1,018 research outputs found
Helium 2 3S - 2 1S metrology at 1557 nm
An experiment is proposed to excite the 'forbidden' 1s2s 3S1 - 1s2s 1S0
magnetic dipole (M1) transition at 1557 nm in a collimated and slow atomic beam
of metastable helium atoms. It is demonstrated that an excitation rate of 5000
/s can be realised with the beam of a 2W narrowband telecom fiber laser
intersecting the atomic beam perpendicularly. A Doppler-limited sub-MHz
spectroscopic linewidth is anticipated. Doppler-free excitation of 2% of
trapped and cooled atoms may be realised in a one-dimensional optical lattice
geometry, using the 2W laser both for trapping and spectroscopy. The very small
(8 Hz) natural linewidth of this transition presents an opportunity for
accurate tests of atomic structure calculations of the helium atom. A
measurement of the 3He - 4He isotope shift allows for accurate determination of
the difference in nuclear charge radius of both isotopes.Comment: accepted for publication in Europhysics Letter
Resolving all-order method convergence problems for atomic physics applications
The development of the relativistic all-order method where all single,
double, and partial triple excitations of the Dirac-Hartree-Fock wave function
are included to all orders of perturbation theory led to many important results
for study of fundamental symmetries, development of atomic clocks, ultracold
atom physics, and others, as well as provided recommended values of many atomic
properties critically evaluated for their accuracy for large number of
monovalent systems. This approach requires iterative solutions of the
linearized coupled-cluster equations leading to convergence issues in some
cases where correlation corrections are particularly large or lead to an
oscillating pattern. Moreover, these issues also lead to similar problems in
the CI+all-order method for many-particle systems. In this work, we have
resolved most of the known convergence problems by applying two different
convergence stabilizer methods, reduced linear equation (RLE) and direct
inversion of iterative subspace (DIIS). Examples are presented for B, Al,
Zn, and Yb. Solving these convergence problems greatly expands the
number of atomic species that can be treated with the all-order methods and is
anticipated to facilitate many interesting future applications
THE "GABINETTO OF GILDED STUCCO" IN THE ROYAL PALACE OF PORTICI, NAPLES (ITALY): SURVEY AND DIAGNOSIS FOR CONSERVATION
Abstract. During the 18th century architecture in Naples reached an extremely balanced synthesis between architectural spatiality and decorative apparatuses representing the most successful example of local inventiveness over history. Quite an impressive case dating back to that period is represented by the "Gabinetto of gilded stucco" in the Royal Palace in Portici. Located in the area of the palace known as Caramanico – from the name of the owner of the pre-existing building incorporated in the palace – the stucco was molded between 1752 and 1753 by the two stucco workers Angelo la Sala and Gennaro Bruscino, who also decorated the "Salotto di Porcellana" in Chinese style. Today the room, used as an academic department, is affected by quite a serious stucco decay majorly due to negligence and humidity and consisting in efflorescence, powdering and bursting, worsened by the corrosion of metal fixings. However, the present-day state of conservation of these stuccoworks represents a unique opportunity to carefully observe the original technique used to make such artworks at that time. Therefore by means of advanced surveying instruments and multi-analytical material characterization together with archival documents, the present research – set up in collaboration between University of Naples, Politecnico di Milano and CNR – aims at elaborating a thorough knowledge of an emblematic case of 18th century Neapolitan stucco with a view to its future conservation
Classification of multi-layered plaster in St. Abbondio Cloister at Como, Italy: an analytical tool for architectural archaeology
Clasificación de los revoques multiestratificados del claustro de S. Abbondio en Como (Italia): un instrumento analÃtico para la arqueologÃa de la arquitectura
S. Abbondio (Como, Italia) es una de las mas extraordinariasbasilicas romanicas presentes en el norte de Italia.El edificio entero y en particular el claustro ha sido expuestoa varias intervenciones durante los ultimos siglos, enparticular los ultimos trabajos de conservacion ejecutadosentre los anos 2000 y 2003. En esta ocasion se ha efectuadouna vasta campana diagnostica sobre los revoquestanto internos como externos, destinada a clasificarlosdesde el punto de vista compositivo-morfologico y paradescubrir la historia sobre la conservacion del claustro.Revoques representativos de las diferentes fases constructivashan sido identificados con la utilizacion de metodoscomo el analisis de difraccion de rayos X en polvo,porosimetria por intrusion de mercurio, microscopia opticapara secciones finas y espectrometria atomica. Losresultados han permitido agrupar las muestras que presentabancaracteristicas similares, confirmando hipotesishistoricas sobre la secuencia de las intervenciones en eledificio, sugiriendo un metodo analitico que podria serusado como un instrumento valido en caso de estudiossobre la arqueologia de la arquitectura
Controlled spontaneous emission
The problem of spontaneous emission is studied by a direct computer
simulation of the dynamics of a combined system: atom + radiation field. The
parameters of the discrete finite model, including up to 20k field oscillators,
have been optimized by a comparison with the exact solution for the case when
the oscillators have equidistant frequencies and equal coupling constants.
Simulation of the effect of multi-pulse sequence of phase kicks and emission by
a pair of atoms shows that both the frequency and the linewidth of the emitted
spectrum could be controlled.Comment: 25 pages including 11 figure
Detection of positron-atom bound states through resonant annihilation
A method is proposed for detecting positron-atom bound states by observing
enhanced positron annihilation due to electronic Feshbach resonances at
electron-volt energies. The method is applicable to a range of open-shell
transition metal atoms which are likely to bind the positron: Fe, Co, Ni, Tc,
Ru, Rh, Sn, Sb, Ta, W, Os, Ir, and Pt. Estimates of their binding energies are
provided.Comment: 5 pages, 1 figure; estimates of binding energies have been adde
Spin gaps and spin-flip energies in density-functional theory
Energy gaps are crucial aspects of the electronic structure of finite and
extended systems. Whereas much is known about how to define and calculate
charge gaps in density-functional theory (DFT), and about the relation between
these gaps and derivative discontinuities of the exchange-correlation
functional, much less is know about spin gaps. In this paper we give
density-functional definitions of spin-conserving gaps, spin-flip gaps and the
spin stiffness in terms of many-body energies and in terms of single-particle
(Kohn-Sham) energies. Our definitions are as analogous as possible to those
commonly made in the charge case, but important differences between spin and
charge gaps emerge already on the single-particle level because unlike the
fundamental charge gap spin gaps involve excited-state energies. Kohn-Sham and
many-body spin gaps are predicted to differ, and the difference is related to
derivative discontinuities that are similar to, but distinct from, those
usually considered in the case of charge gaps. Both ensemble DFT and
time-dependent DFT (TDDFT) can be used to calculate these spin discontinuities
from a suitable functional. We illustrate our findings by evaluating our
definitions for the Lithium atom, for which we calculate spin gaps and spin
discontinuities by making use of near-exact Kohn-Sham eigenvalues and,
independently, from the single-pole approximation to TDDFT. The many-body
corrections to the Kohn-Sham spin gaps are found to be negative, i.e., single
particle calculations tend to overestimate spin gaps while they underestimate
charge gaps.Comment: 11 pages, 1 figure, 3 table
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