8,072 research outputs found
Low energy proton bidirectional anisotropies and their relation to transient interplanetary magnetic structures: ISEE-3 observations
It is known that the interplanetary medium in the period approaching solar maximum is characterized by an enhancement in the occurrence of transient solar wind streams and shocks and that such systems are often associated with looplike magnetic structures or clouds. There is observational evidence that bidirectional, field aligned flows of low energy particles could be a signature of such looplike structures, although detailed models for the magnetic field configuration and injection mechanisms do not exist at the current time. Preliminary results of a survey of low energy proton bidirectional anisotropies measured on ISEE-3 in the interplanetary medium between August 1978 and May 1982, together with magnetic field data from the same spacecraft are presented
Evidence of columnar order in the fully frustrated transverse field Ising model on the square lattice
Using extensive classical and quantum Monte Carlo simulations, we investigate
the ground-state phase diagram of the fully frustrated transverse field Ising
model on the square lattice. We show that pure columnar order develops in the
low-field phase above a surprisingly large length scale, below which an
effective U(1) symmetry is present. The same conclusion applies to the Quantum
Dimer Model with purely kinetic energy, to which the model reduces in the
zero-field limit, as well as to the stacked classical version of the model. By
contrast, the 2D classical version of the model is shown to develop plaquette
order. Semiclassical arguments show that the transition from plaquette to
columnar order is a consequence of quantum fluctuations.Comment: 5 pages (including Supplemental Material), 5 figure
Pre-selectable integer quantum conductance of electrochemically fabricated silver point contacts
The controlled fabrication of well-ordered atomic-scale metallic contacts is
of great interest: it is expected that the experimentally observed high
percentage of point contacts with a conductance at non-integer multiples of the
conductance quantum G_0 = 2e^2/h in simple metals is correlated to defects
resulting from the fabrication process. Here we demonstrate a combined
electrochemical deposition and annealing method which allows the controlled
fabrication of point contacts with pre-selectable integer quantum conductance.
The resulting conductance measurements on silver point contacts are compared
with tight-binding-like conductance calculations of modeled idealized junction
geometries between two silver crystals with a predefined number of contact
atoms
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