| 1. |
|
|
| 2. |
- Dong, G J, et al.
(author)
-
Super-Gaussian mirror for high-field-seeking molecules
- 2005
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:3
-
Journal article (peer-reviewed)abstract
- A matter wave mirror using a single, pulsed, super-Gaussian (SG) optical beam for specular reflection of neutral ground-state molecules is studied. The mirror has a high reflectivity close to 100% and nearly perfect specular reflection over a large incident angle. This mirror avoids the usual problems due to surface roughness and the van der Waals interactions that occur in conventional atomic mirrors. Further, it is capable of reflectance and transmittance with applications to velocity filtering and deceleration of cold molecules.
|
|
| 3. |
- Edvardsson, Sverker, et al.
(author)
-
A Note on Wet Paper Web Adhesion Strength
- 2012
-
In: Journal of Testing and Evaluation. - 0090-3973 .- 1945-7553. ; 40:4, s. 682-686
-
Journal article (peer-reviewed)abstract
- This work is concerned with the determination of the adhesion strength between a paper web and an adhesive surface. Edvardsson et al. [Edvardsson, S., Gradin, P., and Isaksson, P., "On Dissipative Effects of Paper Web Adhesion Strength," Int. J. Solids Struct., Vol. 48(1), 2011, pp. 24-30] suggested recently a model that takes into account the energy dissipation caused by elastic plastic deformation in the bent structure of a paper specimen. This model is further developed and investigated in the present work. A linear relation in plastic dissipation is discovered facilitating a novel analysis of the peeling tension and a more convenient determination of the proper adhesion strength. Industrial relevant examples are made with wet newsprint and kraft stock. A straightforward experimental procedure for determining the consistent adhesion strength is suggested. It is found that the agreement between the model and the experimental observations is good.
|
|
| 4. |
- Edvardsson, Sverker, et al.
(author)
-
A program for accurate solutions of two-electron atoms
- 2004
-
In: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 165:3, s. 260-270
-
Journal article (peer-reviewed)abstract
- We present a comprehensible computer program capable of treating non-relativistic ground and excited states for a twoelectron atom having infinite nuclear mass. An iterative approach based on the implicitly restarted Arnoldi method (IRAM) is employed. The Hamiltonian matrix is never explicitly computed. Instead the action of the Hamiltonian operator on discrete pair functions is implemented. The finite difference method is applied and subsequent extrapolations gives the continuous grid result. The program is written in C and is highly optimized. All computations are made in double precision. Despite this relatively low degree of floating point precision (48 digits are not uncommon), the accuracy in the results can reach about 10 significant figures. Both serial and parallel versions are provided. The parallel program is particularly suitable for shared memory machines such as the Sun Starcat series. The serial version is simple to compile and should run on any platform.
|
|
| 5. |
- Edvardsson, Sverker, et al.
(author)
-
A search for H/ACA snoRNAs in yeast using MFE secondary structure prediction
- 2003
-
In: Bioinformatics. - : Oxford University Press (OUP). - 1367-4803 .- 1367-4811. ; 19:7, s. 865-873
-
Journal article (peer-reviewed)abstract
- We develop an algorithm to screen the yeast genome for novel H/ACA snoRNAs. To achieve this, we introduce some new methods for facilitating the search for noncoding RNAs in genomic sequences which are based on properties of predicted minimum free-energy (MFE) secondary structures. The algorithm has been implemented and can be generalized to enable screening of other eukaryote genomes. We find that use of primary sequence alone is insufficient for identifying novel H/ACA snoRNAs. Only the use of secondary structure filters reduces the number of candidates to a manageable size. From genomic context, we identify three strong H/ACA snoRNA candidates. These together with a further 47 candidates obtained by our analysis are being experimentally screened.
|
|
| 6. |
- Edvardsson, Sverker, et al.
(author)
-
A study of vibrational modes in Na(+)beta-Alumina by molecular-dynamics simulation
- 1994
-
In: JOURNAL OF PHYSICS - CONDENSED MATTER. - 0953-8984 .- 1361-648X. ; 6:7, s. 1319-1332
-
Journal article (peer-reviewed)abstract
- The vibrational properties of crystalline Na+ beta-alumina (Na1.22Al11O17.11) have been studied using the molecular dynamics simulation technique. The vibrational density of states was calculated from the velocity autocorrelation function, and the infrared spectrum from the dipole-dipole autocorrelation function. Knowledge of the vibrations in different crystallographic directions for the different atomic species facilitates the assignment of spectral peaks. The sodium in-plane vibrations are 59, 88 and 112 cm-1, and the out-of-plane vibrations are at 146 cm-1. The stoichiometric compound is also studied, and in this case the sodium in-plane vibrations are at 80 cm-1 and the out-of-plane vibrations at 140 cm-1. The density of states is used to calculate thermodynamic properties: heat capacity, entropy and internal and free energy. The values obtained at 300 K are C(upsilon) = 410 J K-1 mol-1, S(upsilon) = 300 J K-1 mol-1, U = 370 kJ mol-1 and F = 280 kJ mol 1. The heat capacity and entropy values are in good agreement with experiment, and thus strongly support the empirical force field used in the simulation
|
|
| 7. |
- Edvardsson, Sverker, et al.
(author)
-
Accurate spin axes and solar system dynamics: climatic variations for the Earth and Mars
- 2002
-
In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 384:2, s. 689-701
-
Journal article (peer-reviewed)abstract
- Celestial mechanical simulations from a purely classical point of view of the solar system, including our Moon and the Mars moons {Phobos and Deimos {are carried out for 2 millions of years before present. Within the classical approximation, the results are derived at a very high level of accuracy. Effects from general relativity for a number of variables are investigated and found to be small. For climatic studies of about 1 Myr, general relativity can safely be ignored. Three different and independent integration schemes are used in order to exclude numerical anomalies. The converged results from all methods are found to be in complete agreement. For verification, a number of properties such as spin axis precession, nutation, and orbit inclination for Earth and Mars have been calculated. Times and positions of equinoxes and solstices are continously monitored. As also observed earlier, the obliquity of the Earth is stabilized by the Moon. On the other hand, the obliquity of Mars shows dramatic variations. Climatic influences due to celestial variables for the Earth and Mars are studied. Instead of using mean insolation as in the usual applications of Milankovitch theory, the present approach focuses on the instantaneous solar radiation power (insolation) at each summer solstice. Solar radiation power is compared to the derivative of the icevolume and these quantities are found to be in excellent agreement. Orbital precessions for the inner planets are studied as well. In the case of Mercury, it is investigated in detail.
|
|
| 8. |
- Edvardsson, Sverker, et al.
(author)
-
An atomic program for energy levels of equivalent electrons: lanthanides and actinides
- 2001
-
In: Computer Physics Communications. - 0010-4655 .- 1879-2944. ; 133:2/3, s. 396-406
-
Journal article (peer-reviewed)abstract
- A program written in C is presented to carry out brute force calculations in order to derive energy levels for an equivalent electronic configuration. Relativistic effects are partly neglected except for the spin-orbit interaction. Since the main relativistic effects are indirect, i.e. causing a contraction of the core which in turn causes the outer shells to expand, they are included to a high degree through the use of appropriate Slater integrals. The program is especially useful for primarily unfilled f-shells of the rare-earth or actinide ions. Modifications of the program to include spin−spin, spin−other orbit, Breit interaction etc. is straight forward. The program is also general in the sense that there is no need to find out or generate any Racah coefficients of fractional parentage. The complete energy matrix is diagonalized with all operators interacting simultaneously thus allowing mixing of all quantum numbers. This result in all energy eigenvalues and eigenvectors that in turn for example are partly responsible for the polarized dipole, quadrupole, … transitions within the unfilled shell. Free ion configuration interaction is accounted for through the use of standard CI operators. The Stark splitting can be studied via the standard crystal field Hamiltonian. Magnetic field influence on the energy levels may also be studied.
|
|
| 9. |
- Edvardsson, Sverker, et al.
(author)
-
corr3p_tr : A particle approach for the general three-body problem
- 2016
-
In: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 200, s. 259-273
-
Journal article (peer-reviewed)abstract
- This work presents a convenient way to solve the non-relativistic Schrodinger equation numerically for a general three-particle system including full correlation and mass polarization. Both Coulombic and non-Coulombic interactions can be studied. The eigensolver is based on a second order dynamical system treatment (particle method). The Hamiltonian matrix never needs to be realized. The wavefunction evolves towards the steady state solution for which the Schrodinger equation is fulfilled. Subsequent Richardson extrapolations for several meshes are then made symbolically in matlab to obtain the continuum solution. The computer C code is tested under Linux 64 bit and both double and extended precision versions are provided. Test runs are exemplified and, when possible, compared with corresponding values in the literature. The computer code is small and self contained making it unusually simple to compile and run on any system. Both serial and parallel computer runs are straight forward. Program summary Program title: corr3p_tr Catalogue identifier: AEYR_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEYR_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.ukilicence/licence.html No. of lines in distributed program, including test data, etc.: 15025 No. of bytes in distributed program, including test data, etc.: 156430 Distribution format: tar.gz Programming language: ANSI C. Computer: Linux 64bit PC. Operating system: Linux 64bit. RAM: 300 M bytes Classification: 2.7, 2.8, 2.9. Nature of problem: The Schrodinger equation for an arbitrary three -particle system is solved using finite differences and a fast particle method for the eigenvalue problem [20, 21, 23]. Solution method: A fast eigensolver is applied (see Appendix). This solver works for both symmetrical and nonsymmetrical matrices (which opens up for more accurate nonsymmetrical finite difference expressions to be applied at the boundaries). The three-particle Schrodinger equation is transformed in two major steps. First step is to introduce the function Q(r(1), (r)2, mu) = r(1)r(2)(1 - mu(2))phi(r(1), r(2), mu), where mu = cos (0(12)). The cusps (r(1) = r(2), mu = 1) are then transformed into boundary conditions. The derivatives of Qare then continuous in the whole computational space and thus the finite difference expressions are well defined. Three-particle coalescence (r(1) = r(2) = 0, mu) is treated in the same way. The second step is to replace Q(r(1), r(2), mu) with (2,root x(1)x(2))(-1)Q(x(1) x(2), mu). The space (x(1), x(2), mu) is much more appropriate for a finite difference approach since the square roots x(1) = root r(1), x(2) = root r(2) allow the boundaries to be much further out. The non-linearity of the x-grid also leads to a finer description near the nucleus and a coarser one further out thus resulting in a saving of grid points. Also, in contrast to the usual variable r(12), we have instead used mu which is an independent variable. This simplifies the mathematics and numerical treatments. Several different grids can naturally run completely independent of each other thus making parallel computations trivial. From several grid results the physical property of interest is extrapolated to continuum space. The extrapolations are made in a matlab m-script where all computations can be made symbolically so the loss of decimal figures are minimized during this process. The computer code, including correlation effects and mass polarization, is highly optimized and deals with either triangular or quadratic domains in (x(1), x(2)). Restrictions: The amount of CPU time may become unreasonable for states needing boundary conditions very far beyond the origin. Also if the condition number of the corresponding Hamiltonian matrix is very high, the number of iterations will grow. The use of double precision computations also puts a limit on the accuracy of extrapolated results to about 6-7 decimal figures. Unusual features: The numerical solver is based on a particle method presented in [20, 21, 23]. In the Appendix we provide specific details of dealing with eigenvalue problems. The program uses a 64 bit environment (Linux 64bit). Parallel runs can be made conveniently through a simple bash script. Additional comments: The discretized wavefunction is complete on every given grid. New interactions can therefore conveniently be added to the Hamiltonian without the need to seek for an appropriate basis set. Running time: Given a modern CPU such as Intel core i5 and that the outer boundary conditions of r(1) and r(2) is limited to, say 16 atomic units, the total CPU time of totally 10 grids of a serial run is typically limited to a few minutes. One can then expect about 6-7 correct figures in the extrapolated eigenvalue. A single grid of say h(1) = h(2) = h(3) = 1/16 converges in less than 1 s (with an error in the eigenvalue of about 1 percent). Parallel runs are possible and can further minimize CPU times for more demanding tasks. References: [20] S. Edvardsson, M. Gulliksson, and J. Persson.). Appl. Mech. ASME, 79 (2012) 021012. [21] S. Edvardsson, M. Neuman, P Edstrom, and H. Olin. Comp. Phys. Commun. 197 (2015) 169. [23] M. Neuman, S. Edvardsson, P. Edstrom, Opt. Lett. 40 (2015) 4325.
|
|
| 10. |
- Edvardsson, Sverker
(author)
-
Future iceages for the next 100,000 years
- 2002
-
In: The handling of timescales in assessing post-closure safety of deep geological repositories. - Paris : Nuclear Energy Agency, OECD. - 9264099115 ; , s. 212-
-
Conference paper (other academic/artistic)
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
- Edvardsson, Sverker, et al.
(author)
-
On dissipative effects of paper web adhesion strength
- 2011
-
In: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 48:1, s. 24-30
-
Journal article (peer-reviewed)abstract
- This work is concerned with the adhesion strength between a paper web and a metal roll surface, which is a common situation in paper machines world-wide. It is shown that the classic expression relating the work of adhesion to the peeling angle and web tension is, in general, insufficient. An improved model is suggested to take into account the energy dissipation due to elastic-plastic deformation behavior of wet paper materials. To judge the model, an industrially relevant example of wet newsprint and a mild steel surface is studied. It is found that the agreement between theory and experimental observations is excellent. A key result is that elastic-plastic material behavior must always be included for wet paper materials in peeling processes.
|
|
| 14. |
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
- Edvardsson, Sverker, et al.
(author)
-
Sensitivity of optical absorption intensities for rare-earth ions
- 1992
-
In: Physical Review B. - 0163-1829. ; 45:19, s. 10918-10923
-
Journal article (peer-reviewed)abstract
- A technique is presented that uses molecular-dynamics simulation to generate the atomic positions needed to calculate the crystal-field parameters used in a Judd-Ofelt (JO) analysis. A slightly modified theory is used that permits analysis of both pi- and sigma-polarized absorption spectra. Different temperatures and ranges of calculation (up to 8 angstrom) around one rare-earth ion are used in the simulation of our test compound, Nd2O3. It is shown that as many of the surrounding ions as possible should be included in the calculations, and also that it is possible to probe the sensitivity of the different transitions in rare-earth-ion spectra. It is further shown that the behavior of the so-called hypersensitive transition for a rare-earth ion is a result of the sensitivity of the JO parameter OMEGA-2, which is proportional to the square of the electric field created by the surrounding ions.
|
|
| 18. |
- Edvardsson, Sverker, et al.
(author)
-
Solving equations through particle dynamics
- 2015
-
In: Computer Physics Communications. - : Elsevier. - 0010-4655 .- 1879-2944. ; 197, s. 169-181
-
Journal article (peer-reviewed)abstract
- The present work evaluates a recently developed particle method (DFPM). The basic idea behind this method is to utilize a Newtonian system of interacting particles that through dissipation solves mathematical problems. We find that this second order dynamical system results in an algorithm that is among the best methods known. The present work studies large systems of linear equations. Of special interest is the wide eigenvalue spectrum. This case is common as the discretization of the continuous problem becomes dense. The convergence rate of DFPM is shown to be in parity with that of the conjugate gradient method, both analytically and through numerical examples. However, an advantage with DFPM is that it is cheaper per iteration. Another advantage is that it is not restricted to symmetric matrices only, as is the case for the conjugate gradient method. The convergence properties of DFPM are shown to be superior to the closely related approach utilizing only a first order dynamical system, and also to several other iterative methods in numerical linear algebra. The performance properties are understood and optimized by taking advantage of critically damped oscillators in classical mechanics. Just as in the case of the conjugate gradient method, a limitation is that all eigenvalues (spring constants) are required to be of the same sign. DFPM has no other limitation such as matrix structure or a spectral radius as is common among iterative methods. Examples are provided to test the particle algorithm’s merits and also various performance comparisons with existent numerical algorithms are provided.
|
|
| 19. |
- Edvardsson, Sverker, et al.
(author)
-
Spin axis variations of Mars: numerical limitations and model dependences
- 2008
-
In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 135:4, s. 1151-1160
-
Journal article (peer-reviewed)abstract
- Celestial mechanical integrations for the whole solar system are carried out over four billion years before and after the present. The orbital solution of the solar system is stable during this whole time period. An instantaneous spin axis model including triaxiality is developed. In particular, spin axis precession, the Martian obliquity, solar torques, and the orbital eccentricity/inclination of Mars are studied. Model dependences from general relativity, solar oblateness, the Martian moons, solar mass loss, etc. are tested. Although the obliquity of Mars sometimes shows dramatic variations, some structures are robust and seem insensitive to the initial spin precession rate. A full integration is carried out during a total of 8000 Myr resulting in a Martian obliquity that is restricted between 10 and 60 degrees. The problems with numerical noise due to limited machine precision, integration step sizes, and the chaotic sensitivity of the solutions are studied and discussed. The limited machine precision (15-16 figures) alone is found to limit the duration of exact obliquity solutions to about 80 Myr.
|
|
| 20. |
- Edvardsson, Sverker, et al.
(author)
-
System dynamics of the open draw with web adhesion: Particle approach
- 2010
-
In: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 77:2, s. 1-11
-
Journal article (peer-reviewed)abstract
- In the present work we propose a particle approach, which is designedto treat complex mechanics and dynamics of the open-draw sections thatare still present in many of today's paper machines. First, knownsteady-state continuous solutions are successfully reproduced. However,it is shown that since the boundary conditions depend on the solutionitself, the solutions for web strain and web path in the open-drawsection are generally time-dependent. With a certain set of systemparameters, the nonsteady solutions are common. A temporal fluctuationof Young's modulus, for example, destabilizes the system irreversibly,resulting in the continuous growth of web strain, i.e., break. Finallywe exemplify with some strategic draw countermeasures how to prevent adangerous evolution in the web strain.
|
|
| 21. |
- Edvardsson, Sverker, et al.
(author)
-
System stability of the open draw section and paper machine runnability
- 2009
-
In: ADVANCES IN PULP AND PAPER RESEARCH, OXFORD 2009, VOLS 1-3. - 9780954527266 ; , s. 557-575
-
Conference paper (peer-reviewed)abstract
- The present work is concerned with the system dynamics and stability of the open draw sections of paper machines where web breaks occur most frequently. We have applied a novel particle-based system dynamics model that allows the investigation of complex interactions between web property fluctuations and system parameters, without any constraints of a particular geometrical web shape or boundary conditions assumed a priori. The result shows that, at a given machine draw and web property parameters, the open draw section maintains its steady-state until it reaches a certain machine speed limit. At this speed the system looses its stability and the web strain starts growing without any limit, and thus leading to a web break. A similar instability can also be triggered when web properties suddenly fluctuate during steady-state operation. The parametric sensitivity studies indicate that, among the web property parameters studied, the elastic modulus of the wet web has the largest impact on the critical machine speed as well as on the detachment point where the web is released from the first roll. Further analysis shows that the decrease in dryness has a (negative) synergistic effect causing an increased risk of system instability. It is, therefore, most important to control, not only average dryness, but also its variations in order to enhance paper machine runnability.
|
|
| 22. |
- Edvardsson, Sverker, et al.
(author)
-
The connection between the dynamic intensity model and the vibronic intensity model for f-f transitions
- 2006
-
In: Journal of physics. B: Atomic, molecular and optical physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:9, s. 2127-2143
-
Journal article (peer-reviewed)abstract
- In this paper we discuss intensity mechanisms of interest for rare-earth ions in optical materials. More specifically, we investigate the character of two models-first, a semi-classical dynamic intensity model, and second, a more traditional quantum mechanical vibronic intensity model. We focus on the case of f-f transitions and show that the predicted oscillator strengths then are the same under very reasonable approximations. We emphasize that this connection between the models cannot be made in the case of f-d transitions. The dynamic intensity model has an interesting classical interpretation. We show that it is very convenient to apply this approach together with classical dynamical techniques such as molecular dynamics simulation or the classical Monte Carlo method. The classical approach simplifies both the interpretation and calculation of vibronic oscillator strengths in complex systems. The concept of an effective temperature works as a bridge between the two models; so realistic predictions can be obtained even at low temperatures.
|
|
| 23. |
|
|
| 24. |
- Edvardsson, Sverker, 1964-, et al.
(author)
-
The dynamical functional particle method: an approach for boundary value problems
- 2012
-
In: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 79:2, s. art. no. 021012-
-
Journal article (peer-reviewed)abstract
- The present work is concerned with new ideas of potential value for solving differential equations. First, a brief introduction to particle methods in mechanics is made by revisiting the vibrating string. The full case of nonlinear motion is studied and the corresponding nonlinear differential equations are derived. It is suggested that the particle origin of these equations is of more general interest than usually considered. A novel possibility to develop particle methods for solving differential equations in a direct way is investigated. The dynamical functional particle method (DFPM) is developed as a solution method for boundary value problems. DFPM is based on the concept of an interaction functional as a dynamical force field acting on quasi particles. The approach is not limited to linear equations. We exemplify by applying DFPM to several linear Schrödinger type of problems as well as a nonlinear case. It is seen that DFPM performs very well in comparison with some standard numerical libraries. In all cases, the convergence rates are exponential in time. © 2012 American Society of Mechanical Engineers.
|
|
| 25. |
- Edvardsson, Sverker, et al.
(author)
-
The energy matrix using determinantal product states applied to Ho:YAG
- 2000
-
In: Journal of Alloys and Compounds. - 0925-8388 .- 1873-4669. ; 303-304, s. 280-284
-
Journal article (peer-reviewed)abstract
- A program written in C is applied for calculations of energy levels and wavefunctions of the lanthanides or actinides. Standard non-relativistic phenomenological operators are used. Simple determinantal product states are used to form the basis set. The complete energy matrix is diagonalized with all operators interacting simultaneously thus allowing mixing of all quantum numbers. The crystal field splitting can also be studied via the standard crystal field hamiltonian as well as the magnetic field influence on the energy levels. The program is here applied to the technologically interesting trivalent ion holmium which is used to form extremely strong magnets as well as the medical eye-safe laser Ho:YAG. Both experimentally fitted and calculated self-consistent crystal field parameters are used to study the energy structure. Crystal ionic polarizabilities with electron correlation included are partly calculated. Zeeman split levels are also studied.
|
|
| 26. |
- Edvardsson, Sverker, et al.
(author)
-
The use of CI calculated polarizabilities to study rare-earth CFP dependencies in the laser host RE:YLF
- 1999
-
In: Materials Science Forum. - 0255-5476. ; 315/317, s. 407-414
-
Journal article (peer-reviewed)abstract
- It has earlier been shown that the Sternheimer method is appropriate in deriving crystal field parameters (CFP) for Pr3+ and Nd3+ doped in YLF or Nd3+ in YAG. In this connection, the dipole (αD) and quadrupole (αQ) polarizabilities for the whole rare-earth (RE) series will be presented. These are needed for the self consistent lattice summations performed. The various rare-earth wavefunctions needed for the computations are derived from the well known relativistic full Hartree-Fock code by R. D. Cowan. The main CFP behaviour for the various RE dopants in YLF are seen to agree fairly well with the experimentally fitted parameters. Covalency effects are, as expected, observed to be more important for higher order parameters. It is also seen that the contribution to the crystal field due to covalency is approximately constant for a given Btp. This observation is also supported by calculations of Newman. The shielding, nuclear antishielding factors and radial integrals for the whole RE series are also presented.
|
|
| 27. |
- Edvardsson, Sverker, et al.
(author)
-
Use of polarized optical absorption to obtain structural information for Na1/Nd31 b9-alumina
- 1996
-
In: Physical Review B, Condensed matter. - 0163-1829. ; 54:24, s. 17476-17 485
-
Journal article (peer-reviewed)abstract
- Part of the optical absorption spectrum is calculated for the Nd31-doped Na1 b9-alumina using a moleculardynamics-~MD! based approach. The Judd/Ofelt ~J/O! theory is modified ~and several approximations removed! to treat polarized transition intensities for rare-earth ions in a solid host. Stark-level energies and eigenfunctions of the ground state ~4I9/2! and excited multiplets (4F3/2,2P1/2) are also calculated for the local environments involved. Energies and polarized transition intensities between individual Stark levels are thus calculated simultaneously for several hundreds of MD-generated environments; summation gives the total bandshape. A high proportion of Beevers-Ross-site occupation ~.50%! is indicated for low Nd31 concentrations in b9-alumina. The contrary is observed experimentally for high Nd31 concentrations, i.e., then midoxygen site occupation dominates. It is demonstrated that ions in different local environments contribute differently to the absorption spectrum and, particularly, how the polarization of the various transitions changes for ions occupying different sites. Temperature dependence aspects are also considered
|
|
| 28. |
- Engholm, Magnus, et al.
(author)
-
A structural investigation of a synthesized precursor for fiber optical applications; the heterobimetallic ErNb_2(OPr^i)_13
- 2006
-
In: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 29:4, s. 386-391
-
Journal article (peer-reviewed)abstract
- A structural investigation of a synthesized precursor in a silica glass matrix is performed. Silica soot samples are doped with the heterobimetallic precursor ErNb2(OPri)13 by using a conventional solution doping technique and heat treatments to different temperatures. The precursor has also been introduced into a silica fiber preform by using the modified chemical vapor deposition technique. Analyses are made by using ultraviolet–visible–near infrared absorption spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and powder X-ray diffraction. It is concluded that an immiscible system of ErNbO4 crystallites and Nb2O5 is formed in the silica soot samples at high temperatures. Colloidal particles of ErNbO4 are also formed in the silica glass fiber preform showing interesting features.
|
|
| 29. |
|
|
| 30. |
- Flipse, C. F. J, et al.
(author)
-
XPS study of the new superconductor Nd-Ce-Cu-O
- 1989
-
In: Physica C: Superconductivity. - : Elsevier BV. - 0921-4534. ; 162-164:2, s. 1389-1390
-
Journal article (peer-reviewed)abstract
- In this paper we present XPS and Auger measurements on Nd1.85Ce0.15CuO3.96 and its parent material. These measurements show that electron doping, by substitution of Ce4+ in the case of Nd3+, results in a filling of the Cu 3d9 states. So the Ce doped compound will have a higher 3d10 contribution. The intensity of the Cu-2p satellite is very low for this new superconductor with respect to the high-Tc superconductors.
|
|
| 31. |
- Freyhult, Eva, et al.
(author)
-
Fisher: a program for the detection of H/ACA snoRNAs using MFE secondary structure prediction and comparative genomics - assessment and update
- 2008
-
In: BMC Research Notes. - : Springer Science and Business Media LLC. - 1756-0500. ; 1:49, s. 1-8
-
Journal article (peer-reviewed)abstract
- BackgroundThe H/ACA family of small nucleolar RNAs (snoRNAs) plays a central role in guiding the pseudouridylation of ribosomal RNA (rRNA). In an effort to systematically identify the complete set of rRNA-modifying H/ACA snoRNAs from the genome sequence of the budding yeast, Saccharomyces cerevisiae, we developed a program - Fisher - and previously presented several candidate snoRNAs based on our analysis [1]. FindingsIn this report, we provide a brief update of this work, which was aborted after the publication of experimentally-identified snoRNAs [2] identical to candidates we had identified bioinformatically using Fisher. Our motivation for revisiting this work is to report on the status of the candidate snoRNAs described in [1], and secondly, to report that a modified version of Fisher together with the available multiple yeast genome sequences was able to correctly identify several H/ACA snoRNAs for modification sites not identified by the snoGPS program [3]. While we are no longer developing Fisher, we briefly consider the merits of the Fisher algorithm relative to snoGPS, which may be of use for workers considering pursuing a similar search strategy for the identification of small RNAs. The modified source code for Fisher is made available as supplementary material. ConclusionOur results confirm the validity of using minimum free energy (MFE) secondary structure prediction to guide comparative genomic screening for RNA families with few sequence constraints.
|
|
| 32. |
|
|
| 33. |
- Hellström, Lisbeth M., et al.
(author)
-
A theoretical and experimental study of the circular sawing process
- 2014
-
In: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:3, s. 307-312
-
Journal article (peer-reviewed)abstract
- To gain further insight into the energy dissipation during the wood sawing process, a theoretical model has been developed. The model is based on the assumption that there are two basic causes for energy dissipation during sawing: the creation of a new surface and the compression of material below a saw tooth. It is assumed that both contributions can be dependent on the cutting angle (the angle between the fiber direction and the tangent to the path followed by a saw tooth) because a saw tooth changes its angle of attack during its way through a log. To determine this dependence of the dissipation on the cutting angle, a series of experiments with pine plank sawing were performed by means of different feeding rates and cutting angles while the electrical power supplied to the saw was measured. The parameters in the theoretical model were derived from the experimental findings. Finally, two tests were carried out under different conditions with respect to thickness and cutting angles and the validity of the model was confirmed concerning the prediction of the electrical power consumption.
|
|
| 34. |
- Klintenberg, Mattias, et al.
(author)
-
Calculation of energy levels and polarized oscillator strengths for Nd3+:YAG
- 1997
-
In: Physical review. B, Condensed matter. - 0163-1829. ; 55:16, s. 10369-10375
-
Journal article (peer-reviewed)abstract
- The effect of an electrostatic crystal-field (CF) model on energy levels and oscillator strengths for Nd3+:YAG (where YAG denotes yttrium aluminum garnet) has been studied. Three parameters for the correction of the Slater integrals F2, F4, and F6 and one parameter to correct the spin-orbit constant for the effects of the linear configuration interaction have been introduced. The complete 364×364 energy matrix has been diagonalized directly. The various polarizabilities and shielding parameters used have been calculated by ab initio methods. All Stark levels within the Nd3+(4f3) configuration are presented. The calculated Stark splittings agree well with experiment. The electrostatic CF model used is therefore believed to be satisfactory. The eigenvectors of the complete energy matrix have been used to calculate oscillator strengths, which agree well with experiment. A refined Judd-Ofelt theory has been used. The Judd-Ofelt intensity parameters Ωλ are presented and found to be in excellent agreement with experiment. The temperature dependence of the spectrum is studied using a molecular-dynamics approach.
|
|
| 35. |
|
|
| 36. |
|
|
| 37. |
- Klintenberg, Mattias, et al.
(author)
-
The use of molecular dynamics to simulate the temperature dependence of the calculated absorption spectrum for Nd3+:YAG
- 1999
-
In: Materials Science Forum. - 0255-5476. ; 315-317, s. 42-50
-
Journal article (peer-reviewed)abstract
- The use of molecular dynamics (MD) and the inclusion of configuration interaction (CI) effects have been shown to be important in the simulation of polarized absorption spectra for rare-earth doped compounds. This work, focuses on how well the MD approach can account for the temperature dependence of the calculated absorption spectrum for Nd3+:YAG, using the standard MD pair-potential of the Born-Mayer-Huggins form. All simulated spectra are compared to the corresponding experimental spectra. The results indicate that the simple pair-potential must be replaced by a many-body potential to describe the motion of the ions with sufficient accuracy. They also suggest that an “effective temperature” (T') should be used in the MD simulation of the form T'=aT+b
|
|
| 38. |
|
|
| 39. |
|
|
| 40. |
|
|
| 41. |
- Neuman, Magnus, et al.
(author)
-
Solving the radiative transfer equation with a mathematical particle method
- 2015
-
In: Optics Letters. - : Optics Info Base, Optical Society of America. - 0146-9592 .- 1539-4794. ; 40:18, s. 4325-4328
-
Journal article (peer-reviewed)abstract
- We solve the radiative transfer equation (RTE) using a recently proposed mathematical particle method, originally developed for solving general functional equations. We show that, in the case of the RTE, it gives several advantages, such as handling arbitrary boundary conditions and phase functions and avoiding numerical instability in strongly forward-scattering media. We also solve the RTE, including fluorescence, and an example is shown with a fluorescence cascade where light is absorbed and emitted in several steps. We show that the evaluated particle method is straightforward to implement, which is in contrast with many traditional RTE solvers, but a potential drawback is the tuning of the method parameters.
|
|
| 42. |
- Ning, Lixin, et al.
(author)
-
Dynamic intensity model calculation of vibronic oscillator strengths for Cs2NaNdCl6 : A molecular dynamics study
- 2006
-
In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:43, s. 21424-21429
-
Journal article (peer-reviewed)abstract
- We present here a dynamic intensity model calculation of vibronic oscillator strengths for the Cs2NaNdCl6 compound by applying the method of molecular-dynamics simulation (MDS). The force field parameters used for the MDS reproduce the structure and several vibrational frequencies of Cs2NaNdCl6 very well. Both the static-coupling (SC) and dynamic-coupling (DC) mechanisms are taken into account for the intensity parameter calculations, in which the effective point charges and isotropic polarizabilities are optimized with respect to experimental energy levels. A comparison of intensity parameters and vibronic oscillator strengths between the two individual mechanisms indicates that the DC mechanism is operative. The calculated vibronic oscillator strengths for the combined SC and DC mechanism agree quite well with the available experimental values.
|
|
| 43. |
- Ning, Lixin, et al.
(author)
-
Theoretical study ofI-4(13/2) -> I-4(15/2) luminescence quenching by OH for LaF3 : Er3+ nanoparticles in solution
- 2007
-
In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:1
-
Journal article (peer-reviewed)abstract
- The processes of I-4(13/2)-> I-4(15/2) luminescence quenching by OH vibrations are investigated for LaF3:Er3+ nanoparticles dissolved in solution. The energy transfer (ET) rates, involving the I-4(13/2)-> I-4(15/2) transition of Er3+ and the first overtone absorption of OH, are estimated. In order to calculate the relevant OH transition matrix elements, a model for the OH vibration in solution is developed with the use of a Morse potential. Various multipole-multipole ET mechanisms are considered and their dependences on the distance between Er3+ and OH are studied. Based on these ET mechanisms, the ET rates from an Er3+ in the nanoparticle to all the OH in solution are estimated and compared with respect to changes in location of the ion, size of the nanoparticle and OH concentration in solution. The effective I-4(13/2)-> I-4(15/2) luminescence decay times that are contributed by all the Er3+ in the nanoparticle are then calculated with different Er3+ concentrations. The calculations satisfactorily account for experimental observations.
|
|
| 44. |
- Persson, Johan
(author)
-
On dynamic crack growth in discontinuous materials
- 2015
-
Doctoral thesis (other academic/artistic)abstract
- In this thesis work numerical procedures are developed for modeling dynamic fracture of discontinuous materials, primarily materials composed of a load-bearing network. The models are based on the Newtonian equations of motion, and does not require neither stiffness matrices nor remeshing as cracks form and grow. They are applied to a variety of cases and some general conclusions are drawn. The work also includes an experimental study of dynamic crack growth in solid foam. The aims are to deepen the understanding of dynamic fracture by answering some relevant questions, e.g. What are the major sources of dissipation of potential energy in dynamic fracture? What are the major differences between the dynamic fracture in discontinuous network materials as compared to continuous materials? Is there any situation when it would be possible to utilize a homogenization scheme to model network materials as continuous? The numerical models are compared with experimental results to validate their ability to capture the relevant behavior, with good results. The only two plausible dissipation mechanisms are energy spent creating new surfaces, and stress waves, where the first dominates the behavior of slow cracks and the later dominates fast cracks. In the numerical experiments highly connected random fiber networks, i.e. structures with short distance between connections, behaves phenomenologically like a continuous material whilst with fewer connections the behavior deviates from it. This leads to the conclusion that random fiber networks with a high connectivity may be treated as a continuum, with appropriately scaled material parameters. Another type of network structures is the ordered networks, such as honeycombs and semi-ordered such as foams which can be viewed as e.g. perturbed honeycomb grids. The numerical results indicate that the fracture behavior is different for regular honeycombs versus perturbed honeycombs, and the behavior of the perturbed honeycomb corresponds well with experimental results of PVC foam.
|
|
| 45. |
|
|
| 46. |
- Wessely, Ola, et al.
(author)
-
Initial and final state effects in the x-ray absorption process of La1-xSrxMnO3
- 2003
-
In: Physical Review B : Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:23, s. 235109-1
-
Journal article (peer-reviewed)abstract
- We have probed the electronic structure of La1-xSrxMnO3 using x-ray absorption spectroscopy, and compared our results to theory. It is shown that the O projected spectrum reveals a signal that is consistent only with hybridized and delocalized Mn d-states whereas the Mn projected spectrum reveals a signal that can only be reproduced by atomic like theory allowing for multiplet formation between the core hole and the valence electrons of the final state. Our results indicate that the ground state electronic structure has delocalized Mn d-states. This is discussed to be caused by a dynamical screening of the core hole created in the absorption process.
|
|
| 47. |
- Wessley, O, et al.
(author)
-
Final state effects in the X-ray absorption spectra of La0.7Sr0.3MnO3
- 2004
-
In: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 272-276:3, s. 1780-1781
-
Journal article (peer-reviewed)abstract
- We present a comparison of theoretical calculations of the electronic structure of La0.7Sr0.3MnO3 with measurements of the unoccupied local density of states for Mn obtained from X-ray absorption spectroscopy (XAS). We compare two different theoretical calculations of the Mn XAS spectra, one based on the local spin density approximation (LSDA) and the other one based on an atomic Hartree–Fock calculation for the Mn ions. In the atomic calculation the solid state effects are introduced through a cubic crystal field where the crystal field strength is obtained from the LSDA calculation. It is found that the atomic calculations agree better with experimental data.
|
|
| 48. |
- Wolf, Mats, et al.
(author)
-
Molecular dynamics based analysis of the absorption of spectra of Nd3+-doped Na+ β’’-alumina.
- 1993
-
In: Physical Review B. ; 48:14, s. 10129-10136
-
Journal article (peer-reviewed)abstract
- The polarized absorption spectra of Nd3+-doped Na+ beta''-alumina have been treated theoretically for five neodymium concentrations. The perturbing crystal field, needed in the Judd-Ofelt analysis, is calculated from a molecular-dynamics simulation for each composition. Oscillator strengths and Judd-Ofelt intensity parameters are calculated using a point-charge model at each time step in the simulation for each of the Nd3+ ions in the simulation box. A study of the effect of the dynamics of the system on these parameters was also made. The theoretical results thus obtained are compared to experiment. It is shown that the absorption spectra can be explained essentially on the basis of the special structural situation of the Nd3+ ions in these materials.
|
|
| 49. |
- Zhang, Renyun, et al.
(author)
-
High-speed deposition of multilayer nanofilms using soap-film coating
- 2013
-
Conference paper (peer-reviewed)abstract
- High-speed deposition of multilayer nanofilms using soap-film coatingRenyun Zhang, Henrik A. Andersson, Mattias Andersson, Britta Andres, Per Edström, Sverker Edvardsson, Sven Forsberg, Magnus Hummelgård, Niklas Johansson, Kristoffer Karlsson, Hans-Erik Nilsson, Martin Olsen, Tetsu Uesaka, Thomas Öhlund & Håkan OlinDepartment of Applied Science and Design, Mid Sweden University, SE-85170 Sundsvall, SwedenEmail: renyun.zhang@miun.se or hakan.olin@miun.seCoating1 of thin films is of importance for making functionalized surfaces with applications in many fields from electronics to consumer packaging. To decrease the cost, large scale roll-to-roll2 coating techniques are usually done at high speed, for example, ordinary printing paper is coated at a speed of tens of meters per second by depositing micrometer thick layers of clay. However, nanometer thin films are harder to coat at high speed by wet-chemical methods, requiring special roll-to-roll vacuum techniques3 with the cost of higher complexity.Here, we report a simple wet chemical method for high-speed coating of films down to molecular thicknesses, called soap-film coating (SFC)4. The technique is based on forcing a substrate through a soap film that contains nanomaterials. In the simplest laboratory version, the films can be deposited by a hand-coating procedure set up in a couple of minutes. The method is quite general molecules or nanomaterials or sub-micrometer materials (Figure 1) with thicknesses ranging from less than a monolayer to several layers at speeds up to meters per second. The applications of soap-film coating is quite wide an we will show solar cells, electrochromic devices, optical nanoparticle crystals, and nano-film devices. We believe that the soap-film coating method is potentially important for industrial-scale nanotechnology.Fig. 1. Soap film coating of nanoparticles, layered materials, nanowires, and molecules. a sub-monolayer 240 nm silica nanoparticle (scale bar 2 µm) b monolayer c double layer. d monolayer gold nanoparticles. e single layer TiO2 nanoparticles. f sub-monolayer polystyrene (scale 2 µm), g monolayer of polystyrene. h triple-layer of polystyrene. i monolayer of Ferritin. j AFM image of <1.5 layer GO film (3 µm x 2 µm). k clay on glass (scale 2 µm). l SFC coated nanocellulose. m Absorbance spectra Rhodamine B on a glass slide. AFM of SDS layers n (2 µm x 1.5 µm) and o (20 µm x 15 µm).ReferencesTracton, A. A. Coating Technology Handbook (CRC Press, Boca Raton, 2006).Ohring, M. Materials science of thin films. (Academic press., 2001).Charles, B. Vacuum deposition onto webs, films and foils. (William Andrew, 2011).Zhang, R. Y., Andersson, H. A., Andersson, M., Andres, B., Edström, P., Edvardsson, S., Forsberg, S., Hummelgård, M., Johansson, N., Karlsson, K., Nilsson, H.-E., Olsen, M., Uesaka, T., Öhlund, T., Olin H. Soap film coating: High-speed deposition of multilayer nanofilms. Submitted.
|
|
| 50. |
- Zhang, Renyun, et al.
(author)
-
Piezoelectric gated ZnO nanowire diode studied by in situ TEM probing
- 2014
-
In: Nano Energy. - : Elsevier. - 2211-2855. ; 3, s. 10-15
-
Journal article (peer-reviewed)abstract
- The piezoelectricity of ZnO nanowires has shown rising interests during the last few years and fields such as piezotronics and piezophotonics are emerging with a number of applications and devices. One such device is the piezoelectric gated ZnO nanowire diode, where the p–n junction is replaced by a dynamically created potential barrier created simply by bending the otherwise homogeneously doped nanowire. To further study this type of diode we used in situ transmission electron microscope (TEM) probing, where one electrode was fixed at the end of a ZnO nanowire and another moveable electrode was used both for bending and contacting the wire. Thereby we were able to further characterise this diode and found that the diode characteristics depended on whether the contact was made to the stretched (p-type) surface or to the compressed (n-type) surface of the wire. When the neutral line of the wire contacted, between the stretched and the compressed side, the I–V characteristics were independent on the current direction. The performance of the diodes upon different bending intensity showed a rectifying ratio up to the high value of 60:1. The diode ideality factor was found to be about 5. Moreover, the reverse breakdown voltages of the diode were measured and a local but permanent damage to the diode action was found when the voltage went over the reverse breakdown voltage.
|
|
