Vesignieite BaCu3V2O8(OH)2 as a Candidate Spin-1/2 Kagome Antiferromagnet

A polycrystalline sample of vesignieite BaCu3V2O8(OH)2 comprising a nearly ideal kagome lattice composed of Cu2+ ions carrying spin 1/2 has been synthesized and studied by magnetization and heat capacity measurements. Magnetic susceptibility shows a neither long range order, a spin glass transition nor a spin gap down to 2 K, in spite of a moderately strong antiferromagnetic interaction of J/kB = 53 K between nearest-neighbor spins. A broad peak observed at a temperature corresponding to 0.4J in intrinsic magnetic susceptibility indicates a marked development of the short-range order. The ground state of vesignieite is probably a gapless spin liquid or is accompanied by a very small gap less than J/30.Comment: 4 pages, 5 figure

Electromagnetic Tracking in High Dose Rate Brachytherapy - A Composite Analysis Model

Electromagnetic tracking (EMT) in high dose rate Brachytherapy has to face a number of signal processing challenges which we summarize in this study. We propose a coherent signal processing chain which encompasses a particle filter tracking of the state space trajectory of the sensors inside catheters implanted surgically into the breast of female patients. Singular spectrum analysis is employed to remove high amplitude artifact signals from the recordings as well as to decompose simultaneously recorded signals from additional fiducial sensors used to monitor breathing motions. Ensemble empirical mode decomposition is applied to both, the fiducial and solenoid sensor signals to decompose them into their intrinsic modes. Information-theoretic similarity measures serve to identify those intrinsic modes which carry information about the breathing mode contamination of the observed solenoid sensor signals. Finally, a multi-dimensional scaling achieves a common principal coordinate system where both, the various EMT signals and related data deduced from an initial X-ray CT imaging can be compared quantitatively to identify any deviations from the treatment plan established with the CT data. We also consider the distributions of such deviations and demonstrate their heavy-tailed character. A Hartigan dip test is employed to establish a uni- or bi-modal character of these distributions which we approximate by alpha-stable distributions

High-Field ESR Measurements of S=1/2 Kagome Lattice Antiferromagnet BaCu3_3V2_2O8_8(OH)2_2

High-field electron spin resonance (ESR) measurements have been performed on vesignieite BaCu$_3$V$_2$O$_8$(OH)$_2$, which is considered as a nearly ideal model substance of $S$=1/2 kagome antiferromagnet, in the temperature region from 1.9 to 265 K. The frequency region is from 60 to 360 GHz and the applied pulsed magnetic field is up to 16 T. Observed g-value and linewidth show the increase below 20 K, which suggest the development of the short range order. Moreover, a gapless spin liquid ground state is suggested from the frequency-field relation at 1.9 K.Comment: 5 pages, 6 figures, jpsj2 class file, to be published in J. Phys. Soc. Jp

A tool to automatically analyze electromagnetic tracking data from high dose rate brachytherapy of breast cancer patients

During High Dose Rate Brachytherapy (HDR-BT) the spatial position of the radiation source inside catheters implanted into a female breast is determined via electromagnetic tracking (EMT). Dwell positions and dwell times of the radiation source are established, relative to the patient's anatomy, from an initial X-ray-CT-image. During the irradiation treatment, catheter displacements can occur due to patient movements. The current study develops an automatic analysis tool of EMT data sets recorded with a solenoid sensor to assure concordance of the source movement with the treatment plan. The tool combines machine learning techniques such as multi-dimensional scaling (MDS), ensemble empirical mode decomposition (EEMD), singular spectrum analysis (SSA) and particle filter (PF) to precisely detect and quantify any mismatch between the treatment plan and actual EMT measurements. We demonstrate that movement artifacts as well as technical signal distortions can be removed automatically and reliably, resulting in artifact-free reconstructed signals. This is a prerequisite for a highly accurate determination of any deviations of dwell positions from the treatment plan

Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9

We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK