538 research outputs found
The boiling suppression of liquid nitrogen
When He gas is injected from room temperature into boiling liquid N,
boiling is suppressed, leaving liquid surface flat like a mirror. Although the
qualitative explanation for this phenomenon is known [Minkoff G J \textit{et
al}. Nature 1957;180(4599):1413-4.], it has not been studied quantitatively and
comprehensively yet. In this report, we made careful simultaneous measurements
of temperature and weight variation of the liquid. The results clearly indicate
that the boiling suppression is caused by cooling of the liquid with "internal
evaporation" of N into the He bubbles.Comment: 14 pages, 7 figure
Determination of the mosaic angle distribution of Grafoil platelets using continuous-wave NMR spectra
We described details of a method to estimate with good accuracy the mosaic
angle distributions of microcrystallites (platelets) in exfoliated graphite
like Grafoil which is commonly used as an adsorption substrate for helium thin
films. The method is based on analysis of resonance field shifts in
continuous-wave (CW) NMR spectra of He ferromagnetic monolayers making
use of the large nuclear polarization of the adsorbate itself. The mosaic angle
distribution of a Grafoil substrate analyzed in this way can be well fitted to
a gaussian form with a deg spread. This distribution is quite
different from the previous estimation based on neutron scattering data which
showed an unrealistically large isotropic powder-like component.Comment: 6 pages, 5 figure
Valence and Na content dependences of superconductivity in NaxCoO2.yH2O
Various samples of sodium cobalt oxyhydrate with relatively large amounts of
Na ions were synthesized by a modified soft-chemical process in which a
NaOH aqueous solution was added in the final step of the procedure. From these
samples, a superconducting phase diagram was determined for a section of a
cobalt valence of +3.48, which was compared with a previously obtained
one of +3.40. The superconductivity was significantly affected by the
isovalent exchanger of Na and HO, rather than by variation of
Co valence, suggesting the presence of multiple kinds of Fermi surface.
Furthermore, the high-field magnetic susceptibility measurements for one sample
up to 30 T indicated an upper critical field much higher than the Pauli limit
supporting the validity of the spin-triplet pairing mechanism.Comment: 4 figures and 1 tabl
Single-ion anisotropy in Haldane chains and form factor of the O(3) nonlinear sigma model
We consider spin-1 Haldane chains with single-ion anisotropy, which exists in
known Haldane chain materials. We develop a perturbation theory in terms of
anisotropy, where magnon-magnon interaction is important even in the low
temperature limit. The exact two-particle form factor in the O(3) nonlinear
sigma model leads to quantitative predictions on several dynamical properties
including dynamical structure factor and electron spin resonance frequency
shift. These agree very well with numerical results, and with experimental data
on the Haldane chain material Ni(CHN)N(PF)
Finite element analysis of magnetic circuits composed of axisymmetric and rectangular regions
A new approximate method is developed for calculating three-dimensional magnetic fields in magnetic circuits composed of connected axisymmetric and rectangular regions. Using this new method, fairly accurate solutions can be obtained when the leakage flux from the magnetic circuit is small. In this paper, the new method is explained and then the usefulness of the technique is clarified by comparing calculated and measured flux densities.</p
Nonaxisymmetric Magnetorotational Instability in Proto-Neutron Stars
We investigate the stability of differentially rotating proto-neutron stars
(PNSs) with a toroidal magnetic field. Stability criteria for nonaxisymmetric
MHD instabilities are derived using a local linear analysis. PNSs are expected
to have much stronger radial shear in the rotation velocity compared to normal
stars. We find that nonaxisymmetric magnetorotational instability (NMRI) with a
large azimuthal wavenumber is dominant over the kink mode () in
differentially rotating PNSs. The growth rate of the NMRI is of the order of
the angular velocity which is faster than that of the kink-type
instability by several orders of magnitude. The stability criteria are
analogous to those of the axisymmetric magnetorotational instability with a
poloidal field, although the effects of leptonic gradients are considered in
our analysis. The NMRI can grow even in convectively stable layers if the
wavevectors of unstable modes are parallel to the restoring force by the
Brunt-V\"ais\"al\"a oscillation. The nonlinear evolution of NMRI could amplify
the magnetic fields and drive MHD turbulence in PNSs, which may lead to
enhancement of the neutrino luminosity.Comment: 24pages, 7figures, Accepted for publication in the Astrophysical
Journal (December 12, 2005
Evidence for a Self-Bound Liquid State and the Commensurate-Incommensurate Coexistence in 2D He on Graphite
We made heat-capacity measurements of two dimensional (2D) He adsorbed on
graphite preplated with monolayer He in a wide temperature range (0.1 80 mK) at densities higher than that for the 4/7 phase (= 6.8
nm). In the density range of 6.8 8.1 nm, the 4/7
phase is stable against additional He atoms up to 20% and they are promoted
into the third layer. We found evidence that such promoted atoms form a
self-bound 2D Fermi liquid with an approximate density of 1 nm from the
measured density dependence of the -coefficient of heat capacity. We
also show evidence for the first-order transition between the commensurate 4/7
phase and the ferromagnetic incommensurate phase in the second layer in the
density range of 8.1 9.5 nm.Comment: 6 pages, 4 figure
Numerical analysis of antenna by a surface patch modeling
A cylindrical dipole antenna is numerically analyzed by the moment method. The surface of the antenna is approximated by triangular patches and the electric field integral equation is used for direct calculation of the surface current distribution. Therefore, the cylinder antenna can be treated in open or closed boundary form. The current expansion functions and the testing functions of the electric field boundary condition are of the triangular type. The surface integrals are numerically solved by a 33-point Gaussian quadrature approximation. The current distribution on a flat plate illuminated by a plane wave and the input admittance of a hollow cylindrical dipole as the near field quantities has been investigated. The convergence of the input admittance against the number of the triangular patches is presented, and the admittance solution is compared with the thin-wire approximation and theoretical results. Finally the CPU time and memory storage size for different numbers of patches are presented. Rapid admittance convergence and few required unknowns per square wavelength are the advantages of surface patch modeling </p
Anti-self-dual Maxwell solutions on hyperk\"ahler manifold and N=2 supersymmetric Ashtekar gravity
Anti-self-dual (ASD) Maxwell solutions on 4-dimensional hyperk\"ahler
manifolds are constructed. The N=2 supersymmetric half-flat equations are
derived in the context of the Ashtekar formulation of N=2 supergravity. These
equations show that the ASD Maxwell solutions have a direct connection with the
solutions of the reduced N=2 supersymmetric ASD Yang-Mills equations with a
special choice of gauge group. Two examples of the Maxwell solutions are
presented.Comment: 9 page
- …