298 research outputs found
Selfconsistent calculations of fission barriers in the Fm region
The fission barriers of the nuclei 254Fm, 256Fm, 258Fm, 258No and 260Rf are
investigated in a fully microscopic way up to the scission point. The analysis
is based on the constrained Hartree-Fock-Bogoliubov theory and Gogny's D1S
force. The quadrupole, octupole and hexadecapole moments as well as the number
of nucleons in the neck region are used as constraints. Two fission paths,
corresponding to the bimodal fission, are found. The decrease with isotope mass
of the half-life times of heavy Fm isotopes is also explained.Comment: 29 pages in LaTeX including 14 figure
Método gráfico de elaboración de los resultados de las experiencias agrícolas : Método de la Hipotenusa
Es cierto que existe una serie de métodos perfeccionados y fáciles para calcular M y m, que proporcionan además la posibilidad de un control intermediario— pero todos estos métodos se refieren al cálculo de los errores medios de gran cantidad de variantes, mientras que en un ensayo de cultivos la cantidad de parcelas, por razones técnicas, es generalmente limitada. Tratando de encontrar un sistema racional para estos cálculos, en su aplicación a las condiciones especiales de las "experimentaciones de variedades", — he logrado obtener un método gráfico especial de la determinación de los errores medios y habiéndolo ensayado sobre el material de la "Experimentación de Variedades" de la zona norte del país, me he convencido de la plena bondad de este método, tanto en lo que se refiere a la suficiente exactitud de las deducciones definitivas obtenidas por este medio, como también por la economía del tiempo introducida por dicho método.Facultad de Ciencias Agrarias y Forestale
Light-particle emission from the fissioning nuclei 126Ba, 188Pt and (266,272,278)/110: theoretical predictions and experimental results
We present a comparison of our model treating fission dynamics in conjunction
with light-particle (n, p, alpha) evaporation with the available experimental
data for the nuclei 126Ba, 188Pt and three isotopes of the element Z=110. The
dynamics of the symmetric fission process is described through the solution of
a classical Langevin equation for a single collective variable characterizing
the nuclear deformation along the fission path. A microscopic approach is used
to evaluate the emission rates for pre-fission light particles.
Entrance-channel effects are taken into account by generating an initial spin
distribution of the compound nucleus formed by the fusion of two deformed
nuclei with different relative orientations
Capacitance, induced charges, and bound states of biased carbon nanotube systems
Although it has long been known that the classical notions of capacitance need modification at the nanoscale, in order to account for important quantum effects, very few first-principles investigations of these properties exist for any real material systems. Here we present the results of a large-scale ab initio investigation of the capacitance properties of carbon nanotube systems. The simulations are based on a recently developed real-space nonequilibrium Green's-function approach, with special attention being paid to the treatment of the bound states present in the system. In addition, use has been made of a symmetry decomposition scheme for the charge density. This is needed both to speed up the calculations and in order to study the origins of the induced charges. Specific systems investigated include two and three nested nanotube shells, the insertion of a capped nanotube into another, a connected (12,0)/(6,6) nanotube junction, and the properties of a nanotube acting as a probe over a flat aluminum surface. First-principles estimates of the capacitance matrix coefficients for all these systems are provided, along with a discussion of the quantum corrections. For the case of the nanotube junction, the numerical value of the capacitance is sufficiently high, as to be useful for future device applications.published_or_final_versio
Collective Quadrupole Excitations in Transitional Nuclei
The generalized Bohr Hamiltonian was used to describe the low-lying collective excitations in even-even isotopes of Ru, Pd, Te, Ba and Nd. The Strutinsky collective potential and cranking inertial functions were obtained using the Nilsson potential. The effect of coupling with the pairing vibrations is taken into account approximately when determining the inertial functions. The calculation does not contain any free parameter
Stability of bubble nuclei through Shell-Effects
We investigate the shell structure of bubble nuclei in simple
phenomenological shell models and study their binding energy as a function of
the radii and of the number of neutron and protons using Strutinsky's method.
Shell effects come about, on the one hand, by the high degeneracy of levels
with large angular momentum and, on the other, by the big energy gaps between
states with a different number of radial nodes. Shell energies down to -40 MeV
are shown to occur for certain magic nuclei. Estimates demonstrate that the
calculated shell effects for certain magic numbers of constituents are probably
large enough to produce stability against fission, alpha-, and beta-decay. No
bubble solutions are found for mass number A < 450.Comment: 9 pages and 9 figures in the eps format include
The low-lying quadrupole collective excitations of Ru and Pd isotopes
Quadrupole excitations of even-even Ru and Pd isotopes are described within
microscopic approach based on the general collective Bohr model which includes
the effect of coupling with the pairing vibrations. The excitation energies and
E2 transition probabilities observed in 104-114Ru and 106-110Pd are reproduced
in the frame of the calculation containing no free parameters.Comment: 11 pages, 18 figures in EPS forma
Fission Fragment Mass and Kinetic Energy Yields of Fermium Isotopes
A rapidly converging 4-dimensional Fourier shape parametrization is used to
model the fission process of heavy nuclei. Potential energy landscapes are
computed within the macroscopic-microscopic approach, on top of which the
multi-dimensional Langevin equation is solved to describe the fission dynamics.
Charge equilibration at scission and de-excitation by neutron evaporation of
the primary fragments after scission is investigated. The model describes
various observables, including fission-fragment mass, charge, and kinetic
energy yields, as well as post-scission neutron multiplicities and, most
importantly, their correlations, which are crucial to unravel the complexity of
the fission process. The parameters of the dynamical model were tuned to
reproduce experimental data obtained from thermal neutron-induced fission of
U, which allows us to discuss the transition from asymmetric to
symmetric fission along the Fm isotopic chain.Comment: Presented at the Mazurian Lakes Conference on Physics, 2023, Polan
The lipid head group is the key element for substrate recognition by the P4 ATPase ALA2:A phosphatidylserine flippase
Type IV P-type ATPases (P4 ATPases) are lipid flippases that catalyze phospholipid transport from the exoplasmic to the cytoplasmic leaflet of cellular membranes, but the mechanism by which they recognize and transport phospholipids through the lipid bilayer remains unknown. In the present study, we succeeded in purifying recombinant aminophospholipid ATPase 2 (ALA2), a member of the P4 ATPase subfamily in Arabidopsis thaliana, in complex with the ALA-interacting subunit 5 (ALIS5). The ATP hydrolytic activity of the ALA2-ALIS5 complex was stimulated in a highly specific manner by phosphatidylserine. Small changes in the stereochemistry or the functional groups of the phosphatidylserine head group affected enzymatic activity, whereas alteration in the length and composition of the acyl chains only had minor effects. Likewise, the enzymatic activity of the ALA2-ALIS5 complex was stimulated by both mono- and di-acyl phosphatidylserines. Taken together, the results identify the lipid head group as the key structural element for substrate recognition by the P4 ATPase
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