Resonant photon absorption and hole burning in Cr7Ni antiferromagnetic rings

Presented are magnetization measurements on a crystal of Cr7Ni antiferromagnetic rings. Irradiation with microwaves at frequencies between 1 and 10 GHz leads to observation of very narrow resonant photon absorption lines which are mainly broadened by hyperfin interactions. A two-pulse hole burning technique allowed us to estimate the characteristic energy diffusion time.Comment: 4 pages, 5 figure

Molecular engineering of antiferromagnetic rings for quantum computation

The substitution of one metal ion in a Cr-based molecular ring with dominant antiferromagnetic couplings allows to engineer its level structure and ground-state degeneracy. Here we characterize a Cr7Ni molecular ring by means of low-temperature specific-heat and torque-magnetometry measurements, thus determining the microscopic parameters of the corresponding spin Hamiltonian. The energy spectrum and the suppression of the leakage-inducing S-mixing render the Cr7Ni molecule a suitable candidate for the qubit implementation, as further substantiated by our quantum-gate simulations.Comment: To appear in Physical Review Letter

Spin dynamics of heterometallic Cr7M wheels (M = Mn, Zn, Ni) probed by inelastic neutron scattering

Inelastic neutron scattering has been applied to the study of the spin dynamics of Cr-based antiferromagnetic octanuclear rings where a finite total spin of the ground state is obtained by substituting one Cr(III) ion (s = 3/2) with Zn (s = 0), Mn (s = 5/2) or Ni (s = 1) di-cations. Energy and intensity measurements for several intra-multiplet and inter-multiplet magnetic excitations allow us to determine the spin wavefunctions of the investigated clusters. Effects due to the mixing of different spin multiplets have been considered. Such effects proved to be important to correctly reproduce the energy and intensity of magnetic excitations in the neutron spectra. On the contrary to what is observed for the parent homonuclear Cr8 ring, the symmetry of the first excited spin states is such that anticrossing conditions with the ground state can be realized in the presence of an external magnetic field. Heterometallic Cr7M wheels are therefore good candidates for macroscopic observations of quantum effects.Comment: 9 pages, 11 figures, submitted to Phys. Rev. B, corrected typos and added references, one sentence change

Sliding resistance of grounded spray ice islands

In the 1970\u2019s and 1980\u2019s, a number of grounded ice islands were used as drilling platforms in the Beaufort Sea. These islands were constructed by spraying sea water into the air to form ice, gradually building up a large platform area that eventually grounded on the seabed. One important factor in the feasibility of using ice in such a manner concerns the sliding resistance of the grounded spray ice. Reports and papers from ice islands, relief well ice pads and spray ice barriers were studied in detail. This study provides both qualitative and quantitative knowledge on the sliding resistance of grounded spray ice structures. It illustrates that these structures were very stable with respect to seabed sliding.NRC publication: Ye

Development of a database for iceberg sightings off Canada's East Coast

Icebergs are a significant hazard for shipping and other operations conducted off Canada's east coast, such as oil drilling. Iceberg sightings have been made for almost 400 years. Currently, iceberg sightings are carried out by the International Ice Patrol, the Canadian Ice Service, and the offshore oil industry. Over the past seven years, a database has been developed which contains these sighting data. The paper describes the database and a summary of the data. Efforts are currently underway to expand the database with flight track information to increase the utility of the database by enabling iceberg spatial densities to be calculated, as it is not feasible to perform continuous sampling of the vast areas of interest. Sample results are presented.NRC publication: Ye

Ice decay boundaries for the ice regime system : Recommendations from a scientific analysis

The Canadian Ice Regime System takes into account the decay of sea ice by allowing the addition of +1 to the Ice Multiplier for ice that is deemed to be decayed. The AIRSS definition of decay relates to the surface properties of the ice such that decayed ice is defined as ice that has thaw holes or is at the "rotten" stage. This report examines this approach based on an analysis of the strength of first-year sea ice, second-year sea ice, multi-year sea ice, and the damage statistics for Arctic vessels. The analysis shows that there is no quantitative scientific basis for the current AIRSS approach of taking into account the decay of sea ice in the Ice Regime System. The analysis further shows that the decay of sea ice can be quantified in a meaningful manner. The report provides a detailed discussion of the analysis with recommendations for modifying AIRSS to account for the decay of sea ice.Le Syst\ue8me des r\ue9gimes de glaces du Canada tient compte de la d\ue9croissance de la glace de mer en permettant l\u2019ajout de +1 au Coefficient multiplicateur pour la glace jug\ue9e en d\ue9croissance. Dans le SRGNA, la d\ue9finition de la d\ue9croissance r\ue9f\ue8re aux propri\ue9t\ue9s de la surface de la glace et la glace en d\ue9croissance est d\ue9crite comme pr\ue9sentant des trous de fonte ou se situant au stade de glace \uabpourrie\ubb. Dans ce rapport on examine cette approche en fonction d\u2019une analyse de la r\ue9sistance de la glace de mer de premi\ue8re ann\ue9e, de la glace de mer de deuxi\ue8me ann\ue9e, de la glace de mer de plusieurs ann\ue9es et de statistiques sur les dommages caus\ue9s aux navires arctiques. L\u2019analyse montre que l\u2019actuelle approche pr\ue9conis\ue9e dans le SRGNA pour tenir compte de la d\ue9croissance de la glace de mer dans le Syst\ue8me des r\ue9gimes de glaces n\u2019a aucun fondement scientifique quantitatif. Elle montre en outre que la d\ue9croissance de la glace de mer peut \ueatre quantifi\ue9e de mani\ue8re sens\ue9e. Le rapport comprend une discussion d\ue9taill\ue9e de l\u2019analyse et des recommandations de modification du SRGNA permettant de tenir compte de la d\ue9croissance de la glace de mer.NRC publication: Ye

Numerical Simulation of Broken Ice Cover Forces on Structures: a Parametric Study

A numerical model of river ice interaction with bridge piers is presented. The model is based on a Particle-In-Cell (PIC) approach combined with a viscous plastic ice rheology. The plastic yield follows a Mohr-Coulomb criterion. The Zhang-Hibler (1997) numerical scheme is used to solve the momentum equations. The model is used in this paper to examine the role of the shape of the structure, ice thickness, ice properties, and velocity on the resulting ice forces. The results show good agreement with field measurements.NRC publication: Ye

Oxo-centered carboxylate-bridged trinuclear complexes deposited on Au(111) by a mass-selective electrospray.

We developed an apparatus for nondestructive in vacuum deposition of mass-selected fragile Cr based metal trinuclear complexes, by modifying a commercial Mass Spectrometer containing an electrospray ionization source. Starting from a solution, this system creates a beam of ionized molecules which is then transferred into an evacuated region where the molecules can be mass selected before deposition. To verify the system efficiency, we deposited sub monolayers of oxo-centered carboxylate-bridged trinuclear complexes (Cr3 and Cr2Ni) on Au(111) surface. By XPS and STM we determined the deposited molecule stoichiometry and the surface coverage. The results show that this apparatus is works well for the in vacuum deposition of molecular nanomagnets and, thanks to its reduced dimensions, it is portable