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

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

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

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

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

Data collection program on ice regimes onboard the CCG icebreakers - 2003

A field program was designed and carried out onboard six Canadian Coast Guard icebreakers during the summer of 2003. Information was collected on the ice conditions (ice regimes) and the stage of melting (decay) of the ice. In total, 57 ice regimes were documented and photographed. Based on this information, the severity of the ice regimes were evaluated in terms of the Canadian Arctic Ice Regime Shipping System. This report provides a description of the data collection program and an overview of the results.Un programme de collecte de donn\ue9es sur le terrain \ue0 bord de six brise-glaces de la Garde c\uf4ti\ue8re canadienne a \ue9t\ue9 con\ue7u et ex\ue9cut\ue9 pendant l\u2019\ue9t\ue9 de 2003. On a recueilli de l\u2019information sur l\u2019\ue9tat des glaces (r\ue9gimes de glaces) et le stade de fonte (d\ue9croissance). Au total, 57 r\ue9gimes de glaces ont \ue9t\ue9 document\ue9s et photographi\ue9s. D\u2019apr\ue8s l\u2019information recueillie, la rigueur des r\ue9gimes de glaces a \ue9t\ue9 \ue9valu\ue9e en terme du Syst\ue8me des r\ue9gimes de glaces pour la navigation dans l'Arctique. Ce rapport pr\ue9sente une description du programme de collecte de donn\ue9es et une vue d\u2019ensemble des r\ue9sultats.NRC publication: Ye

Entanglement in supramolecular spin systems of two weakly coupled antiferromagnetic rings (purple-Cr7Ni)

International audienceWe characterize supramolecular magnetic structures, consisting of two weakly coupled antiferromagnetic rings, by low-temperature specific heat, susceptibility, magnetization and electron paramagnetic resonance measurements. Intra- and inter-ring interactions are modeled through a microscopic spin-Hamiltonian approach that reproduces all the experimental data quantitatively and legitimates the use of an effective two-qubit picture. Spin entanglement between the rings is experimentally demonstrated through magnetic susceptibility below 50 mK and theoretically quantified by the concurrence

Spin dynamics of molecular nanomagnets fully unraveled by four-dimensional inelastic neutron scattering

Molecular nanomagnets are among the first examples of spin systems of finite size and have been test-beds for addressing a range of elusive but important phenomena in quantum dynamics. In fact, for short-enough timescales the spin wavefunctions evolve coherently according to the an appropriate cluster spin-Hamiltonian, whose structure can be tailored at the synthetic level to meet specific requirements. Unfortunately, to this point it has been impossible to determine the spin dynamics directly. If the molecule is sufficiently simple, the spin motion can be indirectly assessed by an approximate model Hamiltonian fitted to experimental measurements of various types. Here we show that recently-developed instrumentation yields the four-dimensional inelastic-neutron scattering function S(Q,E) in vast portions of reciprocal space and enables the spin dynamics to be determined with no need of any model Hamiltonian. We exploit the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this new approach. For the first time we extract a model-free picture of the quantum dynamics of a molecular nanomagnet. This allows us, for example, to examine how a quantum fluctuation propagates along the ring and to directly test the degree of validity of the N\'{e}el-vector-tunneling description of the spin dynamics

On the possibility of magneto-structural correlations: detailed studies of di-nickel carboxylate complexes

A series of water-bridged dinickel complexes of the general formula [Ni<sub>2</sub>(μ<sub>2</sub>-OH<sub>2</sub>)(μ2- O<sub>2</sub>C<sup>t</sup>Bu)<sub>2</sub>(O<sub>2</sub>C<sup>t</sup>Bu)2(L)(L0)] (L = HO<sub>2</sub>C<sup>t</sup>Bu, L0 = HO<sub>2</sub>C<sup>t</sup>Bu (1), pyridine (2), 3-methylpyridine (4); L = L0 = pyridine (3), 3-methylpyridine (5)) has been synthesized and structurally characterized by X-ray crystallography. The magnetic properties have been probed by magnetometry and EPR spectroscopy, and detailed measurements show that the axial zero-field splitting, D, of the nickel(ii) ions is on the same order as the isotropic exchange interaction, J, between the nickel sites. The isotropic exchange interaction can be related to the angle between the nickel centers and the bridging water molecule, while the magnitude of D can be related to the coordination sphere at the nickel sites

Recipes for spin-based quantum computing

Technological growth in the electronics industry has historically been measured by the number of transistors that can be crammed onto a single microchip. Unfortunately, all good things must come to an end; spectacular growth in the number of transistors on a chip requires spectacular reduction of the transistor size. For electrons in semiconductors, the laws of quantum mechanics take over at the nanometre scale, and the conventional wisdom for progress (transistor cramming) must be abandoned. This realization has stimulated extensive research on ways to exploit the spin (in addition to the orbital) degree of freedom of the electron, giving birth to the field of spintronics. Perhaps the most ambitious goal of spintronics is to realize complete control over the quantum mechanical nature of the relevant spins. This prospect has motivated a race to design and build a spintronic device capable of complete control over its quantum mechanical state, and ultimately, performing computations: a quantum computer. In this tutorial we summarize past and very recent developments which point the way to spin-based quantum computing in the solid-state. After introducing a set of basic requirements for any quantum computer proposal, we offer a brief summary of some of the many theoretical proposals for solid-state quantum computers. We then focus on the Loss-DiVincenzo proposal for quantum computing with the spins of electrons confined to quantum dots. There are many obstacles to building such a quantum device. We address these, and survey recent theoretical, and then experimental progress in the field. To conclude the tutorial, we list some as-yet unrealized experiments, which would be crucial for the development of a quantum-dot quantum computer.Comment: 45 pages, 12 figures (low-res in preprint, high-res in journal) tutorial review for Nanotechnology; v2: references added and updated, final version to appear in journa