1,270 research outputs found
How Much Can We Trust Major Element Quantification in Bioapatite Investigation?
Bioapatite is probably the key factor in the unreplicated success of vertebrates. Chemical data on bioapatite composition can be achieved on a solid sample by using different analytical tools such as spectroscopic and spectrometric methods. As analytical outputs can be affected by the physical-chemical characteristics of the sample matrix, an internal standard is usually required to correct and validate the results. Bioapatite lattice can accommodate iso- and heterovalent substitutions during life or diagenesis varying its chemical composition through (geological) time. If on the one hand, this makes bioapatite a unique archive of physical and chemical information for both the living cycle and the events occurring after death, on the other, it excludes the identification of a sole internal standard. Here, we propose a method to measure major element concentration with specific care for P, Ca, Mg, Na, K, Si, Al, and Fe, which are the main substituent atoms in bioapatite, through homemade matrix-matched external calibration standards for laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). We tested the method on living and fossil shark teeth, critically comparing the results obtained using other analytical techniques and certified external standards. We demonstrated that matrix-matched calibration in LA-ICPMS is mandatory for obtaining a reliable chemical characterization even if factors such as matrix aggregation variability, diverse presence of volatile compounds, the fossilization footprint, and the instrumental variability can represent further variability parameters
Capillary penetration method for measuring wetting properties of carbon ionomer films for proton exchange membrane fuel cell (PEMFC) applications
In this work, capillary rise experiments were performed to assess the wetting properties of carbon-ionomer (CI) films. The samples were attached to a micro-balance and then immersed into liquid water to (i) measure the mass gain from the liquid uptake and (ii) estimate the (external) contact angle to water (typical value around 140°). The results showed that drying the CI films under low vacuum significantly impacted the CI film wettability. The influence of the ionomer content on the CI films’ wettability was investigated with various ionomer to carbon (I/C) ratios: 0.8, 1.0, 1.2 and 1.4. No significant variation of the contact angle to water extracted from the capillary rise experiment was measured. However, water uptake increased with the I/C ratio suggesting a more hydrophilic behavior. This observation was in good agreement with the measurement from the sessile drop method showing a slight decrease of the contact angle to water: from 155° for an I/C of 0.8 to 135° for I/C = 1.4
Non-Fermi-liquid phases in the two-band Hubbard model: Finite-temperature exact diagonalization study of Hund's rule coupling
The two-band Hubbard model involving subbands of different widths is
investigated via finite-temperature exact diagonalization (ED) and dynamical
mean field theory (DMFT). In contrast to the quantum Monte Carlo (QMC) method
which at low temperatures includes only Ising-like exchange interactions to
avoid sign problems, ED permits a treatment of Hund's exchange and other onsite
Coulomb interactions on the same footing. The role of finite-size effects
caused by the limited number of bath levels in this scheme is studied by
analyzing the low-frequency behavior of the subband self-energies as a function
of temperature, and by comparing with numerical renormalization group (NRG)
results for an effective one-band model. For half-filled, non-hybridizing
bands, the metallic and insulating phases are separated by an intermediate
mixed phase with an insulating narrow and a bad-metallic wide subband. The wide
band in this phase exhibits different degrees of non-Fermi-liquid behavior,
depending on the treatment of exchange interactions. Whereas for complete
Hund's coupling, infinite lifetime is found at the Fermi level, in the absence
of spin-flip and pair-exchange, this lifetime becomes finite. Excellent
agreement is obtained both with new NRG and previous QMC/DMFT calculations.
These results suggest that-finite temperature ED/DMFT might be a useful scheme
for realistic multi-band materials.Comment: 15 pages, 17 figure
Variation in Normal Range Thyroid Function Affects Serum Cholesterol Levels, Blood Pressure, and Type 2 Diabetes Risk: A Mendelian Randomization Study
Final publication is available from Mary Ann Liebert, Inc., publishers https://doi.org/10.1089/thy.2020.0393
Thermodynamic Stability at the Two-Particle Level
We show how the stability conditions for a system of interacting fermions
that conventionally involve variations of thermodynamic potentials can be
rewritten in terms of local one- and two-particle correlators. We illustrate
the applicability of this alternative formulation in a multi-orbital model of
strongly correlated electrons at finite temperatures, inspecting the lowest
eigenvalues of the generalized local charge susceptibility in proximity of the
phase-separation region. Additionally to the conventional unstable branches, we
address unstable solutions possessing a positive, rather than negative
compressibility. Our stability conditions require no derivative of free energy
functions with conceptual and practical advantages for actual calculations and
offer a clear-cut criterion for analyzing the thermodynamics of correlated
complex systems.Comment: 7 (+6) pages, 4 figure
Advanced European Re-Entry System Based on Inflatable Heat Shields EFESTO project overview: system and mission design and technology roadmap
European Union H2020 EFESTO project is coordinated by DEIMOS Space with the end goals of improving the European TRL of Inflatable Heat Shields for re-entry vehicles from 3 to 4/5 and pave the way to In-Orbit Demonstration that can further raise the TRL to 6. This paper presents the project objectives and provides a general overview of the latest advancements, promoting the relevance of the EFESTO know-how in the frame of a European re-entry technology roadmap. The system, aerodynamic and mission design of two Hypersonic Inflatable Aerodynamic Decelerator use case scenarios, the AVUM VEGA stage recovery and a high-mass Mars exploration EDL mission, have been selected for deriving requirements and constraints to be injected in the EFESTO ground testing phase. The focus of this phase was on the aerothermal verification of the Flexible-Thermal Protection System in the DLR Arcjet facility and the analysis of the mechanical properties of the Inflatable Structure exploiting a manufactured 1:2 demonstrator, both representing key aspects of this peculiar and innovative technology
Orbital-selective Mott transitions: Heavy fermions and beyond
Quantum phase transitions in metals are often accompanied by violations of
Fermi liquid behavior in the quantum critical regime. Particularly fascinating
are transitions beyond the Landau-Ginzburg-Wilson concept of a local order
parameter. The breakdown of the Kondo effect in heavy-fermion metals
constitutes a prime example of such a transition. Here, the strongly correlated
f electrons become localized and disappear from the Fermi surface, implying
that the transition is equivalent to an orbital-selective Mott transition, as
has been discussed for multi-band transition-metal oxides. In this article,
available theoretical descriptions for orbital-selective Mott transitions will
be reviewed, with an emphasis on conceptual aspects like the distinction
between different low-temperature phases and the structure of the global phase
diagram. Selected results for quantum critical properties will be listed as
well. Finally, a brief overview is given on experiments which have been
interpreted in terms of orbital-selective Mott physics.Comment: 29 pages, 4 figs, mini-review prepared for a special issue of JLT
- …