Time-odd mean fields in covariant density functional theory: Rotating systems

Time-odd mean fields (nuclear magnetism) and their impact on physical observables in rotating nuclei are studied in the framework of covariant density functional theory (CDFT). It is shown that they have profound effect on the dynamic and kinematic moments of inertia. Particle number, configuration and rotational frequency dependences of their impact on the moments of inertia have been analysed in a systematic way. Nuclear magnetism can also considerably modify the band crossing features such as crossing frequencies and the properties of the kinematic and dynamic moments of inertia in the band crossing region. The impact of time-odd mean fields on the moments of inertia in the regions away from band crossing only weakly depends on the relativistic mean field parametrization, reflecting good localization of the properties of time-odd mean fields in CDFT. The moments of inertia of normal-deformed nuclei considerably deviate from the rigid body value. On the contrary, superdeformed and hyperdeformed nuclei have the moments of inertia which are close to rigid body value. The structure of the currents in rotating frame, their microscopic origin and the relations to the moments of inertia have been systematically analysed. The phenomenon of signature separation in odd-odd nuclei, induced by time-odd mean fields, has been analysed in detail.Comment: 20 pages. 16 figure

Time-odd mean fields in covariant density functional theory I. Non-rotating systems

Time-odd mean fields (nuclear magnetism) are analyzed in the framework of covariant density functional theory (CDFT). It is shown that they always provide additional binding to the binding energies of odd-mass nuclei. This additional binding only weakly depends on the RMF parametrization reflecting good localization of the properties of time-odd mean fields in CDFT. The underlying microscopic mechanism is discussed in detail. Time-odd mean fields affect odd-even mass differences. However, our analysis suggests that the modifications of the strength of pairing correlations required to compensate for their effects are modest. In contrast, time-odd mean fields have profound effect on the properties of odd-proton nuclei in the vicinity of proton-drip line. Their presence can modify the half-lives of proton-emitters (by many orders of magnitude in light nuclei) and affect considerably the possibilities of their experimental observation.Comment: 20 pages, 19 figure

Chondrocyte Deformations as a Function of Tibiofemoral Joint Loading Predicted by a Generalized High-Throughput Pipeline of Multi-Scale Simulations

Cells of the musculoskeletal system are known to respond to mechanical loading and chondrocytes within the cartilage are not an exception. However, understanding how joint level loads relate to cell level deformations, e.g. in the cartilage, is not a straightforward task. In this study, a multi-scale analysis pipeline was implemented to post-process the results of a macro-scale finite element (FE) tibiofemoral joint model to provide joint mechanics based displacement boundary conditions to micro-scale cellular FE models of the cartilage, for the purpose of characterizing chondrocyte deformations in relation to tibiofemoral joint loading. It was possible to identify the load distribution within the knee among its tissue structures and ultimately within the cartilage among its extracellular matrix, pericellular environment and resident chondrocytes. Various cellular deformation metrics (aspect ratio change, volumetric strain, cellular effective strain and maximum shear strain) were calculated. To illustrate further utility of this multi-scale modeling pipeline, two micro-scale cartilage constructs were considered: an idealized single cell at the centroid of a 100×100×100 μm block commonly used in past research studies, and an anatomically based (11 cell model of the same volume) representation of the middle zone of tibiofemoral cartilage. In both cases, chondrocytes experienced amplified deformations compared to those at the macro-scale, predicted by simulating one body weight compressive loading on the tibiofemoral joint. In the 11 cell case, all cells experienced less deformation than the single cell case, and also exhibited a larger variance in deformation compared to other cells residing in the same block. The coupling method proved to be highly scalable due to micro-scale model independence that allowed for exploitation of distributed memory computing architecture. The method’s generalized nature also allows for substitution of any macro-scale and/or micro-scale model providing application for other multi-scale continuum mechanics problems

INFRARED SPECTROSCOPY OF OCS CLUSTERS

Author Institution: Department of Physics and Astronomy, 2500 University Drive NW, Calgary,; Alberta T2N 1N4, Canada; Steacie Institute for Molecular Sciences, National Research Council of Canada,; Ottawa, Ontario K1A 0R6, CanadaPreviously, the non-polar lowest energy isomer of (OCS)$_2$ has been studied via infrared spectroscopy, while the polar form has only been deduced from qualitative beam ``refocusing" experiments. The spectrum and the structure of OCS trimer are known from mm-wave spectroscopy. Infrared spectra of the (OCS)$_2$, (OCS)$_3$ and (OCS)$_4$ van der Waals complexes have been studied in the region of the C-O stretching fundamental using a tunable diode laser to probe a pulsed supersonic slit jet. We have measured a new infrared band at 2069.3 cm$^{-1}$ and assigned it to the long-anticipated polar isomer of OCS dimer, helping to explain apparent discrepancies among earlier studies. A trimer band of OCS has also been assigned based on lower state combination differences. The upper state of this band is perturbed and the nature of the perturbations is not clear. Four other bands have also been observed and tentatively assigned to OCS tetramer. These bands are best described as an asymmetric top with an accidental spherical top structure. Isotopic studies of these bands are presently underway to clarify their origin

Isotope effects in the infrared spectrum of the OCS dimer

Infrared spectra of 34S and 13C isotopes of the OCS dimer are studied in the 2015-2075?cm-1 region using a tunable laser to probe a pulsed supersonic expansion. The spectrum of (16O12C34S)2 is similar to that of the normal isotope, but that of (16O13C32S)2 differs due to nuclear spin statistics and due to small (<0.01?cm-1) rotational perturbations whose nature is not entirely clear. The shift of the (16O13C32S)2 band origin relative to 16O13C32S is significantly smaller than predicted by scaling from the normal isotope. It was not possible to detect spectra of isotopically mixed dimers.NRC publication: Ye

Nitrous oxide dimer : observation of a new polar isomer

Spectra of the nitrous oxide dimer (N2O)2 are studied in the region of the N2O nu1 fundamental band around 2230 cm?1 using a rapid-scan tunable diode laser spectrometer to probe a pulsed supersonic jet expansion. The previously known band of the centrosymmetric nonpolar dimer is analyzed in improved detail, and a new band is observed and assigned to a polar isomer of (N2O)2. This polar form of the dimer has a slipped parallel structure, rather similar to the slipped antiparallel structure of the nonpolar form but with a slightly larger intermolecular distance. The accurate rotational parameters determined here should enable a microwave observation of the polar N2O dimer. The need for a modern ab initio investigation of the N2O\ufffdN2O intermolecular potential energy surface is emphasized.Peer reviewed: YesNRC publication: Ye