| 1. |
- Dong, G J, et al.
(författare)
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Super-Gaussian mirror for high-field-seeking molecules
- 2005
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:3
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
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| 3. |
- Edvardsson, Sverker, et al.
(författare)
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Spin axis variations of Mars: numerical limitations and model dependences
- 2008
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 135:4, s. 1151-1160
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Edvardsson, Sverker, et al.
(författare)
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System stability of the open draw section and paper machine runnability
- 2009
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Ingår i: ADVANCES IN PULP AND PAPER RESEARCH, OXFORD 2009, VOLS 1-3. - 9780954527266 ; , s. 557-575
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Konferensbidrag (refereegranskat)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.
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| 5. |
- Edvardsson, Sverker, et al.
(författare)
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The connection between the dynamic intensity model and the vibronic intensity model for f-f transitions
- 2006
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Ingår i: Journal of physics. B: Atomic, molecular and optical physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:9, s. 2127-2143
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Tidskriftsartikel (refereegranskat)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.
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| 6. |
- Engholm, Magnus, et al.
(författare)
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A structural investigation of a synthesized precursor for fiber optical applications; the heterobimetallic ErNb_2(OPr^i)_13
- 2006
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 29:4, s. 386-391
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Tidskriftsartikel (refereegranskat)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.
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| 7. |
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| 8. |
- Freyhult, Eva, et al.
(författare)
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Fisher: a program for the detection of H/ACA snoRNAs using MFE secondary structure prediction and comparative genomics - assessment and update
- 2008
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Ingår i: BMC Research Notes. - : Springer Science and Business Media LLC. - 1756-0500. ; 1:49, s. 1-8
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Tidskriftsartikel (refereegranskat)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.
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| 9. |
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| 10. |
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| 11. |
- Ning, Lixin, et al.
(författare)
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Dynamic intensity model calculation of vibronic oscillator strengths for Cs2NaNdCl6 : A molecular dynamics study
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:43, s. 21424-21429
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Tidskriftsartikel (refereegranskat)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.
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| 12. |
- Ning, Lixin, et al.
(författare)
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Theoretical study ofI-4(13/2) -> I-4(15/2) luminescence quenching by OH for LaF3 : Er3+ nanoparticles in solution
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:1
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Tidskriftsartikel (refereegranskat)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.
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