40,502 research outputs found
A new calibration method for time delay standard and its application
A method which is used to measure time delay accurately by using a Type 900-LB slotted line is described. The accuracy for calibrating time delay of a precision coaxial air line Type 900-L is about + or - (0.4 to 0.6)ps, and for coaxial cables with VSWR less than 1.5 and time delay t less than 50ns is about + or - (3 to 5)ps. Theoretical analysis and mathematical derivation of microwave networks in cascade are given. Methods to eliminate the errors which are caused by the discontinuities and the error analysis of the measuring system are presented. Skin effect analysis of the transient characteristic of coaxial transmission line are discussed in detail. Methods to eliminate the errors which result from using the calibrated time delay standard to calibrate time interval measurement instruments are presented. The estimation of errors and formulae for correction of those errors are described
On the equilibrium of the magnetopause current layer
Magnetopause current layer equilibriu
Numerical Study of the Correspondence Between the Dissipative and Fixed Energy Abelian Sandpile Models
We consider the Abelian sandpile model (ASM) on the large square lattice with
a single dissipative site (sink). Particles are added by one per unit time at
random sites and the resulting density of particles is calculated as a function
of time. We observe different scenarios of evolution depending on the value of
initial uniform density (height) . During the first stage of the
evolution, the density of particles increases linearly. Reaching a critical
density , the system changes its behavior sharply and relaxes
exponentially to the stationary state of the ASM with . We found
numerically that and . Our
observations suggest that the equality holds for more general
initial conditions with non-positive heights. In parallel with the ASM, we
consider the conservative fixed-energy Abelian sandpile model (FES). The
extensive Monte-Carlo simulations for have confirmed that in the
limit of large lattices coincides with the threshold density
of FES. Therefore, can be identified with
if the FES starts its evolution with non-positive uniform height .Comment: 6 pages, 8 figure
Hearing Conservation Program For Marching Band Members: A Risk For Noise-Induced Hearing Loss?
Purpose: To examine the risk for noise-induced hearing loss (NIHL) in university marching band members and to provide an overview of a hearing conservation program for a marching band. Method: Sound levels during band rehearsals were recorded and audiometric hearing thresholds and transient otoacoustic emission were measured over a 3-year period. Musician's earplugs and information about hearing loss were provided to the students. The hearing thresholds of other college students were tested as a partial control. Results: There were no significant differences in hearing thresholds between the two groups. During initial testing, more marching band members showed apparent high-frequency notches than control students. Follow-up hearing tests in a subsequent year for the marching band members showed that almost all notches disappeared. Persistent standard threshold shift (STS) across tests was not observed in the band members. Conclusion: Band members showed no evidence of STS or persistent notched audiograms. Because accepted procedures for measuring hearing showed a lack of precision in reliably detecting early NIHL in marching band members, it is recommended that signs of NIHL be sought in repeated measurements compared to baseline audiograms rather than in a single measure (a single notch). A hearing conservation program for this population is still recommended because of lengthy rehearsal times with high sound-level exposure during rehearsals.Communication Sciences and Disorder
Dirac-Schr\"odinger equation for quark-antiquark bound states and derivation of its interaction kerne
The four-dimensional Dirac-Schr\"odinger equation satisfied by
quark-antiquark bound states is derived from Quantum Chromodynamics. Different
from the Bethe-Salpeter equation, the equation derived is a kind of first-order
differential equations of Schr\"odinger-type in the position space. Especially,
the interaction kernel in the equation is given by two different closed
expressions. One expression which contains only a few types of Green's
functions is derived with the aid of the equations of motion satisfied by some
kinds of Green's functions. Another expression which is represented in terms of
the quark, antiquark and gluon propagators and some kinds of proper vertices is
derived by means of the technique of irreducible decomposition of Green's
functions. The kernel derived not only can easily be calculated by the
perturbation method, but also provides a suitable basis for nonperturbative
investigations. Furthermore, it is shown that the four-dimensinal
Dirac-Schr\"odinger equation and its kernel can directly be reduced to rigorous
three-dimensional forms in the equal-time Lorentz frame and the
Dirac-Schr\"odinger equation can be reduced to an equivalent
Pauli-Schr\"odinger equation which is represented in the Pauli spinor space. To
show the applicability of the closed expressions derived and to demonstrate the
equivalence between the two different expressions of the kernel, the t-channel
and s-channel one gluon exchange kernels are chosen as an example to show how
they are derived from the closed expressions. In addition, the connection of
the Dirac-Schr\"odinger equation with the Bethe-Salpeter equation is discussed
Renormalization of the Sigma-Omega model within the framework of U(1) gauge symmetry
It is shown that the Sigma-Omega model which is widely used in the study of
nuclear relativistic many-body problem can exactly be treated as an Abelian
massive gauge field theory. The quantization of this theory can perfectly be
performed by means of the general methods described in the quantum gauge field
theory. Especially, the local U(1) gauge symmetry of the theory leads to a
series of Ward-Takahashi identities satisfied by Green's functions and proper
vertices. These identities form an uniquely correct basis for the
renormalization of the theory. The renormalization is carried out in the
mass-dependent momentum space subtraction scheme and by the renormalization
group approach. With the aid of the renormalization boundary conditions, the
solutions to the renormalization group equations are given in definite
expressions without any ambiguity and renormalized S-matrix elememts are
exactly formulated in forms as given in a series of tree diagrams provided that
the physical parameters are replaced by the running ones. As an illustration of
the renormalization procedure, the one-loop renormalization is concretely
carried out and the results are given in rigorous forms which are suitable in
the whole energy region. The effect of the one-loop renormalization is examined
by the two-nucleon elastic scattering.Comment: 32 pages, 17 figure
Generation of GHZ entangled states of photons in multiple cavities via a superconducting qutrit or an atom through resonant interaction
We propose an efficient method to generate a GHZ entangled state of n photons
in n microwave cavities (or resonators) via resonant interaction to a single
superconducting qutrit. The deployment of a qutrit, instead of a qubit, as the
coupler enables us to use resonant interactions exclusively for all
qutrit-cavity and qutrit-pulse operations. This unique approach significantly
shortens the time of operation which is advantageous to reducing the adverse
effects of qutrit decoherence and cavity decay on fidelity of the protocol.
Furthermore, the protocol involves no measurement on either the state of qutrit
or cavity photons. We also show that the protocol can be generalized to other
systems by replacing the superconducting qutrit coupler with different types of
physical qutrit, such as an atom in the case of cavity QED, to accomplish the
same task.Comment: 11 pages, 5 figures, accepted by Phys. Rev.
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