8,067 research outputs found
Defining Attempts: Mandujano\u27s Error
The law of attempt requires a court to determine when trying to commit a crime is, in itself, conduct that deserves criminal punishment. Common-law courts were cautious not to push the boundaries of attempt crimes too far, and early definitions of attempt required that a defendant come very close to the completion of an intended crime before he could be convicted. As Congress has codified criminal law, it has created attempt statutes without defining attempt, presumably believing that courts would continue to use common-law meanings as they had always done. This is exactly what happened until the late twentieth century, when federal courts began to adopt a new, harsher formulation that had been proposed in the American Law Institute\u27s Model Penal Code (MPC). This Note examines the strange process through which federal courts expanded the definition of a background principle of criminal law, and argues that they were wrong to do so. Judges who ignore such deep common-law roots usurp the legislature\u27s role in defining crimes, and create confusion as to the true meaning of criminal statutes
Compression of Correlation Matrices and an Efficient Method for Forming Matrix Product States of Fermionic Gaussian States
Here we present an efficient and numerically stable procedure for compressing
a correlation matrix into a set of local unitary single-particle gates, which
leads to a very efficient way of forming the matrix product state (MPS)
approximation of a pure fermionic Gaussian state, such as the ground state of a
quadratic Hamiltonian. The procedure involves successively diagonalizing
subblocks of the correlation matrix to isolate local states which are purely
occupied or unoccupied. A small number of nearest neighbor unitary gates
isolates each local state. The MPS of this state is formed by applying the
many-body version of these gates to a product state. We treat the simple case
of compressing the correlation matrix of spinless free fermions with definite
particle number in detail, though the procedure is easily extended to fermions
with spin and more general BCS states (utilizing the formalism of Majorana
modes). We also present a DMRG-like algorithm to obtain the compressed
correlation matrix directly from a hopping Hamiltonian. In addition, we discuss
a slight variation of the procedure which leads to a simple construction of the
multiscale entanglement renormalization ansatz (MERA) of a fermionic Gaussian
state, and present a simple picture of orthogonal wavelet transforms in terms
of the gate structure we present in this paper. As a simple demonstration we
analyze the Su-Schrieffer-Heeger model (free fermions on a 1D lattice with
staggered hopping amplitudes).Comment: 15 pages, 17 figure
Characterization of low-energy magnetic excitations in chromium
The low-energy excitations of Cr, i.e. the Fincher-Burke (FB) modes, have
been investigated in the transversely polarized spin-density-wave phase by
inelastic neutron scattering using a single-(Q+-) crystal with a propagation
vector (Q+-) parallel to [0,0,1]. The constant-momentum-transfer scans show
that the energy spectra consist of two components, namely dispersive FB modes
and an almost energy-independent cross section. Most remarkably, we find that
the spectrum of the FB modes exhibits one peak at 140 K near Q = (0,0,0.98) and
two peaks near Q = (0,0,1.02), respectively. This is surprising because Cr
crystallizes in a centro-symmetric bcc structure. The asymmetry of those energy
spectra decreases with increasing temperature. In addition, the observed
magnetic peak intensity is independent of Q suggesting a transfer of
spectral-weight between the upper and lower FB modes. The energy-independent
cross section is localized only between the incommensurate peaks and develops
rapidly with increasing temperature.Comment: 6 pages, 8 figure
HEAO-A nominal scanning observation schedule
The HEAO-A observatory, scheduled for launch in late June 1977, will spend most of its orbital lifetime in a scanning mode, spining from 0.03 to 0.1 rpm about an axis aligned with the sun. The dates of availability in the scan band are given for a list of 248 X-ray sources. Celestial maps of source locations and scan planes, and examples of the nighttime elevation of available sources are presented. This document is intended to aid ground-based observers in planning coordinated observations with HEAO-A
Double Exchange in a Magnetically Frustrated System
This work examines the magnetic order and spin dynamics of a double-exchange
model with competing ferromagnetic and antiferromagnetic Heisenberg
interactions between the local moments. The Heisenberg interactions are
periodically arranged in a Villain configuration in two dimensions with
nearest-neighbor, ferromagnetic coupling and antiferromagnetic coupling
. This model is solved at zero temperature by performing a
expansion in the rotated reference frame of each local moment.
When exceeds a critical value, the ground state is a magnetically
frustrated, canted antiferromagnet. With increasing hopping energy or
magnetic field , the local moments become aligned and the ferromagnetic
phase is stabilized above critical values of or . In the canted phase, a
charge-density wave forms because the electrons prefer to sit on lines of sites
that are coupled ferromagnetically. Due to a change in the topology of the
Fermi surface from closed to open, phase separation occurs in a narrow range of
parameters in the canted phase. In zero field, the long-wavelength spin waves
are isotropic in the region of phase separation. Whereas the average spin-wave
stiffness in the canted phase increases with or , it exhibits a more
complicated dependence on field. This work strongly suggests that the jump in
the spin-wave stiffness observed in PrCaMnO with at a field of 3 T is caused by the delocalization of the electrons rather
than by the alignment of the antiferromagnetic regions.Comment: 28 pages, 12 figure
Spin Dynamics of Double-Exchange Manganites with Magnetic Frustration
This work examines the effects of magnetic frustration due to competing
ferromagnetic and antiferromagnetic Heisenberg interactions on the spin
dynamics of the double-exchange model. When the local moments are non-colinear,
a charge-density wave forms because the electrons prefer to sit on lines of
sites that are coupled ferromagnetically. With increasing hopping energy, the
local spins become aligned and the average spin-wave stiffness increases. Phase
separation is found only within a narrow range of hopping energies. Results of
this work are applied to the field-induced jump in the spin-wave stiffness
observed in the manganite PrCaMnO with .Comment: 10 pages, 3 figure
Spin Dynamics of a Canted Antiferromagnet in a Magnetic Field
The spin dynamics of a canted antiferromagnet with a quadratic spin-wave
dispersion near \vq =0 is shown to possess a unique signature. When the
anisotropy gap is negligible, the spin-wave stiffness \dsw (\vq, B) =
(\omega_{\vq}-B)/q^2 depends on whether the limit of zero field or zero
wavevector is taken first. Consequently, \dsw is a strong function of
magnetic field at a fixed wavevector. Even in the presence of a sizeable
anisotropy gap, the field dependence of both \dsw and the gap energy
distinguishes a canted antiferromagnet from a phase-separated mixture
containing both ferromagnetic and antiferromagnetic regions.Comment: 10 pages, 3 figure
Dynamical Mean-Field Study of the Ferromagnetic Transition Temperature of a Two-Band Model for Colossal Magnetoresistance Materials
The ferromagnetic (FM) transition temperature (Tc) of a two-band
Double-Exchange (DE) model for colossal magnetoresistance (CMR) materials is
studied using dynamical mean-field theory (DMFT), in wide ranges of coupling
constants, hopping parameters, and carrier densities. The results are shown to
be in excellent agreement with Monte Carlo simulations. When the bands overlap,
the value of Tc is found to be much larger than in the one-band case, for all
values of the chemical potential within the energy overlap interval. A nonzero
interband hopping produces an additional substantial increase of Tc, showing
the importance of these nondiagonal terms, and the concomitant use of multiband
models, to boost up the critical temperatures in DE-based theories.Comment: 4 pages, 4 eps figure
Short-Range Ordered Phase of the Double-Exchange Model in Infinite Dimensions
Using dynamical mean-field theory, we have evaluated the magnetic
instabilities and T=0 phase diagram of the double-exchange model on a Bethe
lattice in infinite dimensions. In addition to ferromagnetic (FM) and
antiferromagnetic (AF) phases, we also study a class of disordered phases with
magnetic short-range order (SRO). In the weak-coupling limit, a SRO phase has a
higher transition temperature than the AF phase for all fillings p below 1 and
can even have a higher transition temperature than the FM phase. At T=0 and for
small Hund's coupling J_H, a SRO state has lower energy than either the FM or
AF phases for 0.26\le p 0 limit
but appears for any non-zero value of J_H.Comment: 11 pages, 3 figures, published versio
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