14,109 research outputs found
Properties of nuclear matter from macroscopic-microscopic mass formulas
Based on the standard Skyrme energy density functionals together with the
extended Thomas-Fermi approach, the properties of symmetric and asymmetric
nuclear matter represented in two macroscopic-microscopic mass formulas:
Lublin-Strasbourg nuclear drop energy (LSD) formula and Weizs\"acker-Skyrme
(WS*) formula, are extracted through matching the energy per particle of finite
nuclei. For LSD and WS*, the obtained incompressibility coefficients of
symmetric nuclear matter are MeV and MeV,
respectively. The slope parameter of symmetry energy at saturation density is
MeV for LSD and MeV for WS*, respectively, which
is compatible with the liquid-drop analysis of Lattimer and Lim [ApJ.
\textbf{771}, 51 (2013)]. The density dependence of the mean-field isoscalar
and isovector effective mass, and the neutron-proton effective masses splitting
for neutron matter are simultaneously investigated. The results are generally
consistent with those from the Skyrme Hartree-Fock-Bogoliubov calculations and
nucleon optical potentials, and the standard deviations are large and increase
rapidly with density. A better constraint for the effective mass is helpful to
reduce uncertainties of the depth of the mean-field potential.Comment: 5 figures, to appear in Phys. Lett.
Signal Recognition Particle (SRP) and SRP Receptor: A New Paradigm for Multistate Regulatory GTPases
The GTP-binding proteins or GTPases comprise a superfamily of proteins that provide molecular switches in numerous cellular processes. The “GTPase switch” paradigm, in which a GTPase acts as a bimodal switch that is turned “on” and “off” by external regulatory factors, has been used to interpret the regulatory mechanism of many GTPases for more than two decades. Nevertheless, recent work has unveiled an emerging class of “multistate” regulatory GTPases that do not adhere to this classical paradigm. Instead of relying on external nucleotide exchange factors or GTPase activating proteins to switch between the on and off states, these GTPases have the intrinsic ability to exchange nucleotides and to sense and respond to upstream and downstream factors. In contrast to the bimodal nature of the GTPase switch, these GTPases undergo multiple conformational rearrangements, allowing multiple regulatory points to be built into a complex biological process to ensure the efficiency and fidelity of the pathway. We suggest that these multistate regulatory GTPases are uniquely suited to provide spatial and temporal control of complex cellular pathways that require multiple molecular events to occur in a highly coordinated fashion
Modulating light with light via giant nano-opto-mechanical nonlinearity of plasmonic metamaterial
From the demonstration of saturable absorption by Vavilow and Levshin in
1926, and with invention of the laser, unavailability of strongly nonlinear
materials was a key obstacle for developing optical signal processing, in
particular in transparent telecommunication networks. Today, most advanced
photonic switching materials exploit gain dynamics and near-band and excitonic
effects in semiconductors, nonlinearities in organic media with
weakly-localized electrons and nonlinearities enhanced by hybridization with
metamaterials. Here we report on a new type of artificial nonlinearity that is
nano-opto-mechanical in nature. It was observed in an artificial metamaterial
array of plasmonic meta-molecules supported by a flexible nano-membrane. Here
nonlinearity is underpinned by the reversible reconfiguration of its structure
induced by light. In a film of only 100 nanometres thickness we demonstrated
modulation of light with light using milliwatt power telecom diode lasers.Comment: 6 pages, 5 figure
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