8,401 research outputs found
STRUCTURAL CHANGES IN U.S. AGRICULTURE: IMPLICATIONS FOR SMALL FARMS
A descriptive analysis and a survey of literature were used in this assessment of the transformation of the structure of production agriculture. The changes in production agriculture have important implications for resource use, population distribution in rural communities, and the survival of small farms. The shifting structural change in production agriculture as a response to economic and technological adjustments is not a temporary phenomenon. The economic and natural base of agriculture will change toward greater capital intensity and concentration of ownership, and will raise public policy questions in relation to the survival of a large farm population.Small farms, Structural changes, Production agriculture, Farm Management,
Single-shot time-domain studies of spin-torque-driven switching in magnetic tunnel junctions
We report single-shot measurements of resistance versus time for thermally
assisted spin-torque-driven switching in magnetic tunnel junctions. We achieve
sufficient sensitivity to resolve the resistance signals leading up to
switching, including the variations between individual switching events.
Analyses of pre-switching thermal fluctuations allow detailed measurements of
coherence times and variations in magnetization precession amplitude. We find
that with a small in-plane hard-axis magnetic field the magnetization dynamics
are more spatially coherent than for the case of zero field.Comment: 13 pages, 4 figure
Getting just the Supersymmetric Standard Model at Intersecting Branes on the Z6-orientifold
In this paper, globally N=1 supersymmetric configurations of intersecting
D6-branes on the Z6-orientifold are discussed, involving also fractional
branes. It turns out rather miraculously that one is led almost automatically
to just ONE particular class of 5 stack models containing the SM gauge group,
which all have the same chiral spectrum. The further discussion shows that
these models can be understood as exactly the supersymmetric standard model
without any exotic chiral symmetric/antisymmetric matter. The superpartner of
the Higgs finds a natural explanation and the hypercharge remains massless.
However, the non-chiral spectrum within the model class is very different and
does not in all cases allow for a N=2 low energy field theoretical
understanding of the necessary breaking U(1)xU(1)->U(1) along the Higgs branch,
which is needed in order to get the standard Yukawa couplings. Also the
left-right symmetric models belong to exactly one class of chiral spectra,
where the two kinds of exotic chiral fields can have the interpretation of
forming a composite Higgs. The aesthetical beauty of these models, involving
only non-vanishing intersection numbers of an absolute value three, seems to be
unescapable.Comment: 45 pages, 2 figures, v3:some signs corrected in erratum, conclusions
unchange
Spin-Torque-Induced Rotational Dynamics of a Magnetic Vortex Dipole
We study, both experimentally and by numerical modeling, the magnetic
dynamics that can be excited in a magnetic thin-film nanopillar device using
the spin torque from a spatially localized current injected via a
10s-of-nm-diameter aperture. The current-driven magnetic dynamics can produce
large amplitude microwave emission at zero magnetic field, with a frequency
well below that of the uniform ferromagnetic resonance mode. Micromagnetic
simulations indicate that the physical origin of this efficient microwave
nano-oscillator is the nucleation and subsequent steady-state rotational
dynamics of a magnetic vortex dipole driven by the localized spin torque. These
results show this novel implementation of a spintronic nano-oscillator is a
promising candidate for microwave technology applications.Comment: 19 pages, 4 figures
Dual mode laser velocimeter
Described is a laser Doppler velocimeter (LDV) which is capable of operating with a small focus diameter for analyzing fluid flows at low velocity with high spatial resolution, or with a larger focus diameter to measure fluid flows at higher velocities accurately. More particularly, this is an LDV in which a simple reversal of a lens pair will allow it to operate in the two focus diameter modes
Coherent state LOQC gates using simplified diagonal superposition resource states
In this paper we explore the possibility of fundamental tests for coherent
state optical quantum computing gates [T. C. Ralph, et. al, Phys. Rev. A
\textbf{68}, 042319 (2003)] using sophisticated but not unrealistic quantum
states. The major resource required in these gates are state diagonal to the
basis states. We use the recent observation that a squeezed single photon state
() approximates well an odd superposition of coherent
states () to address the diagonal resource
problem. The approximation only holds for relatively small and hence
these gates cannot be used in a scaleable scheme. We explore the effects on
fidelities and probabilities in teleportation and a rotated Hadamard gate.Comment: 21 pages, 12 figure
Gilbert Damping in Conducting Ferromagnets II: Model Tests of the Torque-Correlation Formula
We report on a study of Gilbert damping due to particle-hole pair excitations
in conducting ferromagnets. We focus on a toy two-band model and on a four-band
spherical model which provides an approximate description of ferromagnetic
(Ga,Mn)As. These models are sufficiently simple that disorder-ladder-sum vertex
corrections to the long-wavelength spin-spin response function can be summed to
all orders. An important objective of this study is to assess the reliability
of practical approximate expressions which can be combined with electronic
structure calculations to estimate Gilbert damping in more complex systems.Comment: 10 pages, 10 figures. Submitted to Phys. Rev.
Linear Optical CNOT Gate in the Coincidence Basis
We describe the operation and tolerances of a non-deterministic, coincidence
basis, quantum CNOT gate for photonic qubits. It is constructed solely from
linear optical elements and requires only a two-photon source for its
demonstration.Comment: Submitted to Physical Review
Paramagnetic Breakdown of Superconductivity in Ultrasmall Metallic Grains
We study the magnetic-field-induced breakdown of superconductivity in
nm-scale metal grains having a mean electron level spacing (bulk gap). Using a generalized variational BCS approach that
yields good qualitative agreement with measured spectra, we argue that Pauli
paramagnetism dominates orbital diamagnetism, as in the case of thin films in a
parallel magnetic field. However, the first-order transition observed for the
latter can be made continuous by finite size effects. The mean-field procedure
of describing the system by a single pairing parameter breaks down for
.Comment: 4 pages of revtex, 3 postscript figures, uses psfrag.sty, epsfig.sty.
Slightly revised and improved version, matching published versio
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