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

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

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

Five-Spin Supramolecule for Simulating Quantum Decoherence of Bell States

We report a supramolecule that contains five spins of two different types and with, crucially, two different and predictable interaction energies between the spins. The supramolecule is characterized, and the interaction energies are demonstrated by electron paramagnetic resonance (EPR) spectroscopy. Based on the measured parameters, we propose experiments that would allow this designed supramolecule to be used to simulate quantum decoherence in maximally entangled Bell states that could be used in quantum teleportation

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

NMR Study of Spin Dynamics in V\u3csub\u3e7\u3c/sub\u3eZn and V\u3csub\u3e7\u3c/sub\u3eNi Molecular Rings

We present a 1H NMR investigation of spin dynamics in to finite integer spin molecular nanomagnetic rings, namely V7Zn and V7Ni. This study could be put in correlation with the problem of Haldane gap in infinite integer spin chains. While V7Zn is an approximation of a homometallic broken chain due to the presence of s = 0 Zn2+ ion uncoupled from nearest neighbor V2+ s = 1 ions, the V7Ni compound constitutes an example of a closed periodical s = 1 heterometallic chain. From preliminary susceptibility measurements on single crystals and data analysis, the exchange coupling constant J/kB results in the order of few kelvin. At room temperature, the frequency behavior of the 1H NMR spin–lattice relaxation rate 1/T1 allowed to conclude that the spin–spin correlation function is similar to the one observed in semi-integer spin molecules, but with a smaller cutoff frequency. Thus, the high-T data can be interpreted in terms of, e.g., a Heisenberg model including spin diffusion. On the other hand, the behavior of 1/T1 vs temperature at different constant fields reveals a clear peak at temperature of the order of J/kB, qualitatively in agreement with the well-known Bloembergen–Purcell–Pound model and with previous results on semi-integer molecular spin systems. Consequently, one can suggest that for a small number N of interacting s = 1 ions (N = 8), the Haldane conjecture does not play a key role on spin dynamics, and the investigated rings still keep the quantum nature imposed mainly by the low number of magnetic centers, with no clear topological effect due to integer spins