Search results for "DISPERSION"
showing 10 items of 1101 documents
Cleaning sorbents used in matrix solid-phase dispersion with sonication: Application to the estimation of polycyclic aromatic hydrocarbons at ng/g le…
2012
This study shows that ultrasonic assisted extraction is a good practise for removing impurities from sorbents used for matrix-solid phase dispersion (MSPD). A previous washing of the sorbent with an organic solvent or mixture of solvents eliminates part of the interferences, but this treatment is not enough for the quantification of PAHs at ng/g levels. It is demonstrated that the determination of traces of polycyclic aromatic hydrocarbons (PAHs) in solid samples processed by matrix-solid phase dispersion (MSPD) may be severely affected by the presence of sorbent impurities. Different extraction solvents and sonication conditions have been tested, and on the basis of the results obtained a …
Dispersion Interaction between Two Hydrogen Atoms in a Static Electric Field
2019
We consider the dispersion interaction between two ground-state hydrogen atoms, interacting with the quantum electromagnetic field in the vacuum state, in the presence of an external static electric field, both in the nonretarded and in the retarded Casimir-Polder regime. We show that the presence of the external field strongly modifies the dispersion interaction between the atoms, changing its space dependence. Moreover, we find that, for specific geometrical configurations of the two atoms with respect to the external field and/or the relative orientation of the fields acting on the two atoms, it is possible to change the character of the dispersion force, turning it from attractive to re…
Massless positivity in graviton exchange
2021
We formulate Positivity Bounds for scattering amplitudes including exchange of massless particles. We generalize the standard construction through dispersion relations to include the presence of a branch cut along the real axis in the complex plane for the Maldestam variable $s$. In general, validity of these bounds require the cancellation of divergences in the forward limit of the amplitude, proportional to $t^{-1}$ and $\log(t)$. We show that this is possible in the case of gravitons if one assumes a Regge behavior of the amplitude at high energies below the Planck scale, as previously suggested in the literature, and that the concrete UV behaviour of the amplitude is uniquely determined…
The QCD analytic effective charge and its dependence on the pion mass
2004
A new model for the QCD analytic running coupling, which incorporates the effects due to the $\pi$ meson mass, is proposed. The properties of this invariant charge in spacelike and timelike regions are examined. Its main distinctive features are a finite infrared limiting value, which depends on the pion mass, and the "plateau-like" behavior in the deep infrared domain of the timelike region.
A novel integral representation for the Adler function
2005
New integral representations for the Adler D-function and the R-ratio of the electron-positron annihilation into hadrons are derived in the general framework of the analytic approach to QCD. These representations capture the nonperturbative information encoded in the dispersion relation for the D-function, the effects due to the interrelation between spacelike and timelike domains, and the effects due to the nonvanishing pion mass. The latter plays a crucial role in this analysis, forcing the Adler function to vanish in the infrared limit. Within the developed approach the D-function is calculated by employing its perturbative approximation as the only additional input. The obtained result …
Distribution of relaxation times in 0.5PMN-0.5PSN ceramics
2007
Dielectric properties of chemically ordered and disordered 0.5PbMg1/3Nb2/3O3-0.5 PbSc1/2Nb1/2O3 (0.5PMN-0.5PSN) ceramics were investigated in frequency range from 20 Hz to 3 GHz by dielectric spectroscopy. The broad dielectric dispersion, similar to this typically obtained for relaxor ferroelectrics (RFE), was observed in both ceramics below 350 K. The frequency dependence of dielectric permittivity of these ceramics were analyzed in terms of the distribution of relaxation times and showed the splitting into two components at lower temperatures. The longest relaxation times part slows down following Vogel-Fulcher law with lower freezing temperature compare with typical RFE like PbMg1/3Nb2/3…
Acoustic properties of nanoscale oxide heterostructures probed by UV Raman spectroscopy
2007
We study high quality molecular-beam epitaxy grown BaTiO3/SrTiO3 superlat-tices using ultraviolet Raman spectroscopy. In the low energy spectral region, acoustic phonon doublets are observed. These are due to the artificial superlattice periodicity and consequent folding of the acoustic phonon dispersion. From the study of samples with different BaTiO3/SrTiO3 layer thicknesses the effective sound velocities within each of the layers are obtained.
High-pressure study of the aurophilic topological Dirac material AuI
2022
We endeavour to explore the high-pressure study in the aurophilic AuI within the state-of-the-art of first principles. The impediment of expressing precise ground-state features of aurophilic compounds that had afflicted prior theoretical research has been resolved by incorporating van der Waals corrections (vdw). Mechanical and dynamical stability are ensured at ambient using the computed elastic constants and phonon dispersion curves. The dynamical instability is triggered by the application of pressure in AuI, as evidenced by the softening of an acoustic mode (Eu) at ∼7 GPa. Non-adherence of estimated elastic constants to the Born stability criterion at this pressure illustrates the syst…
Interpreting and modelling field data for wastewater dispersion into sea trough dimensional analysis
2008
This paper deals with the mathematical and experimental characterization of a coastal urban wastewater discharge in the South Tyrrhenian Sea, namely the Golfo di Palermo, western Sicily (Italy). The stretch of water lying before the central part of the capital town receives the wastewater originating from about 200 000 inhabitants. The sewage is currently still discharged on-shore without any prior treatment by a free-surface outfall called “Porta Felice”. The Municipality is currently implementing a plan to connect the sewerage system of these areas to the main wastewater treatment plant; at the moment, however, no mitigation measure has been applied yet and the quality of the Gulf is stil…
Structure and Stability of Racemic and Enantiopure Pimobendan Monohydrates: On the Phenomenon of Unusually High Stability
2017
Study of structures and physicochemical properties of racemic (rac-H) and enantiopure (enant-H) hydrates of the active pharmaceutical ingredient pimobendan revealed that both hydrates have highly similar crystal structures and exhibit unusually high stability. Both structures contain identical two-dimensional layers and very similar conformations. The most significant difference is the stacking of these layers. The high stability of both hydrates appeared as extremely low solubility over a wide temperature range as well as an exceptionally high dehydration temperature and melting point. Study of the dehydration process showed that both hydrates have different activation energies of dehydrat…