273 research outputs found
From Beggars To Citizens: The Right To Nondiscrimination In Admission Into Commercial Establishments In Guatemala
The denial of access to individuals into commercial establishments for arbitrary reasons is a common occurrence
Application of Thermal Response Measurements to Investigate Enhanced Water Adsorption Kinetics in Ball-Milled C2N-Type Materials
Sorption-based water capture is an attractive solution to provide potable water in arid regions. Heteroatom-decorated microporous carbons with hydrophilic character are promising candidates for water adsorption at low humidity, but the strong affinity between the polar carbon pore walls and water molecules can hinder the water transport within the narrow pore system. To reduce the limitations of mass transfer, C2N-type carbon materials obtained from the thermal condensation of a molecular hexaazatriphenylene-hexacarbonitrile (HAT-CN) precursor were treated mechanochemically via ball milling. Scanning electron microscopy as well as static light scattering reveal that large pristine C2N-type particles were split up to a smaller size after ball milling, thus increasing the pore accessibility which consequently leads to faster occupation of the water vapor adsorption sites. The major aim of this work is to demonstrate the applicability of thermal response measurements to track these enhanced kinetics of water adsorption. The adsorption rate constant of a C2N material condensed at 700 °C remarkably increased from 0.026 sâ1 to 0.036 sâ1 upon ball milling, while maintaining remarkably high water vapor capacity. This work confirms the advantages of small particle sizes in ultramicroporous materials on their vapor adsorption kinetics. It is demonstrated that thermal response measurements are a valuable and time-saving method to investigate water adsorption kinetics, capacities, and cycling stability
Relativistic RPA plus phonon-coupling analysis of pygmy dipole resonances
The relativistic random-phase approximation (RRPA) plus phonon-coupling (PC)
model is applied in the analysis of E1 strength distributions in Pb and
Sn, for which data on pygmy dipole resonances (PDR) have recently been
reported. The covariant response theory is fully consistent: the effective
nuclear interaction NL3 is used both to determine the spectrum of
single-nucleon Dirac states, and as the residual interaction which determines
the collective phonon states in the relativistic RPA. It is shown that the
picture of the PDR as a resonant oscillation of the neutron skin against the
isospin saturated proton-neutron core, and with the corresponding RRPA state
characterized by a coherent superposition of many neutron particle-hole
configurations, remains essentially unchanged when particle-vibration coupling
is included. The effect of two-phonon admixtures is a weak fragmentation and a
small shift of PDR states to lower excitation energy. Even though the PDR
calculated in the extended model space of phonon configurations
contains sizeable two-phonon admixtures, it basically retains a one-phonon
character and its dynamics is not modified by the coupling to low-lying surface
vibrations.Comment: 17 pages, 3 figures, 4 table
Probing the Nuclear Neutron Skin by Low-Energy Dipole Modes
Dipole excitations below the neutron threshold in neutron rich Sn isotopes
are studied theoretically in the Quasiparticle-Phonon Model with HFB single
particle input. Of special interest are the low-lying two-phonon 1- states and
the Pygmy Dipole Resonance (PDR). The evolution of low-energy dipole
excitations with neutron excess is investigated over the Sn isotopic chain
including the experimentally unknown regions close to 132Sn. A dependence of
the PDR strengths and centroid energies on the neutron skin thickness is found.
Despite significant multi-phonon contributions to mean energies and transition
strengths, the PDR states retain their one-phonon character. The fragmentation
pattern is reduced with increasing neutron excess towards the N=82 shell
closure which will be of advantage for future experimental work.Comment: 4 pages, 2 figure
A cluster version of the GGT sum rule
We discuss the derivation of a ``cluster sum rule'' from the
Gellmann-Goldberger-Thirring (GGT) sum rule as an alternative to the
Thomas-Reiche-Kuhn (TRK) sum rule, which was used as the basis up to now. We
compare differences in the assumptions and approximations. Some applications of
the sum rule for halo nuclei, as well as, nuclei with a pronounced cluster
structure are discussed.Comment: 14 pages, to be published in Nucl. Phys.
Spin-orbit splitting and the tensor component of the Skyrme interaction
We study the role of the tensor term of the Skyrme effective interactions on
the spin-orbit splittings in the N=82 isotones and Z=50 isotopes. The different
role of the triplet-even and triplet-odd tensor forces is pointed out by
analyzing the spin-orbit splittings in these nuclei. The experimental isospin
dependence of these splittings cannot be described by Hartree-Fock calculations
employing the usual Skyrme parametrizations, but is very well accounted for
when the tensor interaction is introduced. The capability of the Skyrme forces
to reproduce binding energies and charge radii in heavy nuclei is not destroyed
by the introduction of the tensor term. Finally, we also discuss the effect of
the tensor force on the centroid of the Gamow-Teller states.Comment: Submitted to Phys. Lett.
Giant resonances in exotic spherical nuclei within the RPA approach with the Gogny force
Theoretical results for giant resonances in the three doubly magic exotic
nuclei Ni, Sn and Sn are obtained from Hartree-Fock (HF)
plus Random Phase Approximation (RPA) calculations using the D1S
parametrization of the Gogny two-body effective interaction. Special attention
is paid to full consistency between the HF field and the RPA particle-hole
residual interaction. The results for the exotic nuclei, on average, appear
similar to those of stable ones, especially for quadrupole and octupole states.
More exotic systems have to be studied in order to confirm such a trend. The
low energy of the monopole resonance in Ni suggests that the compression
modulus in this neutron rich nucleus is lower than the one of stable ones.Comment: 16 pages, 10 figure
Improving the Stability of Supercapacitors at High Voltages and High Temperatures by the Implementation of Ethyl Isopropyl Sulfone as Electrolyte Solvent
Abstract Two of the main weaknesses of modern electric doubleâlayer capacitors are the rather limited ranges of operating voltage and temperature in which these devices do not suffer from the occurrence of irreversible decomposition processes. These parameters are strongly interconnected and lowering the operating voltage when increasing the temperature is unavoidable, so as to protect the electric doubleâlayer capacitor from damage. With the aim to maintain the operating voltage as high as possible at elevated temperatures, in this study, the application of ethyl isopropyl sulfone as an electrolyte solvent for electric doubleâlayer capacitors is presented. It is shown that ethyl isopropyl sulfoneâbased electrolytes display excellent thermal and electrochemical stability enabling high capacitance retention after floating tests for 500 h at 60 and 80 °C, e.g. 68% at 3.4 V at 60 °C. A possible reason for the aboveâaverage stability is that decomposition products of ethyl isopropyl sulfone can deposit on the electrode surface which may act as a passivation layer and prevent further degradation.Ethyl isopropyl sulfone is an interesting electrolyte solvent for electric doubleâlayer capacitors in highâtemperature surroundings. Forming a protective passive layer on the electrode surface, ethyl isopropyl sulfone offers high thermal and electrochemical stability for supercapacitors at temperatures of up to 80 °C and voltages of up to 3.4 V. imag
Nuclear vorticity and the low-energy nuclear response - Towards the neutron drip line
The transition density and current provide valuable insight into the nature
of nuclear vibrations. Nuclear vorticity is a quantity related to the
transverse transition current. In this work, we study the evolution of the
strength distribution, related to density fluctuations, and the vorticity
strength distribution, as the neutron drip line is approached. Our results on
the isoscalar, natural-parity multipole response of Ni isotopes, obtained by
using a self-consistent Skyrme-Hartree-Fock + Continuum RPA model, indicate
that, close to the drip line, the low-energy response is dominated by L>1
vortical transitions.Comment: 8 pages, incl. 4 figures; to appear in Phys.Lett.
Low-energy dipole excitations towards the proton drip-line: doubly magic 48Ni
The properties of the low-energy dipole response are investigated for the
proton-rich doubly magic nucleus Ni, in a comparative study of two
microscopic models: fully self-consistent Relativistic Random-Phase
Approximation(RRPA) based on the novel density-dependent meson-exchange
interactions, and Continuum Random-Phase Approximation(CRPA) using Skyrme-type
interactions with the continuum properly included. Both models predict the
existence of the low-energy soft mode, i.e. the proton pygmy dipole resonance
(PDR), for which the transition densities and RPA amplitudes indicate the
dynamics of loosely bound protons vibrating against the rest of the nucleons.
The CRPA analysis indicates that the escape width for the proton PDR is rather
large, as a result of the coupling to the continuum.Comment: 12 pages, 3 figures, accepted for publication in Phys. Lett.
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