195 research outputs found
Aggregates relaxation in a jamming colloidal suspension after shear cessation
The reversible aggregates formation in a shear thickening, concentrated
colloidal suspension is investigated through speckle visibility spectroscopy, a
dynamic light scattering technique recently introduced [P.K. Dixon and D.J.
Durian, Phys. Rev. Lett. 90, 184302 (2003)]. Formation of particles aggregates
is observed in the jamming regime, and their relaxation after shear cessation
is monitored as a function of the applied shear stress. The aggregates
relaxation time increases when a larger stress is applied. Several phenomena
have been proposed to interpret this behavior: an increase of the aggregates
size and volume fraction, or a closer packing of the particles in the
aggregates.Comment: 7 pages, 7 figures; added figures included in the pdf versio
Spontaneous electric fields in solid carbon monoxide
Reflection–absorption infrared spectroscopy (RAIRS) is shown to provide a means of observing the spontelectric phase of matter, the defining characteristic of which is the occurrence of a spontaneous and powerful static electric field within a film of material.</p
Genetic compatibility exceeds possible ‘good genes’ effects of sexual selection in lake char
Mating is rarely random in nature, but the effects of mate choice on offspring performance are still poorly understood. We sampled in total 47 wild lake char (Salvelinus umbla) during two breeding seasons and used their gametes to investigate the genetic consequences of different mating scenarios. In a first study, 1,464 embryos that resulted from sperm competition trials were raised singly in either a stress- or non-stress environment. Offspring growth turned out to be strongly reduced with increased genetic relatedness between the parents while male coloration (that reveal aspects of male health) was no significant predictor of offspring performance. In a second experiment one year later, block-wise full-factorial in vitro breeding was used to produce 3,094 embryos that were raised singly after sublethal exposures to a pathogen or water only. Offspring growth was again strongly reduced with increased genetic relatedness between the parents while male coloration was no significant predictor of offspring performance. We conclude that the genetic benefits of mate choice would be strongest if females avoided genetic similarity, while male breeding colors seem more relevant in intra-sexual selection
Photothermal Heterodyne Imaging of Individual Metallic Nanoparticles: Theory versus Experiments
We present the theoretical and detailed experimental characterizations of
Photothermal Heterodyne Imaging. An analytical expression of the photothermal
heterodyne signal is derived using the theory of light scattering from a
fluctuating medium. The amplitudes of the signals detected in the backward and
forward configurations are compared and their frequency dependences are
studied. The application of the Photothermal Heterodyne detection technique to
the absorption spectroscopy of individual gold nanoparticles is discussed and
the detection of small individual silver nanoparticles is demonstrated
Single NanoParticle Photothermal Tracking (SNaPT) of 5 nm gold beads in live cells
Tracking individual nano-objets in live cells during arbitrary long times is
an ubiquitous need in modern biology. We present here a method for tracking
individual 5 nm gold nanoparticles on live cells. It relies on the photothermal
effect and the detection of the Laser Induced Scattering around a NanoAbsorber
(LISNA). The key point for recording trajectories at video rate is the use of a
triangulation procedure. The effectiveness of the method is tested against
Single fluorescent Molecule Tracking in live COS7 cells on subsecond time
scales. We further demonstrate recordings for several minutes of AMPA receptors
trajectories on the plasma membrane of live neurons. SNaPT has the unique
potential to record arbitrary long trajectory of membrane proteins using
non-fluorescent nanometer sized labels
Gaia Data Release 3: G_RVS photometry from the RVS spectra
Gaia Data Release 3 (DR3) contains the first release of magnitudes estimated
from the integration of Radial Velocity Spectrometer (RVS) spectra for a sample
of about 32.2 million stars brighter than G_RVS~14 mag (or G~15 mag). In this
paper, we describe the data used and the approach adopted to derive and
validate the G_RVS magnitudes published in DR3. We also provide estimates of
the G_RVS passband and associated G_RVS zero-point. We derived G_RVS photometry
from the integration of RVS spectra over the wavelength range from 846 to 870
nm. We processed these spectra following a procedure similar to that used for
DR2, but incorporating several improvements that allow a better estimation of
G_RVS. These improvements pertain to the stray-light background estimation, the
line spread function calibration, and the detection of spectra contaminated by
nearby relatively bright sources. We calibrated the G_RVS zero-point every 30
hours based on the reference magnitudes of constant stars from the Hipparcos
catalogue, and used them to transform the integrated flux of the cleaned and
calibrated spectra into epoch magnitudes. The G_RVS magnitude of a star
published in DR3 is the median of the epoch magnitudes for that star. We
estimated the G_RVS passband by comparing the RVS spectra of 108 bright stars
with their flux-calibrated spectra from external spectrophotometric libraries.
The G_RVS magnitude provides information that is complementary to that obtained
from the G, G_BP, and G_RP magnitudes, which is useful for constraining stellar
metallicity and interstellar extinction. The median precision of G_RVS
measurements ranges from about 0.006 mag for the brighter stars (i.e. with 3.5
< G_RVS < 6.5 mag) to 0.125 mag at the faint end. The derived G_RVS passband
shows that the effective transmittance of the RVS is approximately 1.23 times
better than the pre-launch estimate.Comment: 16 pages, 18 figures. Accepted for publication in A&
Gaia Data Release 3
CONTEXT:
Gaia Data Release 3 (Gaia DR3) contains the second release of the combined radial velocities. It is based on the spectra collected during the first 34 months of the nominal mission. The longer time baseline and the improvements of the pipeline made it possible to push the processing limit from GRVS = 12 in Gaia DR2 to GRVS = 14 mag.
AIMS:
We describe the new functionalities implemented for Gaia DR3, the quality filters applied during processing and post-processing, and the properties and performance of the published velocities.
METHODS:
For Gaia DR3, several functionalities were upgraded or added to the spectroscopic pipeline. The calibrations were improved in order to better model the temporal evolution of the straylight and of the instrumental point spread function (PSF). The overlapped spectra, which were mostly discarded in Gaia DR2, are now handled by a dedicated module. The hot star template mismatch, which prevented publication of hot stars in Gaia DR2, is largely mitigated now, down to GRVS = 12 mag. The combined radial velocity of stars brighter than or equal to GRVS = 12 mag is calculated in the same way as in Gaia DR2, that is, as the median of the epoch radial velocity time series. The combined radial velocity of the fainter stars is measured from the average of the cross-correlation functions.
RESULTS:
Gaia DR3 contains the combined radial velocities of 33 812 183 stars. With respect to Gaia DR2, the temperature interval has been expanded from Teff ∈ [3600, 6750] K to Teff ∈ [3100, 14 500] K for the bright stars (GRVS ≤ 12 mag) and [3100, 6750] K for the fainter stars. The radial velocities sample a significant part of the Milky Way: they reach a few kiloparsecs beyond the Galactic centre in the disc and up to about 10−15 kpc vertically into the inner halo. The median formal precision of the velocities is 1.3 km s−1 at GRVS = 12 and 6.4 km s−1 at GRVS = 14 mag. The velocity zeropoint exhibits a small systematic trend with magnitude that starts around GRVS = 11 mag and reaches about 400 m s−1 at GRVS = 14 mag. A correction formula is provided that can be applied to the published data. The Gaia DR3 velocity scale agrees satisfactorily with APOGEE, GALAH, GES, and RAVE; the systematic differences mostly remain below a few hundred m s−1. The properties of the radial velocities are also illustrated with specific objects: open clusters, globular clusters, and the Large Magellanic Cloud. For example, the precision of the data allows mapping the line-of-sight rotational velocities of the globular cluster 47 Tuc and of the Large Magellanic Cloud
Gaia Early Data Release 3: Summary of the contents and survey properties
ABSTRACT: Context. We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2.
Aims. A summary of the contents of Gaia EDR3 is presented, accompanied by a discussion on the differences with respect to Gaia DR2 and an overview of the main limitations which are present in the survey. Recommendations are made on the responsible use of Gaia EDR3 results.
Methods. The raw data collected with the Gaia instruments during the first 34 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium and turned into this early third data release, which represents a major advance with respect to Gaia DR2 in terms of astrometric and photometric precision, accuracy, and homogeneity.
Results. Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the (GBP ? GRP) colour are also available. The passbands for G, GBP, and GRP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia-CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3. Conclusions. Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 per cent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30-40% for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G, GBP, and GRP is valid over the entire magnitude and colour range, with no systematics above the 1% levelThe Gaia mission and data processing have financially been supported by ; the Spanish Ministry of Economy (MINECO/FEDER, UE) through grants ESP2016-80079-C2-1-R, ESP2016-80079-C2-2-R, RTI2018-095076-B-C21, RTI2018-095076-B-C22, BES-2016-078499, and BES-2017-083126 and the Juan de la Cierva formación 2015 grant FJCI-2015-2671, the Spanish Ministry of Education, Culture, and Sports through grant FPU16/03827, the Spanish Ministry of Science and Innovation (MICINN) through grant
AYA2017-89841P for project “Estudio de las propiedades de los fósiles estelares en el entorno del Grupo Local” and through grant TIN2015-65316-P for project
“Computación de Altas Prestaciones VII
Gaia Early Data Release 3 Acceleration of the Solar System from Gaia astrometry
Context. Gaia Early Data Release 3 (Gaia EDR3) provides accurate astrometry for about 1.6 million compact (QSO-like) extragalactic sources, 1.2 million of which have the best-quality five-parameter astrometric solutions. Aims. The proper motions of QSO-like sources are used to reveal a systematic pattern due to the acceleration of the solar systembarycentre with respect to the rest frame of the Universe. Apart from being an important scientific result by itself, the acceleration measured in this way is a good quality indicator of the Gaia astrometric solution. Methods. Theeffect of the acceleration was obtained as a part of the general expansion of the vector field of proper motions in vector spherical harmonics (VSH). Various versions of the VSH fit and various subsets of the sources were tried and compared to get the most consistent result and a realistic estimate of its uncertainty. Additional tests with the Gaia astrometric solution were used to get a better idea of the possible systematic errors in the estimate. Results. Our best estimate of the acceleration based on Gaia EDR3 is (2.32 +/- 0.16) x 10(-10) m s(-2) (or 7.33 +/- 0.51 km s(-1) Myr-1) towards alpha = 269.1 degrees +/- 5.4 degrees, delta = -31.6 degrees +/- 4.1 degrees, corresponding to a proper motion amplitude of 5.05 +/- 0.35 mu as yr(-1). This is in good agreement with the acceleration expected from current models of the Galactic gravitational potential. We expect that future Gaia data releases will provide estimates of the acceleration with uncertainties substantially below 0.1 mu as yr(-1).Peer reviewe
Gaia Data Release 3: Mapping the asymmetric disc of the Milky Way
With the most recent Gaia data release the number of sources with complete 6D
phase space information (position and velocity) has increased to well over 33
million stars, while stellar astrophysical parameters are provided for more
than 470 million sources, in addition to the identification of over 11 million
variable stars. Using the astrophysical parameters and variability
classifications provided in Gaia DR3, we select various stellar populations to
explore and identify non-axisymmetric features in the disc of the Milky Way in
both configuration and velocity space. Using more about 580 thousand sources
identified as hot OB stars, together with 988 known open clusters younger than
100 million years, we map the spiral structure associated with star formation
4-5 kpc from the Sun. We select over 2800 Classical Cepheids younger than 200
million years, which show spiral features extending as far as 10 kpc from the
Sun in the outer disc. We also identify more than 8.7 million sources on the
red giant branch (RGB), of which 5.7 million have line-of-sight velocities,
allowing the velocity field of the Milky Way to be mapped as far as 8 kpc from
the Sun, including the inner disc. The spiral structure revealed by the young
populations is consistent with recent results using Gaia EDR3 astrometry and
source lists based on near infrared photometry, showing the Local (Orion) arm
to be at least 8 kpc long, and an outer arm consistent with what is seen in HI
surveys, which seems to be a continuation of the Perseus arm into the third
quadrant. Meanwhile, the subset of RGB stars with velocities clearly reveals
the large scale kinematic signature of the bar in the inner disc, as well as
evidence of streaming motions in the outer disc that might be associated with
spiral arms or bar resonances. (abridged
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