1,395 research outputs found
The stability and melting of aragonite: An experimental and thermodynamic model for carbonated eclogites in the mantle
Subduction of calcium carbonate, sequestered in the oceanic crust by hydrothermal metamorphism and biogenic action, accounts for a significant flux of carbon into the mantle, where it contributes to the genesis of carbonatitic and silica-undersaturated melts. However, the reported phase relations in the system CaCO3, notably the transition boundary from disordered calcite (calcite V, here ccv) to aragonite (ara), vary considerably among different studies. Moreover, the thermodynamic properties of ccv and of liquid CaCO3 (CaCO3L) remain to be determined. In order to address the dearth of experimental data on phase relations, and to determine a set of internally consistent thermodynamic properties for ara, ccv and CaCO3L, multi-anvil experiments were performed at 3\u20136 GPa and 1300\u20131750 \ub0C. By re-evaluating all experimental data, the transformation of ccv-ara fits the equation Tccv-ara = 397.6 + 320.17
7 P and the melting curve Tm = 1578.9 + 139.65
7 P 12 11.646
7 P2, where pressure is in GPa and temperature in K. Thermodynamic properties retrieved for calcite V and liquid CaCO3 are used to compute phase diagrams of relevance for chemical compositions representative of eclogite heterogeneities of the astenospheric mantle, and compared with experimentally derived phase relationships. Aragonite represents a carbonate of major abundance in carbonated eclogites at high temperature, close to the solidus; its ability to fractionate REE and Ba-Sr contributes to the peculiar geochemical signatures of silica undersaturated magmas. The relatively refractory nature of aragonite impacts on our understanding of the deep carbon cycle
Biomarkers of aging in HIV: inflammation and the microbiome
Purpose: HIV-infected subjects present increased levels of inflammatory cytokines and T cell activation in the peripheral blood despite suppressive combination antiretroviral therapy which renders them susceptible to premature aging. The purpose of the present work was to review existing evidence on the ways in which the anatomical and microbiological abnormalities of the gastrointestinal tract can represent a major cause of organ disease in HIV infection. Methods: We conducted a systematic review of the Pubmed database for articles published from 2014 to 2018. We included studies on inflammatory/activation biomarkers associated with cardiovascular and bone disease, neurocognitive impairment and serious non-AIDS events in HIV-infected subjects. We also included researches which linked peripheral inflammation/activation to the anatomical, immune and microbiological alterations of the gastrointestinal tract. Results: Recent literature data confirm the association between non-infectious comorbidities and inflammation in HIV infection which may be driven by gastrointestinal tract abnormalities, specifically microbial translocation and dysbiosis. Furthermore, there is mounting evidence on the possible role of metabolic functions of the microbiota in the pathogenesis of premature aging in the HIV-infected population. Conclusions: Biomarkers need to be validated for their use in the management of HIV infection. Compounds which counteract microbial translocation, inflammation and dysbiosis have been investigated as alternative therapeutic strategies in viro-suppressed HIV-infected individuals, but appear to have limited efficacy, probably due to the multifactorial pathogenesis of non-infectious comorbidities in this setting
Short-Term Repeated-Sprint Training (Straight Sprint vs. Changes of Direction) in Soccer Players
Repeated-sprint training (RST) is considered a critical training method in team sports. It is well known that RST effects may depend on several variables such as the duration of the protocol and repeated-sprint methodology. Few studies have evaluated very short-term protocols and compared different RST modalities. The aim of this study was to compare the effectiveness of 2 week RST including straight sprints or changes of direction (CODs) on physical performance in a sample of soccer players. This study used a randomised pre-post parallel group trial design. The participants were assigned to either an RST group using straight sprints (RST-SS = 18 players) or an RST group using CODs (RST-COD = 18 players). The protocols were: 3 sets of 7 x 30 m sprints for the RST-SS and 7 x 20 + 20 m (one COD of 180 degrees) for the RST-COD, with 20 s and 4 min recovery between sprints and sets, respectively. The following evaluations were performed: 10 and 20 m sprint, agility test, repeated sprint test (RSTbest and RSTmean), and Yo-Yo Recovery Level 1. After the training period, the RST-SS did not report any performance variation, while the RST-COD showed improvements in the 10 m sprint and RSTbest (effect size = 0.70 and 0.65, respectively). The between-group analysis did not report any statistical difference between the RST-SS and the RST-COD. In conclusion, this study did not support the utilisation of a very short-term RST protocol with soccer players, however, the RST-COD presented some additional benefits in sprint performance compared to the RST-SS
Hopping on the Bethe lattice: Exact results for densities of states and dynamical mean-field theory
We derive an operator identity which relates tight-binding Hamiltonians with
arbitrary hopping on the Bethe lattice to the Hamiltonian with nearest-neighbor
hopping. This provides an exact expression for the density of states (DOS) of a
non-interacting quantum-mechanical particle for any hopping. We present
analytic results for the DOS corresponding to hopping between nearest and
next-nearest neighbors, and also for exponentially decreasing hopping
amplitudes. Conversely it is possible to construct a hopping Hamiltonian on the
Bethe lattice for any given DOS. These methods are based only on the so-called
distance regularity of the infinite Bethe lattice, and not on the absence of
loops. Results are also obtained for the triangular Husimi cactus, a recursive
lattice with loops. Furthermore we derive the exact self-consistency equations
arising in the context of dynamical mean-field theory, which serve as a
starting point for studies of Hubbard-type models with frustration.Comment: 14 pages, 9 figures; introduction expanded, references added;
published versio
Magnetic and Combined Field Integral Equations Based on the Quasi-Helmholtz Projectors
Boundary integral equation methods for analyzing electromagnetic scattering phenomena typically suffer from several of the following shortcomings: 1) ill-conditioning when the frequency is low; 2) ill-conditioning when the discretization density is high; 3) ill-conditioning when the structure contains global loops (which are computationally expensive to detect); 4) incorrect solution at low frequencies due to a loss of significant digits; and 5) the presence of spurious resonances. In this article, quasi-Helmholtz projectors are leveraged to obtain magnetic field integral equation (MFIE) that is immune to drawbacks 1)-4). Moreover, when this new MFIE is combined with a regularized electric field integral equation (EFIE), a new quasi-Helmholtz projector-combined field integral equation (CFIE) is obtained that also is immune to 5). The numerical results corroborate the theory and show the practical impact of the newly proposed formulations
Synchrotron radiation μ X-ray diffraction in transmission geometry for investigating the penetration depth of conservation treatments on cultural heritage stone materials
The assessment of the penetration depth of conservation treatments applied to cultural heritage stone
materials is a burning issue in conservation science. Several analytical approaches have been proposed
but, at present, many of them are not fully exhaustive to define in a direct way the composition and
location of the conservation products formed after inorganic mineral treatments. Here, we explored, for
the first time, the analytical capability of synchrotron radiation m X-ray diffraction in transmission
geometry (SR-mTXRD) for the study of the crystal chemistry and penetration depth of the consolidating
phases formed after the application of diammonium hydrogen phosphate (DAP) treatments on a porous
carbonatic stone (Noto limestone). The SR-mTXRD approach provided unambiguous information on the
nature of the newly formed calcium phosphates (hydroxyapatite, HAP, and octacalcium phosphate, OCP)
with depth, supplying important indications of the diffusion mechanism and the reactivity of the
substrate. Qualitative and semi-quantitative data were obtained at the microscale with a non-destructive
protocol and an outstanding signal-to-noise ratio. The SR-mTXRD approach opens a new analytical
scenario for the investigation of a wide range of cultural heritage materials, including natural and artificial
stone materials, painted stratigraphies, metals, glasses and their decay products. Furthermore, it can
potentially be used to characterize the penetration depth of a phase \u201cA\u201d (or more crystalline phases) in
a matrix \u201cB\u201d also beyond the cultural heritage field, demonstrating the potential wide impact of the study
On a Calder\'on preconditioner for the symmetric formulation of the electroencephalography forward problem without barycentric refinements
We present a Calder\'on preconditioning scheme for the symmetric formulation
of the forward electroencephalographic (EEG) problem that cures both the dense
discretization and the high-contrast breakdown. Unlike existing Calder\'on
schemes presented for the EEG problem, it is refinement-free, that is, the
electrostatic integral operators are not discretized with basis functions
defined on the barycentrically-refined dual mesh. In fact, in the
preconditioner, we reuse the original system matrix thus reducing computational
burden. Moreover, the proposed formulation gives rise to a symmetric,
positive-definite system of linear equations, which allows the application of
the conjugate gradient method, an iterative method that exhibits a smaller
computational cost compared to other Krylov subspace methods applicable to
non-symmetric problems. Numerical results corroborate the theoretical analysis
and attest of the efficacy of the proposed preconditioning technique on both
canonical and realistic scenarios
On some Operator Filtering Strategies Based on Suitably Modified Green's Functions
Recent contributions showed the benefits of operator filtering for both
preconditioning and fast solution strategies. While previous contributions
leveraged laplacian-based filters, in this work we introduce and study a
different approach leveraging the truncation of appropriately chosen spectral
representations of operators' kernels. In this contribution, the technique is
applied to the operators of the 2D TE- and TM-electric field integral equations
(EFIE). We explore two different spectral representations for the 2D Green's
function that lead to two distinct types of filtering of the EFIE operators.
Numerical results corroborate the effectiveness of the newly proposed
approaches, also in the Calder\'on preconditioned EFIEComment: 3 pages, 3 figures, to be published in ICEAA 202
- …