2,759 research outputs found
Multiconfiguration Dirac-Hartree-Fock energy levels and transition probabilities for 3d^5 in Fe IV
Multiconfiguration Dirac-Hartree-Fock electric quadrupole (E2) and magnetic
dipole (M1) transition probabilities are reported for transitions between
levels of 3d^5 in [Fe IV]. The accuracy of the ab initio energy levels and the
agreement in the length and velocity forms of the line strength for the E2
transitions are used as indicators of accuracy. The present E2 and M1
transition probabilities are compared with earlier Breit-Pauli results and
other theories. An extensive set of transition probabilites with indicators of
accuracy are reported in Appendices A and B. Recommended values of A(E2) +
A(M1) are listed in Appendix C.Comment: 16 pages, three appendices containing accuracy indicators and
recommended values for E2 and M1 transition rate
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A fixed-target platform for serial femtosecond crystallography in a hydrated environment.
For serial femtosecond crystallography at X-ray free-electron lasers, which entails collection of single-pulse diffraction patterns from a constantly refreshed supply of microcrystalline sample, delivery of the sample into the X-ray beam path while maintaining low background remains a technical challenge for some experiments, especially where this methodology is applied to relatively low-ordered samples or those difficult to purify and crystallize in large quantities. This work demonstrates a scheme to encapsulate biological samples using polymer thin films and graphene to maintain sample hydration in vacuum conditions. The encapsulated sample is delivered into the X-ray beam on fixed targets for rapid scanning using the Roadrunner fixed-target system towards a long-term goal of low-background measurements on weakly diffracting samples. As a proof of principle, we used microcrystals of the 24 kDa rapid encystment protein (REP24) to provide a benchmark for polymer/graphene sandwich performance. The REP24 microcrystal unit cell obtained from our sandwiched in-vacuum sample was consistent with previously established unit-cell parameters and with those measured by us without encapsulation in humidified helium, indicating that the platform is robust against evaporative losses. While significant scattering from water was observed because of the sample-deposition method, the polymer/graphene sandwich itself was shown to contribute minimally to background scattering
Calculation of the two-photon decay rates of hydrogen-like ions by using B-polynomials
A new approach is laid out to investigate the two photon atomic transitions.
It is based on application of the finite basis solutions constructed from the
Bernstein Polynomial (B-Polynomial) sets. We show that such an approach
provides a very promising route for the relativistic second- (and even
higher-order) calculations since it allows for analytical evaluation of the
involved matrices elements. In order to illustrate possible applications of the
method and to verify its accuracy, detailed calculations are performed for the
2s_{1/2}-1s_{1/2} transition in neutral hydrogen and hydrogen-like ions, and
are compared with the theoretical predictions based on the well-established
B-spline-basis-set approach
Short wavelength spectrum and Hamiltonian stability of vortex rings
We compare dynamical and energetical stability criteria for vortex rings. It
is argued that vortex rings will be intrinsically unstable against
perturbations with short wavelengths below a critical wavelength, because the
canonical vortex Hamiltonian is unbounded from below for these modes. To
explicitly demonstrate this behaviour, we derive the oscillation spectrum of
vortex rings in incompressible, inviscid fluids, within a geometrical cutoff
procedure for the core. The spectrum develops an anomalous branch of negative
group velocity, and approaches the zero of energy for wavelengths which are
about six times the core diameter. We show the consequences of this dispersion
relation for the thermodynamics of vortex rings in superfluid He at low
temperatures.Comment: 7 pages, 4 figures, final version to appear in Phys. Rev.
Chaos and localization in the wavefunctions of complex atoms NdI, PmI and SmI
Wavefunctions of complex lanthanide atoms NdI, PmI and SmI, obtained via
multi-configuration Dirac-Fock method, are analyzed for density of states in
terms of partial densities, strength functions (), number of principal
components () and occupancies (\lan n_\alpha \ran^E) of single
particle orbits using embedded Gaussian orthogonal ensemble of one plus
two-body random matrix ensembles [EGOE(1+2)]. It is seen that density of states
are in general multi-modal, 's exhibit variations as function of the
basis states energy and 's show structures arising from localized
states. The sources of these departures from EGOE(1+2) are investigated by
examining the partial densities, correlations between , and
\lan n_\alpha \ran^E and also by studying the structure of the Hamiltonian
matrices. These studies point out the operation of EGOE(1+2) but at the same
time suggest that weak admixing between well separated configurations should be
incorporated into EGOE(1+2) for more quantitative description of chaos and
localization in NdI, PmI and SmI.Comment: There are 9 figure
IFMIF suitability for evaluation of fusion functional materials
The International FusionMaterials Irradiation Facility (IFMIF) is a future neutron source based on the D-Li stripping reaction, planned to test candidate fusionmaterials at relevant fusion irradiation conditions. During the design of IFMIF special attention was paid to the structural materials for the blanket and first wall, because they will be exposed to the most severe irradiation conditions in a fusion reactor. Also the irradiation of candidate materials for solid breeder blankets is planned in the IFMIF reference design.
This paper focuses on the assessment of the suitability of IFMIF irradiation conditions for testing functionalmaterials to be used in liquid blankets and diagnostics systems, since they are been also considered within IFMIF objectives. The study has been based on the analysis and comparison of the main expected irradiation parameters in IFMIF and DEMO reactor
Spin-other-orbit operator in the tensorial form of second quantization
The tensorial form of the spin-other-orbit interaction operator in the
formalism of second quantization is presented. Such an expression is needed to
calculate both diagonal and off-diagonal matrix elements according to an
approach, based on a combination of second quantization in the coupled
tensorial form, angular momentum theory in three spaces (orbital, spin and
quasispin), and a generalized graphical technique. One of the basic features of
this approach is the use of tables of standard quantities, without which the
process of obtaining matrix elements of spin-other-orbit interaction operator
between any electron configurations is much more complicated. Some special
cases are shown for which the tensorial structure of the spin-other-orbit
interaction operator reduces to an unusually simple form
An efficient approach for spin-angular integrations in atomic structure calculations
A general method is described for finding algebraic expressions for matrix
elements of any one- and two-particle operator for an arbitrary number of
subshells in an atomic configuration, requiring neither coefficients of
fractional parentage nor unit tensors. It is based on the combination of second
quantization in the coupled tensorial form, angular momentum theory in three
spaces (orbital, spin and quasispin), and a generalized graphical technique.
The latter allows us to calculate graphically the irreducible tensorial
products of the second quantization operators and their commutators, and to
formulate additional rules for operations with diagrams. The additional rules
allow us to find graphically the normal form of the complicated tensorial
products of the operators. All matrix elements (diagonal and non-diagonal with
respect to configurations) differ only by the values of the projections of the
quasispin momenta of separate shells and are expressed in terms of completely
reduced matrix elements (in all three spaces) of the second quantization
operators. As a result, it allows us to use standard quantities uniformly for
both diagona and off-diagonal matrix elements
Relativistic transition wavelenghts and probabilities for spectral lines of Ne II
Transition wavelengths and probabilities for several 2p4 3p - 2p4 3s and 2p4
3d - 2p4 3p lines in fuorine-like neon ion (NeII) have been calculated within
the multiconfiguration Dirac-Fock (MCDF) method with quantum electrodynamics
(QED) corrections. The results are compared with all existing experimental and
theoretical data
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