62,324 research outputs found
Exponential sum approximations for
Given and , the function may be approximated
for in a compact interval by a sum of terms of the form
, with parameters and . One such an approximation, studied
by Beylkin and Monz\'on, is obtained by applying the trapezoidal rule to an
integral representation of , after which Prony's method is applied
to reduce the number of terms in the sum with essentially no loss of accuracy.
We review this method, and then describe a similar approach based on an
alternative integral representation. The main difference is that the new
approach achieves much better results before the application of Prony's method;
after applying Prony's method the performance of both is much the same.Comment: 18 pages, 5 figures. I have completely rewritten this paper because
after uploading the previous version I realised that there is a much better
approach. Note the change to the title. Have included minor corrections
following revie
Research on forging forming force in the composite technology of cross wedge rolling (CWR) and forging for universal joint fork
In this paper,the forging process of universal joint fork of automobile transmission shaft is simulated and the change of forming force of die forging is studied on the basis of the blank produced by cross wedge rolling (CWR). Temperature / T , friction factor / c and falling speed of upper die / V are the main process parameters affecting the forging forming force / F of universal joint fork. The effects of temperature, friction factor and speed on the forming force were studied respectively by single factor method. The results show that the lower the temperature, the greater the friction factor, the slower the speed, the greater the forming force, the more difficult for forming. The orthogonal test is designed and it obtained the order of process parameters affecting the forming force of die forging that is T > c > V and the best combination of process that the temperature is 1 100 °C the friction factor is 0,2 and speed of upper die is 150 mm/s
Influence of intrinsic decoherence on nonclassical properties of the output of a Bose-Einstein condensate
We investigate nonclassical properties of the output of a Bose-Einstein
condensate in Milburn's model of intrinsic decoherence. It is shown that the
squeezing property of the atom laser is suppressed due to decoherence.
Nevertheless, if some very special conditions were satisfied, the squeezing
properties of atom laser could be robust against the decoherence.Comment: 17 pages, 5 figures, Late
Reexamining the temperature and neutron density conditions for r-process nucleosynthesis with augmented nuclear mass models
We explore the effects of nuclear masses on the temperature and neutron
density conditions required for r-process nucleosynthesis using four nuclear
mass models augmented by the latest atomic mass evaluation. For each model we
derive the conditions for producing the observed abundance peaks at mass
numbers A ~ 80, 130, and 195 under the waiting-point approximation and further
determine the sets of conditions that can best reproduce the r-process
abundance patterns (r-patterns) inferred for the solar system and observed in
metal-poor stars of the Milky Way halo. In broad agreement with previous
studies, we find that (1) the conditions for producing abundance peaks at A ~
80 and 195 tend to be very different, which suggests that, at least for some
nuclear mass models, these two peaks are not produced simultaneously; (2) the
typical conditions required by the critical waiting-point (CWP) nuclei with the
N = 126 closed neutron shell overlap significantly with those required by the
N=82 CWP nuclei, which enables coproduction of abundance peaks at A ~ 130 and
195 in accordance with observations of many metal-poor stars; and (3) the
typical conditions required by the N = 82 CWP nuclei can reproduce the
r-pattern observed in the metal-poor star HD 122563, which differs greatly from
the solar r-pattern. We also examine how nuclear mass uncertainties affect the
conditions required for the r-process and identify some key nuclei
including76Ni to 78Ni, 82Zn, 131Cd, and 132Cd for precise mass measurements at
rare-isotope beam facilities.Comment: 28 pages,9 figures,1 tabl
Anomalous microwave response of high-temperature superconducting thin-film microstrip resonator in weak dc magnetic fields
We have studied an anomalous microwave (mw) response of superconducting
YBa_{2}Cu_{3}O_{7-delta} (YBCO) microstrip resonators in the presence of a weak
dc magnetic field, H_{dc}. The surface resistance (R_{s}) and reactance (X_{s})
show a correlated non-monotonic behaviour as a function of H_{dc}. R_{s} and
X_{s} were found to initially decrease with elevated H_{dc} and then increase
after H_{dc} reaches a crossover field, H_{c}, which is independent of the
amplitude and frequency of the input mw signal within the measurements. The
frequency dependence of R_{s} is almost linear at fixed H_{dc} with different
magnitudes (H_{c}). The impedance plane analysis
demonstrates that r_{H}, which is defined as the ratio of the change in
R_{s}(H_{dc}) and that in X_{s}(H_{dc}), is about 0.6 at H_{dc}<H_{c} and 0.1
at H_{dc}>H_{c}. The H_{dc} dependence of the surface impedance is
qualitatively independent of the orientation of H_{dc}.Comment: REVTex 3.1, 5 pages, 6 EPS figures, submitted to Physica
Entanglement with phase decoherence
The system of an atom couples to two distinct optical cavities with phase
decoherence is studied by making use of a dynamical algebraic method. We adopt
the concurrence to characterize the entanglement between atom and cavities or
between two optical cavities in the presence of the phase decoherence. It is
found that the entanglement between atom and cavities can be controlled by
adjusting the detuning parameter. Finally, we show that even if the atom is
initially prepared in a maximally mixed state, it can also entangle the two
mode cavity fields.Comment: 9 pages, 6 figures, lete
Finite element simulation of deformation behavior of prefabricated holes in ultra-heavy plates by gradient temperature rolling
Based on the Deform-3D finite element simulation software, the numerical analysis of prefabricated holes in the core of ultra-heavy plates is carried out in different rolling schemes. In this paper, the deformation of the hole in core under uniform temperature rolling (UTR) is compared by different gradient temperature rolling (GTR) processes. The results show that the GTR can improve the core deformation compared with the UTR. The increase of the number of water cooling can accelerate the welding of the core holes and the healing of the final gap, and multi-pass watercooled GTR should be used for ultra-heavy plate rolling
Finite element simulation of deformation behavior of prefabricated holes in ultra-heavy plates by gradient temperature rolling
Based on the Deform-3D finite element simulation software, the numerical analysis of prefabricated holes in the core of ultra-heavy plates is carried out in different rolling schemes. In this paper, the deformation of the hole in core under uniform temperature rolling (UTR) is compared by different gradient temperature rolling (GTR) processes. The results show that the GTR can improve the core deformation compared with the UTR. The increase of the number of water cooling can accelerate the welding of the core holes and the healing of the final gap, and multi-pass watercooled GTR should be used for ultra-heavy plate rolling
Differential flow in heavy-ion collisions at balance energies
A strong differential transverse collective flow is predicted for the first
time to occur in heavy-ion collisions at balance energies. We also give a novel
explanation for the disappearance of the total transverse collective flow at
the balance energies. It is further shown that the differential flow especially
at high transverse momenta is a useful microscope capable of resolving the
balance energy's dual sensitivity to both the nuclear equation of state and
in-medium nucleon-nucleon cross sections in the reaction dynamics.Comment: Phys. Rev. Lett. (1999) in pres
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