnetic field of AD~Leo with SPIRou, ESPaDOnS and Narval. Toward a magnetic polarity reversal?
One manifestation of dynamo action on the Sun is the 22-yr magnetic cycle,
exhibiting a polarity reversal and a periodic conversion between poloidal and
toroidal fields. For M dwarfs, several authors claim evidence of activity
cycles from photometry and analyses of spectroscopic indices, but no clear
polarity reversal has been identified from spectropolarimetric observations.
Our aim is to monitor the evolution of the large-scale field of AD Leo, which
has shown hints of a secular evolution from past dedicated spectropolarimetric
campaigns. We analysed near-infrared spectropolarimetric observations of the
active M dwarf AD Leo taken with SPIRou between 2019 and 2020 and archival
optical data collected with ESPaDOnS and Narval between 2006 and 2019. We
searched for long-term variability in the longitudinal field, the width of
unpolarised Stokes profiles, the unsigned magnetic flux derived from Zeeman
broadening, and the geometry of the large-scale magnetic field using both
Zeeman-Doppler Imaging and Principal Component Analysis. We found evidence of a
long-term evolution of the magnetic field, featuring a decrease in axisymmetry
(from 99% to 60%). This is accompanied by a weakening of the longitudinal field
(-300 to -50 G) and a correlated increase in the unsigned magnetic flux (2.8 to
3.6 kG). Likewise, the width of the mean profile computed with selected
near-infrared lines manifests a long-term evolution corresponding to field
strength changes over the full time series, but does not exhibit modulation
with the stellar rotation of AD Leo in individual epochs. The large-scale
magnetic field of AD Leo manifested first hints of a polarity reversal in late
2020 in the form of a substantially increased dipole obliquity, while the
topology remained predominantly poloidal and dipolar. This suggests that
low-mass M dwarfs with a dipole-dominated magnetic field can undergo magnetic
cycles.Comment: 26 pages, 18 figures, 8 table
CO or no CO? Narrowing the CO abundance constraint and recovering the H2O detection in the atmosphere of WASP-127 b using SPIRou
Precise measurements of chemical abundances in planetary atmospheres are
necessary to constrain the formation histories of exoplanets. A recent study of
WASP-127b, a close-in puffy sub-Saturn orbiting its solar-type host star in 4.2
d, using HST and Spitzer revealed a feature-rich transmission spectrum with
strong excess absorption at 4.5 um. However, the limited spectral resolution
and coverage of these instruments could not distinguish between CO and/or CO2
absorption causing this signal, with both low and high C/O ratio scenarios
being possible. Here we present near-infrared (0.9--2.5 um) transit
observations of WASP-127 b using the high-resolution SPIRou spectrograph, with
the goal to disentangle CO from CO2 through the 2.3 um CO band. With SPIRou, we
detect H2O at a t-test significance of 5.3 sigma and observe a tentative (3
sigma) signal consistent with OH absorption. From a joint SPIRou + HST +
Spitzer retrieval analysis, we rule out a CO-rich scenario by placing an upper
limit on the CO abundance of log10[CO]<-4.0, and estimate a log10[CO2] of
-3.7^(+0.8)_(-0.6), which is the level needed to match the excess absorption
seen at 4.5um. We also set abundance constraints on other major C-, O-, and
N-bearing molecules, with our results favoring low C/O (0.10^(+0.10)_(-0.06)),
disequilibrium chemistry scenarios. We further discuss the implications of our
results in the context of planet formation. Additional observations at high and
low-resolution will be needed to confirm these results and better our
understanding of this unusual world.Comment: 23 pages, 13 figures, Submitted for publication in the Monthly Notice
of the Royal Astronomical Societ
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