601 research outputs found
Titanium diaphragm makes excellent amplitron cathode support
Cathode support structure designed around a titanium diaphragm prevents radial misalignment between the cathode and anode in amplitrons. The titanium exhibits low thermal conductivity, tolerates lateral thermal expansion of the cathode, and is a poor primary and secondary emission medium
Selection in Zea mays L. by inbred line appearance and testcross performance in low and high plant densities
The development of inbred lines and the search for their best hybrid combinations are the main bases of corn improvement in the United States. The most commonly used method for inbred development is to enforce self fertilization for several generations while practicing visual selection for the more highly heritable characteristics. During these generations, surviving stocks maintained on an ear-to-row basis become highly homozygous and highly homogeneous. Because\u27 evaluation for combining ability by using test-cross procedures is expensive, it is usually delayed until after three to five generations of visual selection. Visual selection for combining ability among inbred progenies is rarely emphasized because of the commonly held opinion that it is relatively ineffective. Regardless of the effectiveness of visual selection, total genetic variability will be reduced following each selection cycle, according to the principle that the variability of a sample is less than the variability of a population. If selection is effective, the reduction will be even greater because of the removal of undesired genes, but the mean of the selected lines will exceed the mean of the original population.
Early testing, as proposed by Jenkins ( 1935 ), takes advantage of evaluation for combining ability in the So generation of a maize population, or the F2 of a hybrid, before genes have been eliminated by selection and, therefore, when the genetic variability among individuals is at a maximum. Superior germ plasm, identified by early testing, need not face the hazard of several generations of random sampling as in visual selection. However, the considerable expense of testing restricts the size and, therefore, the genetic base of the original population
Simple model for 1/f noise
We present a simple stochastic mechanism which generates pulse trains
exhibiting a power law distribution of the pulse intervals and a
power spectrum over several decades at low frequencies with close to
one. The essential ingredient of our model is a fluctuating threshold which
performs a Brownian motion. Whenever an increasing potential hits the
threshold, is reset to the origin and a pulse is emitted. We show that
if increases linearly in time, the pulse intervals can be approximated
by a random walk with multiplicative noise. Our model agrees with recent
experiments in neurobiology and explains the high interpulse interval
variability and the occurrence of noise observed in cortical
neurons and earthquake data.Comment: 4 pages, 4 figure
Fundamental Limits of Classical and Quantum Imaging
Quantum imaging promises increased imaging performance over classical
protocols. However, there are a number of aspects of quantum imaging that are
not well understood. In particular, it has so far been unknown how to compare
classical and quantum imaging procedures. Here, we consider classical and
quantum imaging in a single theoretical framework and present general
fundamental limits on the resolution and the deposition rate for classical and
quantum imaging. The resolution can be estimated from the image itself. We
present a utility function that allows us to compare imaging protocols in a
wide range of applications.Comment: 4 pages, 3 figures; accepted for Physical Review Letters, with
updated title and fixed typo
Parity-dependent squeezing of light
A parity-dependent squeezing operator is introduced which imposes different
SU(1,1) rotations on the even and odd subspaces of the harmonic oscillator
Hilbert space. This operator is used to define parity-dependent squeezed states
which exhibit highly nonclassical properties such as strong antibunching,
quadrature squeezing, strong oscillations in the photon-number distribution,
etc. In contrast to the usual squeezed states whose and Wigner functions
are simply Gaussians, the parity-dependent squeezed states have much more
complicated and Wigner functions that exhibit an interesting interference
in phase space. The generation of these states by parity-dependent quadratic
Hamiltonians is also discussed.Comment: accepted for publication in J. Phys. A, LaTeX, 11 pages, 12 figures
(compressed PostScript, available at
http://www.technion.ac.il/~brif/graphics/pdss_graph ). More information on
http://www.technion.ac.il/~brif/science.htm
High-sensitivity imaging with multi-mode twin beams
Twin entangled beams produced by single-pass parametric down-conversion (PDC)
offer the opportunity to detect weak amount of absorption with an improved
sensitivity with respect to standard techniques which make use of classical
light sources. We propose a differential measurement scheme which exploits the
spatial quantum correlation of type II PDC to image a weak amplitude object
with a sensitivity beyond the standard quantum limit imposed by shot-noise.Comment: 13 pages, 8 figure
Polarization-sensitive quantum-optical coherence tomography
We set forth a polarization-sensitive quantum-optical coherence tomography
(PS-QOCT) technique that provides axial optical sectioning with
polarization-sensitive capabilities. The technique provides a means for
determining information about the optical path length between isotropic
reflecting surfaces, the relative magnitude of the reflectance from each
interface, the birefringence of the interstitial material, and the orientation
of the optical axis of the sample. PS-QOCT is immune to sample dispersion and
therefore permits measurements to be made at depths greater than those
accessible via ordinary optical coherence tomography. We also provide a general
Jones matrix theory for analyzing PS-QOCT systems and outline an experimental
procedure for carrying out such measurements.Comment: 15 pages, 5 figures, to appear in Physical Review
Single Cooper pair tunneling induced by non-classical microwaves
A mesoscopic Josephson junction interacting with a mode of non-classical
microwaves with frequency is considered. Squeezing of the
electromagnetic field drastically affects the dynamics of Cooper tunneling. In
particular, Bloch steps can be observed even when the microwaves are in the
squeezed vacuum state with {\em zero} average amplitude of the field . The interval between these steps is double in size in
comparison to the conventional Bloch steps.Comment: 8 pages, 2 figures are available upon request to:
[email protected]
Dynamics of a Quantum Control-Not Gate for an Ensemble of Four-Spin Molecules at Room Temperature
We investigate numerically a single-pulse implementation of a quantum
Control-Not (CN) gate for an ensemble of Ising spin systems at room
temperature. For an ensemble of four-spin ``molecules'' we simulate the
time-evolution of the density matrix, for both digital and superpositional
initial conditions. Our numerical calculations confirm the feasibility of
implementation of quantum CN gate in this system at finite temperature, using
electromagnetic -pulse.Comment: 7 pages 3 figure
Does the 1/f frequency-scaling of brain signals reflect self-organized critical states?
Many complex systems display self-organized critical states characterized by
1/f frequency scaling of power spectra. Global variables such as the
electroencephalogram, scale as 1/f, which could be the sign of self-organized
critical states in neuronal activity. By analyzing simultaneous recordings of
global and neuronal activities, we confirm the 1/f scaling of global variables
for selected frequency bands, but show that neuronal activity is not consistent
with critical states. We propose a model of 1/f scaling which does not rely on
critical states, and which is testable experimentally.Comment: 3 figures, 6 page
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