1,461 research outputs found
Lanthanides in granulometric fractions of Mediterranean soils. Can they be used as fingerprints of provenance?
Highlights
Are lanthanides from fine sand and clay genetically related to the geological materials?
Lanthanide concentrations of fine sand and clay fit chronofunctions
Pearson's r of lanthanide couples decreases when separation increases in the periodic table
Free forms of clay are scavengers of lanthanides and concentrate HREE and ceriumSample preparation and chemical analysis were conducted by
Emma Humphreys-Williams and Stanislav Strekopytov (Imaging
and Analysis Centre, Natural History Museum, London, UK). This
work was supported by a grant from Ministerio de EconomĂa, Industria y Competitividad de España (âTipologĂas de Suelos MediterrĂĄneos versus Cuarzo. En la frontera del conocimiento edafogenĂ©ticoâ; Ref. CGL2016-80308-P). The authors thank Professor
Margaret A. Oliver, an anonymous editor and two anonymous
reviewers for helpful comments and suggestions that improved the
final manuscript. We also thank Robert Abrahams (Bsc) for revising
the English language.There is geochemical interest in the lanthanides because they behave like a group that is closely related to the parent materials during surface processes, although they also undergo fractionation as a result of supergene dynamics. We analysed lanthanide concentrations (ICPms) in the granulometric fractions fine sand, clay and free forms of clay (FFclayâCDB and FFclayâOx: extracted with citrateâdithioniteâsodium bicarbonate and with ammonium oxalate, respectively) from a soil chronosequence of Mediterranean soils. There was a relative enrichment of heavy rare earth elements (HREE) in the clay fraction and its free forms with respect to fine sand. The clay free forms behaved as scavengers of lanthanides, and oxidative scavenging of cerium (Ce) in FFclayâCDB was also detected. Lanthanide concentrations (lanthanum to gadolinium in fine sand; terbium to lutetium in clay) varied with soil age, and chronofunctions were established. There was a strong positive collinearity between most of the lanthanide concentrations. Furthermore, the value of the correlation index (Pearson's r ) of the concentrations between couples of lanthanides (r CLC) decreased significantly with increasing separation between the elements in the periodic table; this has never been described in soils. Several geochemical properties and indices in the fine sand and clay soil fractions and in the geological materials of the Guadalquivir catchment showed, on the one hand, a genetic relation between them all, enabling the lanthanides to be used as fingerprints of provenance; on the other hand, fractionation between fine sand and clay showed these are actively involved in soil lanthanide dynamics.SecretarĂa de Estado de InvestigaciĂłn, Desarrollo e InnovaciĂłn. Grant Number: CGL2016â80308â
Time resolved scattering relaxation mechanisms of microcavity polaritons
We study the polariton relaxation dynamics for different scattering
mechanisms as: Phonon and electron scattering procesess. The relaxation
polariton is obtained at very short times by solving the Boltzman equation.
Instead of the well-known relaxation process by phonons, we show that the
bottleneck effect relaxes to the ground state more efficiently at low pump
power intensity when the electron relaxation process is included. In this way,
we clearly demonstrate that different relaxation times exist, for which any of
these two mechanism is more efficient to relax the polariton population to the
ground state.Comment: 10 eps figure
Free Energy of a Dilute Bose Gas: Lower Bound
A lower bound is derived on the free energy (per unit volume) of a
homogeneous Bose gas at density and temperature . In the dilute
regime, i.e., when , where denotes the scattering length of
the pair-interaction potential, our bound differs to leading order from the
expression for non-interacting particles by the term . Here, denotes the critical density for
Bose-Einstein condensation (for the non-interacting gas), and denotes
the positive part. Our bound is uniform in the temperature up to temperatures
of the order of the critical temperature, i.e., or smaller.
One of the key ingredients in the proof is the use of coherent states to extend
the method introduced in [arXiv:math-ph/0601051] for estimating correlations to
temperatures below the critical one.Comment: LaTeX2e, 53 page
On the microstructure and mechanical properties of an Fe-10Ni-7Mn martensitic steel processed by high-pressure torsion.
High-pressure torsion (HPT) processing was applied to an Fe-10Ni-7Mn (wt.%) martensitic steel at room temperature and the grain size was reduced from an initial value of ~5.5 ÎŒm to an ultrafine value of ~185 nm for the ferritic phase and around 30 nm for the austenitic phase after 20 HPT turns. The microstructure and mechanical properties of the as-processed material were evaluated using X-ray diffraction (XRD), electron backscatter diffraction (EBSD), field emission scanning electron microscopy (FESEM), microhardness measurements and tensile testing. In addition, annealing of an as-processed specimen was analyzed by differential scanning calorimetry (DSC). The results show that HPT processing increases the hardness and ultimate tensile strength to ~690 Hv and ~2230 MPa, respectively, but the ductility is decreased from ~16.5% initially to ~6.4% and ~3.1% after 10 and 20 turns, respectively. The hardness distributions and EBSD images show that a reasonably homogeneous microstructure is formed when applying a sufficient level of pressure and torsional strain. The DSC results demonstrate that processing by HPT reduces the start and finish temperatures of the reverse transformation of martensite to austenite and there is continuous re-crystallization after the recovery process
CP violation in in the model III 2HDM
We have calculated the Wilson coefficients (i=1,2) in the
renormalization scheme in the model III 2HDM. Using the obtained
Wilson coefficients, we have analyzed the CP violation in decays (q=d,s) in the model. The CP asymmetry, , depends on the
parameters of models and in can be as large as 40% and
35% for and respectively. It can reach 4% for decays.
Because in SM CP violation is smaller than or equal to O() which is
unobservably small, an observation of CP asymmetry in the decays would unambiguously signal the existence of new physics.Comment: revtex4, 16 pages, 7 figure
Longitudinal polarization asymmetry of leptons in the pure leptonic B decays
Longitudinal lepton polarization asymmetry in B_q -> l l (q = d, s$ and l =
e, mu, tau) decays is investigated. The analysis is done in a general manner by
using the effective operators approach. It is shown that the longitudinal
lepton polarization asymmetry would provide a direct search for the scalar and
pseudoscalar type interactions, which are induced in all variants of
Higgs-doublet models.Comment: 7 page
Determination of the and Mixing Angle from the Pseudoscalar Transition Form Factors
The possible range of mixing angle is determined from the
transition form factors and with
the help of the present experimental data. For such purpose, the quark-flavor
mixing scheme is adopted and the pseudoscalar transition form factors are
calculated under the light-cone pQCD framework, where the transverse momentum
corrections and the contributions beyond the leading Fock state have been
carefully taken into consideration. We construct a phenomenological expression
to estimate the contributions to the form factors beyond the leading Fock state
based on their asymptotic behavior at and . By taking
the quark-flavor mixing scheme, our results lead to , where the first error coming from experimental
uncertainty and the second error coming from the uncertainties of the
wavefunction parameters. The possible intrinsic charm component in and
is discussed and our present analysis also disfavors a large portion of
intrinsic charm component in and , e.g. .Comment: 18 Pages, 3 figures. Several references added. To be published in
EPJ
Light localization in quasi-periodic nano-photonics carpets
In this work we show the formation of quasi-periodic field carpets and strong localization of light in the proximity of a planar quasi-crystal array of nano-holes in metallic screen
Bounded version vectors
Version vectors play a central role in update tracking under optimistic distributed systems, allowing the detection of obsolete or inconsistent versions of replicated data. Version vectors do not have a bounded representation; they are based on integer counters that grow indefinitely as updates occur. Existing approaches to this problem are scarce; the mechanisms proposed are either unbounded or operate only under specific settings. This paper examines version vectors as a mechanism for data causality tracking and clarifies their role with respect to vector clocks. Then, it introduces bounded stamps and proves them to be a correct alternative to integer counters in version vectors. The resulting mechanism, bounded version vectors, represents the first bounded solution to data causality tracking between replicas subject to local updates and pairwise symmetrical synchronization.FCT project POSI/ICHS/44304/2002, FCT under grant BSAB/390/2003
Interpretation of computational thinking evaluation results for enrollment prediction
During two generations (2016 and 2017) the computational
thinking evaluation has been carried out in order to establish
learning scenarios for new students, such interventions have been
made in the Programming methodology course, it belonging to
the career of Information Technology at the Technological
University of Puebla in MĂ©xico. The results have led a personalized
education for students, recognizing previous skills as well as
trying to correct those missing, so that it acquires the
competences respective, credit the course and improve the
retention percentage of the first quarter. In this sense, when
detecting possible skill gaps, is it possible to predict what will be
the impact to maintain or decrease enrollment during and the end
of quarter? The present work aims to answer the question by the
results interpretation obtained from the computational thinking
evaluation to 242 new students, generation 2018. Initially, it was
stablished which would be the student's situation during and the
end of four months from September to December based on the
correct assessment reagents; three categories were determined: 1.
Sure desertion, 2. Safe permanence, 3. Variable permanence. Later,
50 students who enrolled the next quarter (January-April 2019)
were revised if they had been predicted properly; using a survey,
the familiarity of key concepts of the subject Programming
methodology was obtained with the aim of determining a
correspondence with the evaluation of computational thinking
skills, as well as the established situation, consequently,
establishing the validity of predicting the enrollment
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