Influence of central venous pressure upon sinus node responses to arterial baroreflex stimulation in man

Measurements were made of sinus node responses to arterial baroreceptor stimulation with phenylephrine injection or neck suction, before and during changes of central venous pressure provoked by lower body negative pressure or leg and lower truck elevation. Variations of central venous pressure between 1.1 and 9.0 mm Hg did not influence arterial baroreflex mediated bradycardia. Baroreflex sinus node responses were augmented by intravenous propranolol, but the level of responses after propranolol was comparable during the control state, lower body negative pressure, and leg and trunk elevation. Sinus node responses to very brief baroreceptor stimuli applied during the transitions of central venous pressure also were comparable in the three states. The authors conclude that physiological variations of central venous pressure do not influence sinus node responses to arterial baroreceptor stimulation in man

Magnetic ground state of pyrochlore oxides close to metal-insulator boundary probed by muon spin rotation

Magnetism of ruthernium pyrochlore oxides A2Ru2O7 (A = Hg, Cd, Ca), whose electronic properties within a localized ion picture are characterized by non-degenerate t2g orbitals (Ru5+, 4d3) and thereby subject to geometrical frustration, has been investigated by muon spin rotation/relaxation (muSR) technique. The A cation (mostly divalent) was varied to examine the effect of covalency (Hg > Cd > Ca) on their electronic property. In a sample with A = Hg that exhibits a clear metal-insulator (MI) transition below >> 100 K (which is associated with a weak structural transition), a nearly commensurate magnetic order is observed to develop in accordance with the MI transition. Meanwhile, in the case of A = Cd where the MI transition is suppressed to the level of small anomaly in the resistivity, the local field distribution probed by muon indicates emergence of a certain magnetic inhomogeneity below {\guillemotright} 30 K. Moreover, in Ca2Ru2O7 that remains metallic, we find a highly inhomogeneous local magnetism below >>25 K that comes from randomly oriented Ru moments and thus described as a "frozen spin liquid" state. The systematic trend of increasing randomness and itinerant character with decreasing covalency suggests close relationship between these two characters. As a reference for the effect of orbital degeneracy and associated Jahn-Teller instability, we examine a tetravalent ruthernium pyrochlore, Tl2Ru2O7 (Ru4+, 4d4), where the result of muSR indicates a non-magnetic ground state that is consistent with the formation of the Haldane chains suggested by neutron diffraction experiment.Comment: 12 pages, 13 figure

A deterministic alternative to the full configuration interaction quantum Monte Carlo method

Development of exponentially scaling methods has seen great progress in tackling larger systems than previously thought possible. One such technique, full configuration interaction quantum Monte Carlo, is a useful algorithm that allows exact diagonalization through stochastically sampling determinants. The method derives its utility from the information in the matrix elements of the Hamiltonian, along with a stochastic projected wave function, to find the important parts of Hilbert space. However, the stochastic representation of the wave function is not required to search Hilbert space efficiently, and here we describe a highly efficient deterministic method to achieve chemical accuracy for a wide range of systems, including the difficult Cr$_{2}$ dimer. In addition our method also allows efficient calculation of excited state energies, for which we illustrate with benchmark results for the excited states of C$_{2}$.Comment: 4 pages, 2 figure

Measurement on properties of MPPC for TOF-PET system

A large number of techniques are rapidly being developed for the diagnosis of cancer, including time-of-flight positron-emission tomography (TOF- PET). To construct an effective TOF-PET system, we introduced lutetium fine silicate (LFS) as a scintillator and a multi-pixel photon counter (MPPC) as a photosensor that exhibits a rapid response. In this study, we investigated four types of MPPCs with a sensitive area of 1 x 1 mm(2) sensitive area and different pitch sizes. All MPPCs showed a timing resolution of 72 ps at the full-width at half-maximum with operating voltages of dV similar to 3 V (with the exception of the 100-pixels MPPC).ArticleJOURNAL OF INSTRUMENTATION. 8:P02018 (2013)journal articl

Next-generation PET capability with lutetium fine silicate and multi-pixel photon counter

Currently, positron emission tomography (PET) systems are rapidly developing owing to the invention of new scintillators and photosensors, which contribute to construction of clearer and high-resolution images in cancer diagnosis. In this study, we used a Lutetium Fine Silicate (LFS) inorganic scintillator and multi-pixel photon counter (MPPC) as a photosensor. This combination is realistic for next-generation PET systems. These devices were directly coupled to form a unit detector. A pair of detector units was placed face-to-face, and they simultaneously detected annihilation gamma rays, assuming a pair detector in the PET system. A timing resolution of 96 ps in full width at half maximum (FWHM) was obtained. This result is almost the fastest timing resolution ever achieved. A good timing resolution contributes to noise reduction that leads to clear images. Furthermore, a spatial resolution of 1.9 mm in FWHM was obtained, which is sufficient to meet the spatial resolution requirements for next-generation PET systems.ArticleJOURNAL OF INSTRUMENTATION. 7:P10014 (2012)journal articl

Higher order approximation of isochrons

Phase reduction is a commonly used techinque for analyzing stable oscillators, particularly in studies concerning synchronization and phase lock of a network of oscillators. In a widely used numerical approach for obtaining phase reduction of a single oscillator, one needs to obtain the gradient of the phase function, which essentially provides a linear approximation of isochrons. In this paper, we extend the method for obtaining partial derivatives of the phase function to arbitrary order, providing higher order approximations of isochrons. In particular, our method in order 2 can be applied to the study of dynamics of a stable oscillator subjected to stochastic perturbations, a topic that will be discussed in a future paper. We use the Stuart-Landau oscillator to illustrate the method in order 2