Spin Waves in the Ferromagnetic Ground State of the Kagome Staircase System Co3V2O8

Inelastic neutron scattering measurements were performed on single crystal Co3V2O8 wherein magnetic cobalt ions reside on distinct spine and cross-tie sites within kagome staircase planes. This system displays a rich magnetic phase diagram which culminates in a ferromagnetic ground state below Tc~6 K. We have studied the low-lying magnetic excitations in this phase within the kagome plane. Despite the complexity of the system at higher temperatures, linear spin-wave theory describes most of the quantitative detail of the inelastic neutron measurements. Our results show two spin-wave branches, the higher energy of which displays finite spin-wave lifetimes well below Tc, and negligible magnetic exchange coupling between Co moments on the spine sites.Comment: 4 pages and 4 figure

Magnetic phase diagrams of the Kagome staircase compound Co3V2O8

At zero magnetic field, a series of five phase transitions occur in Co3V2O8. The Neel temperature, TN=11.4 K, is followed by four additional phase changes at T1=8.9 K, T2=7.0 K, T3=6.9 K, and T4=6.2 K. The different phases are distinguished by the commensurability of the b-component of its spin density wave vector. We investigate the stability of these various phases under magnetic fields through dielectric constant and magnetic susceptibility anomalies. The field-temperature phase diagram of Co3V2O8 is completely resolved. The complexity of the phase diagram results from the competition of different magnetic states with almost equal ground state energies due to competing exchange interactions and frustration.Comment: Proceedings of the 2007 Conference on Strongly Correlated Electron Systems, 2 pages, 2 figure

Borazineâ CF3â Adducts for Rapid, Room Temperature, and Broad Scope Trifluoromethylation

A fluoroformâ derived borazine CF3â transfer reagent is used to effect rapid nucleophilic reactions in the absence of additives, within minutes at 25â °C. Inorganic electrophiles spanning seven groups of the periodic table can be trifluoromethylated in high yield, including transition metals used for catalytic trifluoromethylation. Organic electrophiles included (hetero)arenes, enabling Câ H and Câ X trifluoromethylation reactions. Mechanistic analysis supports a dissociative mechanism for CF3â transfer, and cation modification afforded a reagent with enhanced stability.Von Fluoroform abgeleitet wurde ein stabiles Reagenz für nukleophile Trifluormethylierungen anorganischer und organischer Elektrophile (E) bei Raumtemperatur. Das Reaktionsspektrum umfasst 18 anorganische Elemente, nucleophile aromatische Substitutionen sowie CF3â â Additionen an Carbonylverbindungen und Imine. Kinetische Studien sprechen für einen dissoziativen Mechanismus.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141871/1/ange201711316-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141871/2/ange201711316.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141871/3/ange201711316_am.pd

Borazineâ CF3â Adducts for Rapid, Room Temperature, and Broad Scope Trifluoromethylation

A fluoroformâ derived borazine CF3â transfer reagent is used to effect rapid nucleophilic reactions in the absence of additives, within minutes at 25â °C. Inorganic electrophiles spanning seven groups of the periodic table can be trifluoromethylated in high yield, including transition metals used for catalytic trifluoromethylation. Organic electrophiles included (hetero)arenes, enabling Câ H and Câ X trifluoromethylation reactions. Mechanistic analysis supports a dissociative mechanism for CF3â transfer, and cation modification afforded a reagent with enhanced stability.A trifluoromethylating matter: A stable fluoroformâ derived reagent facilitates the nucleophilic trifluoromethylation of a broad array of inorganic and organic electrophiles (E) at room temperature. The reaction scope includes 18 inorganic elements, nucleophilic aromatic substitution, and CF3â addition to carbonyl and imine compounds. Kinetic analysis supports a dissociative mechanism.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141342/1/anie201711316_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141342/2/anie201711316.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141342/3/anie201711316-sup-0001-misc_information.pd

Scattering series in mobility problem for suspensions

The mobility problem for suspension of spherical particles immersed in an arbitrary flow of a viscous, incompressible fluid is considered in the regime of low Reynolds numbers. The scattering series which appears in the mobility problem is simplified. The simplification relies on the reduction of the number of types of single-particle scattering operators appearing in the scattering series. In our formulation there is only one type of single-particle scattering operator.Comment: 11 page

Pearling: stroke segmentation with crusted pearl strings

We introduce a novel segmentation technique, called Pearling, for the semi-automatic extraction of idealized models of networks of strokes (variable width curves) in images. These networks may for example represent roads in an aerial photograph, vessels in a medical scan, or strokes in a drawing. The operator seeds the process by selecting representative areas of good (stroke interior) and bad colors. Then, the operator may either provide a rough trace through a particular path in the stroke graph or simply pick a starting point (seed) on a stroke and a direction of growth. Pearling computes in realtime the centerlines of the strokes, the bifurcations, and the thickness function along each stroke, hence producing a purified medial axis transform of a desired portion of the stroke graph. No prior segmentation or thresholding is required. Simple gestures may be used to trim or extend the selection or to add branches. The realtime performance and reliability of Pearling results from a novel disk-sampling approach, which traces the strokes by optimizing the positions and radii of a discrete series of disks (pearls) along the stroke. A continuous model is defined through subdivision. By design, the idealized pearl string model is slightly wider than necessary to ensure that it contains the stroke boundary. A narrower core model that fits inside the stroke is computed simultaneously. The difference between the pearl string and its core contains the boundary of the stroke and may be used to capture, compress, visualize, or analyze the raw image data along the stroke boundary

Influence of Hydrodynamic Interactions on Mechanical Unfolding of Proteins

We incorporate hydrodynamic interactions in a structure-based model of ubiquitin and demonstrate that the hydrodynamic coupling may reduce the peak force when stretching the protein at constant speed, especially at larger speeds. Hydrodynamic interactions are also shown to facilitate unfolding at constant force and inhibit stretching by fluid flows.Comment: to be published in Journal of Physics: Condensed Matte

Absolute positions of 6.7-GHz methanol masers

The ATCA, MERLIN and VLA interferometers were used to measure the absolute positions of 35 6.7 GHz methanol masers to subarcsecond or higher accuracy. Our measurements represent essential preparatory data for Very Long Baseline Interferometry, which can provide accurate parallax and proper motion determinations of the star-forming regions harboring the masers. Our data also allow associations to be established with infrared sources at different wavelengths. Our findings support the view that the 6.7 GHz masers are associated with the earliest phases of high-mass star formation.Comment: A&A accepted 29 pages, 6 figures, 5 table