1,520 research outputs found
The cyclic stress-strain behavior of PWA 1480 at 650 deg C
The monotonic plastic flow behavior of several single crystal nickel-base, superalloys has been shown to vary significantly with crystallographic orientation. In the present study, the cyclic plastic flow response of one such alloy, PWA 1480, was examined at 650 deg C in air. Single crystal specimens aligned near several crystallographic directions were tested in fully reversed, total-strain-controlled low cycle fatigue tests at a frequency of 0.1 Hz. The cyclic stress-strain response and general cyclic hardening behavior was analyzed as a function of crystallographic orientation and inelastic strain range
Nonclassical Moments and their Measurement
Practically applicable criteria for the nonclassicality of quantum states are
formulated in terms of different types of moments. For this purpose the moments
of the creation and annihilation operators, of two quadratures, and of a
quadrature and the photon number operator turn out to be useful. It is shown
that all the required moments can be determined by homodyne correlation
measurements. An example of a nonclassical effect that is easily characterized
by our methods is amplitude-squared squeezing.Comment: 12 pages, 6 figure
Characterization of quantum angular-momentum fluctuations via principal components
We elaborate an approach to quantum fluctuations of angular momentum based on
the diagonalization of the covariance matrix in two versions: real symmetric
and complex Hermitian. At difference with previous approaches this is SU(2)
invariant and avoids any difficulty caused by nontrivial commutators.
Meaningful uncertainty relations are derived which are nontrivial even for
vanishing mean angular momentum. We apply this approach to some relevant
states.Comment: 10 pages, Two column. New section II and some clarifying comment
Measuring the Density Matrix by Local Addressing
We introduce a procedure to measure the density matrix of a material system.
The density matrix is addressed locally in this scheme by applying a sequence
of delayed light pulses. The procedure is based on the stimulated Raman
adiabatic passage (STIRAP) technique. It is shown that a series of population
measurements on the target state of the population transfer process yields
unambiguous information about the populations and coherences of the addressed
states, which therefore can be determined.Comment: 4 pages, 1 figur
Cavity-assisted spontaneous emission as a single-photon source: Pulse shape and efficiency of one-photon Fock state preparation
Within the framework of exact quantum electrodynamics in dispersing and
absorbing media, we have studied the quantum state of the radiation emitted
from an initially in the upper state prepared two-level atom in a high-
cavity, including the regime where the emitted photon belongs to a wave packet
that simultaneously covers the areas inside and outside the cavity. For both
continuing atom--field interaction and short-term atom--field interaction, we
have determined the spatio-temporal shape of the excited outgoing wave packet
and calculated the efficiency of the wave packet to carry a one-photon Fock
state. Furthermore, we have made contact with quantum noise theories where the
intracavity field and the field outside the cavity are regarded as
approximately representing independent degrees of freedom such that two
separate Hilbert spaces can be introduced.Comment: 16 pages, 7 eps figures; improved version as submitted to Phys. Rev.
Universal measurement of quantum correlations of radiation
A measurement technique is proposed which, in principle, allows one to
observe the general space-time correlation properties of a quantized radiation
field. Our method, called balanced homodyne correlation measurement, unifies
the advantages of balanced homodyne detection with those of homodyne
correlation measurements.Comment: 4 pages, 4 figures, small misprints were corrected, accepted to Phys.
Rev. Let
Patchy Reconnection in a Y-Type Current Sheet
We study the evolution of the magnetic field in a Y-type current sheet
subject to a brief, localized magnetic reconnection event. The reconnection
produces up- and down-flowing reconnected flux tubes which rapidly decelerate
when they hit the Y-lines and underlying magnetic arcade loops at the ends of
the current sheet. This localized reconnection outflow followed by a rapid
deceleration reproduces the observed behavior of post-CME downflowing coronal
voids. These simulations support the hypothesis that these observed coronal
downflows are the retraction of magnetic fields reconnected in localized
patches in the high corona.Comment: 4 pages, 3 figure
Probing the Effect of Cadence on the Estimates of Photospheric Energy and Helicity Injections in Eruptive Active Region NOAA AR 11158
We study how the input-data cadence affects the photospheric energy and helicity injection estimates in eruptive NOAA Active Region 11158. We sample the novel 2.25-minute vector magnetogram and Dopplergram data from the Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) spacecraft to create input datasets of variable cadences ranging from 2.25 minutes to 24 hours. We employ state-of-the-art data processing, velocity, and electric-field inversion methods for deriving estimates of the energy and helicity injections from these datasets. We find that the electric-field inversion methods that reproduce the observed magnetic-field evolution through the use of Faraday's law are more stable against variable cadence: the PDFI (PTD-Doppler-FLCT-Ideal, where PTD refers to Poloidal-Toroidal Decomposition, and FLCT to Fourier Local Correlation Tracking) electric-field inversion method produces consistent injection estimates for cadences from 2.25 minutes up to two hours, implying that the photospheric processes acting on time scales below two hours contribute little to the injections, or that they are below the sensitivity of the input data and the PDFI method. On other hand, the electric-field estimate derived from the output of DAVE4VM (Differential Affine Velocity Estimator for Vector Magnetograms), which does not fulfill Faraday's law exactly, produces significant variations in the energy and helicity injection estimates in the 2.25 minutes - two hours cadence range. We also present a third, novel DAVE4VM-based electric-field estimate, which corrects the poor inductivity of the raw DAVE4VM estimate. This method is less sensitive to the changes of cadence, but it still faces significant issues for the lowest of considered cadences (two hours). We find several potential problems in both PDFI- and DAVE4VM-based injection estimates and conclude that the quality of both should be surveyed further in controlled environments.Peer reviewe
Dual-grating dielectric accelerators driven by a pulse-front-tilted laser
Dielectric laser-driven accelerators (DLAs) can provide high accelerating gradients in the GV/m range due to their higher breakdown thresholds than metals, which opens the way to miniaturize our next-generation particle accelerator facility. However, the electron energy gain is limited by the short interaction length between the laser pulses and the electron bunch for previously reported DLAs. This paper numerically investigates the dual-grating DLAs driven by a pulse-front-tilted (PFT) laser which extends the interaction length and boosts the electrons energy gain. The optical system to generate the PFT laser beam is also studied in detail. By two-dimensional (2D) particle-in-cell simulations we show that such a PFT laser effectively increases the energy gain by more than 100% as compared to that of a normally incident laser beam
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