1,311 research outputs found
Sensitive SQUID magnetometry for studying nano-magnetism
The superconducting quantum interference device (SQUID) magnetometer is one
of the most sensitive experimental techniques to magnetically characterize
samples with high sensitivity. Here we present a detailed discussion of
possible artifacts and pitfalls characteristic for commercial SQUID
magnetometers. This includes intrinsic artifacts which stem from the inherent
design of the magnetometer as well as potential issues due to the user. We
provide some guidelines how to avoid and correct these, which is of particular
importance when the proper magnetization of nano-scale objects shall be
established in cases where its response is dwarfed by that of the substrate it
comes with, a situation frequently found in the field of nano-magnetism.Comment: 18 pages PRB style, 13 figures (1st and 3rd wrongly reproduced, ???
High yield fusion in a Staged Z-pinch
We simulate fusion in a Z-pinch; where the load is a xenon-plasma liner
imploding onto a deuterium-tritium plasma target and the driver is a 2 MJ, 17
MA, 95 ns risetime pulser. The implosion system is modeled using the dynamic,
2-1/2 D, radiation-MHD code, MACH2. During implosion a shock forms in the Xe
liner, transporting current and energy radially inward. After collision with
the DT, a secondary shock forms pre-heating the DT to several hundred eV.
Adiabatic compression leads subsequently to a fusion burn, as the target is
surrounded by a flux-compressed, intense, azimuthal-magnetic field. The
intense-magnetic field confines fusion -particles, providing an
additional source of ion heating that leads to target ignition. The target
remains stable up to the time of ignition. Predictions are for a neutron yield
of and a thermonuclear energy of 84 MJ, that is, 42 times
greater than the initial, capacitor-stored energy
Study of Chirality in the Two-Dimensional XY Spin Glass
We study the chirality in the Villain form of the XY spin glass in
two--dimensions by Monte Carlo simulations. We calculate the chiral-glass
correlation length exponent and find that
in reasonable agreement with
earlier studies. This indicates that the chiral and phase variables are
decoupled on long length scales and diverge as with {\em different}
exponents, since the spin-glass correlation length exponent was found, in
earlier studies, to be about 1.0.Comment: 4 pages. Latex file and 4 embedded postscript files are included in a
self-unpacking compressed tar file. A postscript version is available at
ftp://chopin.ucsc.edu/pub/xysg.p
Chaos and Universality in a Four-Dimensional Spin Glass
We present a finite size scaling analysis of Monte Carlo simulation results
on a four dimensional Ising spin glass. We study chaos with both coupling and
temperature perturbations, and find the same chaos exponent in each case. Chaos
is investigated both at the critical temperature and below where it seems to be
more efficient (larger exponent). Dimension four seems to be above the critical
dimension where chaos with temperature is no more present in the critical
region. Our results are consistent with the Gaussian and bimodal coupling
distributions being in the same universality class.Comment: 11 pages, including 6 postscript figures. Latex with revtex macro
Numerical Study of Spin and Chiral Order in a Two-Dimensional XY Spin Glass
The two dimensional XY spin glass is studied numerically by a finite size
scaling method at T=0 in the vortex representation which allows us to compute
the exact (in principle) spin and chiral domain wall energies. We confirm
earlier predictions that there is no glass phase at any finite T. Our results
strongly support the conjecture that both spin and chiral order have the same
correlation length exponent . We obtain preliminary results
in 3d.Comment: 4 pages, 2 figures, revte
- …