1,025 research outputs found
Exploring sources of variation in thermoluminescence emissions and anomalous fading in alkali feldspars
Alkali feldspar is routinely used in retrospective dosimetry using luminescence methods. However there is a signal loss over time, termed âanomalous fadingâ, which results in age underestimation if uncorrected. Although significant improvements have been made in recent years, luminescence dating of feldspars remains challenging. This paper investigates the relationships between chemistry, structural state and the scale of exsolution with thermoluminescence (TL) emission spectra and infrared stimulated luminescence (IRSL) fading rates.
We measure TL emission spectra, where possible linking the recombination site to physical features of the feldspar crystals. We show that fading rates are lowest in ordered end-member Na- and K-feldspars but significantly greater in disordered end-members, showing that AlâSi order influences fading. As well as having very low fading rates, ordered end-member samples have distinctive TL emission spectra, with the yellow-green emission dominant, while all other samples have a dominant blue emission. Perthite, i.e. exsolved members of the (Na,K)-feldspar solid solution, show greater fading than disordered end-members and fading is greatest in semi-coherent macroperthite. We propose that the state of AlâSi-order, and the occurrence of defects and dislocations at the perthite lamellar interfaces influence anomalous fading rates in feldspar
Combined ion and atom trap for low temperature ion-atom physics
We report an experimental apparatus and technique which simultaneously traps
ions and cold atoms with spatial overlap. Such an apparatus is motivated by the
study of ion-atom processes at temperatures ranging from hot to ultra-cold.
This area is a largely unexplored domain of physics with cold trapped atoms. In
this article we discuss the general design considerations for combining these
two traps and present our experimental setup. The ion trap and atom traps are
characterized independently of each other. The simultaneous operation of both
is then described and experimental signatures of the effect of the ions and
cold-atoms on each other are presented. In conclusion the use of such an
instrument for several problems in physics and chemistry is briefly discussed.Comment: 24 pages, 13 figures. Figures Fixe
The Mars Science Laboratory record of optical depth measurements via solar imaging
Acknowledgments We are grateful to the teams that developed, landed, and operated Curiosity on Mars, allowing for the present study. The research was conducted partly at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). MTL was supported via sub-contract 18-1187 from Malin Space Science Systems, Inc. SDG was supported by the MSL Participating Scientist program. JMB was supported by MSL Participating Scientist Grant 80NSSC22K0657. AV-R was supported by the Comunidad de Madrid Project S2018/NMT-4291 (TEC2SPACE-CM). M-PZ was supported by grant PID2019-104205GB-C21 funded by MCIN/AEI/10.13039/501100011033. JM-T was supported by UK Space Agency projects ST/W00190X/1 and ST/V00610X/1.Peer reviewedPostprin
k=0Magnetic Structure and Absence of Ferroelectricity in SmFeO3
SmFeO3 has attracted considerable attention very recently due to the reported
multiferroic properties above room-temperature. We have performed powder and
single crystal neutron diffraction as well as complementary polarization
dependent soft X-ray absorption spectroscopy measurements on floating-zone
grown SmFeO3 single crystals in order to determine its magnetic structure. We
found a k=0 G-type collinear antiferromagnetic structure that is not compatible
with inverse Dzyaloshinskii-Moriya interaction driven ferroelectricity. While
the structural data reveals a clear sign for magneto-elastic coupling at the
N\'eel-temperature of ~675 K, the dielectric measurements remain silent as far
as ferroelectricity is concerned
Large-scale collective motion of RFGC galaxies
We processed the data about radial velocities and HI linewidths for 1678 flat
edge-on spirals from the Revised Flat Galaxy Catalogue. We obtained the
parameters of the multipole components of large-scale velocity field of
collective non-Hubble galaxy motion as well as the parameters of the
generalized Tully-Fisher relationship in the "HI line width - linear diameter"
version. All the calculations were performed independently in the framework of
three models, where the multipole decomposition of the galaxy velocity field
was limited to a dipole, quadrupole and octopole terms respectively. We showed
that both the quadrupole and the octopole components are statistically
significant.
On the basis of the compiled list of peculiar velocities of 1623 galaxies we
obtained the estimations of cosmological parameters Omega_m and sigma_8. This
estimation is obtained in both graphical form and as a constraint of the value
S_8=sigma_8(Omega_m/0.3)^0.35 = 0.91 +/- 0.05.Comment: Accepted for publication in Astrophysics and Space Scienc
Accretion and ejection in black-hole X-ray transients
Aims: We summarize the current observational picture of the outbursts of
black-hole X-ray transients (BHTs), based on the evolution traced in a
hardness-luminosity diagram (HLD), and we offer a physical interpretation.
Methods: The basic ingredient in our interpretation is the Poynting-Robertson
Cosmic Battery (PRCB, Contopoulos & Kazanas 1998), which provides locally the
poloidal magnetic field needed for the ejection of the jet. In addition, we
make two assumptions, easily justifiable. The first is that the mass-accretion
rate to the black hole in a BHT outburst has a generic bell-shaped form. This
is guaranteed by the observational fact that all BHTs start their outburst and
end it at the quiescent state. The second assumption is that at low accretion
rates the accretion flow is geometrically thick, ADAF-like, while at high
accretion rates it is geometrically thin.
Results: Both, at the beginning and the end of an outburst, the PRCB
establishes a strong poloidal magnetic field in the ADAF-like part of the
accretion flow, and this explains naturally why a jet is always present in the
right part of the HLD. In the left part of the HLD, the accretion flow is in
the form of a thin disk, and such a disk cannot sustain a strong poloidal
magnetic filed. Thus, no jet is expected in this part of the HLD. The
counterclockwise traversal of the HLD is explained as follows: the poloidal
magnetic field in the ADAF forces the flow to remain ADAF and the source to
move upwards in the HLD rather than to turn left. Thus, the history of the
system determines the counterclockwise traversal of the HLD. As a result, no
BHT is expected to ever traverse the entire HLD curve in the clockwise
direction.
Conclusions: We offer a physical interpretation of accretion and ejection in
BHTs with only one parameter, the mass transfer rate.Comment: Accepted for publication in A&
DT/T beyond linear theory
The major contribution to the anisotropy of the temperature of the Cosmic
Microwave Background (CMB) radiation is believed to come from the interaction
of linear density perturbations with the radiation previous to the decoupling
time. Assuming a standard thermal history for the gas after recombination, only
the gravitational field produced by the linear density perturbations present on
a universe can generate anisotropies at low z (these
anisotropies would manifest on large angular scales). However, secondary
anisotropies are inevitably produced during the nonlinear evolution of matter
at late times even in a universe with a standard thermal history. Two effects
associated to this nonlinear phase can give rise to new anisotropies: the
time-varying gravitational potential of nonlinear structures (Rees-Sciama RS
effect) and the inverse Compton scattering of the microwave photons with hot
electrons in clusters of galaxies (Sunyaev-Zeldovich SZ effect). These two
effects can produce distinct imprints on the CMB temperature anisotropy. We
discuss the amplitude of the anisotropies expected and the relevant angular
scales in different cosmological scenarios. Future sensitive experiments will
be able to probe the CMB anisotropies beyong the first order primary
contribution.Comment: plain tex, 16 pages, 3 figures. Proceedings of the Laredo Advance
School on Astrophysics "The universe at high-z, large-scale structure and the
cosmic microwave background". To be publised by Springer-Verla
Charged-Particle Multiplicities in Charged-Current Neutrino-- and Anti-Neutrino--Nucleus Interactions
The CHORUS experiment, designed to search for
oscillations, consists of a nuclear emulsion target and electronic detectors.
In this paper, results on the production of charged particles in a small sample
of charged-current neutrino-- and anti-neutrino--nucleus interactions at high
energy are presented. For each event, the emission angle and the ionization
features of the charged particles produced in the interaction are recorded,
while the standard kinematic variables are reconstructed using the electronic
detectors. The average multiplicities for charged tracks, the pseudo-rapidity
distributions, the dispersion in the multiplicity of charged particles and the
KNO scaling are studied in different kinematical regions. A study of
quasi-elastic topologies performed for the first time in nuclear emulsions is
also reported. The results are presented in a form suitable for use in the
validation of Monte Carlo generators of neutrino--nucleus interactions.Comment: 17 pages, 5 figure
Whole genome sequencing and progress toward full inbreeding of the mouse collaborative cross population
Two key features of recombinant inbred panels are well-characterized genomes and reproducibility. Here we report on the sequenced genomes of six additional Collaborative Cross (CC) strains and on inbreeding progress of 72 CC strains. We have previously reported on the sequences of 69 CC strains that were publicly available, bringing the total of CC strains with whole genome sequence up to 75. The sequencing of these six CC strains updates the efforts toward inbreeding undertaken by the UNC Systems Genetics Core. The timing reflects our competing mandates to release to the public as many CC strains as possible while achieving an acceptable level of inbreeding. The new six strains have a higher than average founder contribution from non-domesticus strains than the previously released CC strains. Five of the six strains also have high residual heterozygosity (.14%), which may be related to non-domesticus founder contributions. Finally, we report on updated estimates on residual heterozygosity across the entire CC population using a novel, simple and cost effective genotyping platform on three mice from each strain. We observe a reduction in residual heterozygosity across all previously released CC strains. We discuss the optimal use of different genetic resources available for the CC population
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
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