2,016 research outputs found
Analysis on dynamic tensile extrusion behavior of UFG OFHC Cu
Dynamic tensile extrusion (DTE) tests with the strain rate order of similar to 10(5) s(-1) were conducted on coarse grained (CG) Cu and ultrafine grained (UFG) Cu. ECAP of 16 passes with route B-c was employed to fabricate UFG Cu. DTE tests were carried out by launching the sphere samples to the conical extrusion die at a speed of similar to 475 m/sec in a vacuumed gas gun system. UFG Cu was fragmented into 3 pieces and showed a DTE elongation of similar to 340%. CG Cu exhibited a larger DTE elongation of similar to 490% with fragmentation of 4 pieces. During DTE tests, dynamic recrystallization occurred in UFG Cu, but not in CG Cu. In order to examine the DTE behavior of CG Cu and UFG Cu under very high strain rates, a numerical analysis was undertaken by using a commercial finite element code (LS-DYNA 2D axis-symmetric model) with the Johnson - Cook model. The numerical analysis correctly predicted fragmentation and DTE elongation of CG Cu. But, the experimental DTE elongation of UFG Cu was much smaller than that predicted by the numerical analysis. This difference is discussed in terms of microstructural evolution of UFG Cu during DTE tests.111Ysciescopu
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Mo-La2O3 multilayer metallization systems for high temperature surface acoustic wave sensor devices
Developing advanced thin film materials is the key challenge in high-temperature applications of surface acoustic wave sensor devices. One hundred nanometer thick (Mo-La2O3) multilayer systems were fabricated at room temperature on thermally oxidized (100) Si substrates (SiO2/Si) to study the effect of lanthanum oxide on the electrical resistivity of molybdenum thin films and their high-temperature stability. The multilayer systems were deposited by the magnetron sputter deposition of extremely thin (≤1 nm) La interlayers in between adjacent Mo layers. After deposition of each La layer the process was interrupted for 25 to 60 min to oxidize the La using the residual oxygen in the high vacuum of the deposition chamber. The samples were annealed at 800 °C in high vacuum for up to 120 h. In case of a 1 nm thick La interlayer in-between the Mo a continuous layer of La2O3 is formed. For thinner La layers an interlayer between adjacent Mo layers is observed consisting of a (La2O3-Mo) mixed structure of molybdenum and nm-sized lanthanum oxide particles. Measurements show that the (Mo-La2O3) multilayer systems on SiO2/Si substrates are stable at least up to 800 °C for 120 h in high vacuum conditions
Time and Amplitude of Afterpulse Measured with a Large Size Photomultiplier Tube
We have studied the afterpulse of a hemispherical photomultiplier tube for an
upcoming reactor neutrino experiment. The timing, the amplitude, and the rate
of the afterpulse for a 10 inch photomultiplier tube were measured with a 400
MHz FADC up to 16 \ms time window after the initial signal generated by an LED
light pulse. The time and amplitude correlation of the afterpulse shows several
distinctive groups. We describe the dependencies of the afterpulse on the
applied high voltage and the amplitude of the main light pulse. The present
data could shed light upon the general mechanism of the afterpulse.Comment: 11 figure
A Neutron Elastic Diffuse Scattering Study of PMN
We have performed elastic diffuse neutron scattering studies on the relaxor
Pb(MgNb)O (PMN). The measured intensity distribution near a
(100) Bragg peak in the (hk0) scattering plane assumes the shape of a butterfly
with extended intensity in the (110) and (10) directions. The
temperature dependence of the diffuse scattering shows that both the size of
the polar nanoregions (PNR) and the integrated diffuse intensity increase with
cooling even for temperatures below the Curie temperature K.Comment: Submitted to PR
Quantum Stability of Accelerated Black Holes
We study quantum aspects of the accelerated black holes in some detail.
Explicitly shown is the fact that a uniform acceleration stabilizes certain
charged black holes against the well-known thermal evaporation. Furthermore, a
close inspection of the geometry reveals that this is possible only for
near-extremal black holes and that most nonextremal varieties continue to
evaporate with a modified spectrum under the acceleration. We also introduce a
two-dimensional toy model where the energy-momentum flow is easily obtained for
general accelerations, and find the behavior to be in accordance with the
four-dimensional results. After a brief comparison to the classical system of a
uniformly accelerated charge, we close by pointing out the importance of this
result in the WKB expansion of the black hole pair-creation rate.Comment: LaTeX, 22 pages, 5 uuencoded figures (minor errors corrected, more
discussions on the case with black holes formed by gravitational collapse.
Analysis of air-water two phase natural circulation flow by using RELAP5/MOD3
Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Air-water two phase natural circulation flow in the T-HERMES (Thermo-Hydraulic Evaluation of Reactor cooling Mechanism by External Self-induced flow)-1D experiment has been verified and evaluated by RELAP5/MOD3 computer code. The RELAP5 results have shown that an increase in the coolant inlet area leads to an increase in the water circulation mass flow rate. However, the water outlet area has no influence on the water circulation mass flow rate. As the coolant outlet moves to a lower position, the water circulation mass flow rate decreases. The water level has no influence on the water circulation mass flow rate
Z boson pair production at LHC in a stabilized Randall-Sundrum scenario
We study the Z boson pair production at LHC in the Randall-Sundrum scenario
with the Goldberger-Wise stabilization mechanism. It is shown that
comprehensive account of the Kaluza-Klein graviton and radion effects is
crucial to probe the model: The KK graviton effects enhance the cross section
of on the whole so that the resonance peak of the radion becomes
easy to detect, whereas the RS effects on the process are
rather insignificant. The and invariant-mass distributions are presented
to study the dependence of the RS model parameters. The production of
longitudinally polarized Z bosons, to which the SM contributions are
suppressed, is mainly due to KK gravitons and the radion, providing one of the
most robust methods to signal the RS effects. The sensitivity bounds
on with are also obtained such that
the effective weak scale of order 5 TeV can be experimentally
probed.Comment: 28 pages, LaTex file, 18 eps figure
Magnetically Frustrated Behavior In Multiferroics R Mn2 O 5 (r=bi, Eu, And Dy): A Raman Scattering Study
A temperature dependent Raman scattering study in multiferroic single crystals R Mn2 O5 (R=Bi, Eu, and Dy) was performed. The Raman spectra were measured in the range from 150 to 450 cm-1 involving mostly Mn-O-Mn bending vibrations, complementing our previous work in a higher frequency range involving Mn-O stretching modes. A number of studied phonons present anomalous frequency behavior below a characteristic temperature, T* ∼60-65 K, such as that found for the stretching modes. The sign and magnitude of such anomalous behavior appear to be correlated with the ionic radius of R, being softening for R=Bi and hardening for R=Eu and Dy in the range between TC TN and T*. The anomalous phonon behaviors in both bending and stretching modes are consistent with an interpretation in terms of the spin-phonon coupling in a scenario of strong magnetic correlations. © 2007 American Institute of Physics.1019Wang, J., (2003) Science, 299, p. 1719Hur, N., Park, S., Sharma, P.A., Ahn, J.S., Guha, S., Cheong, S.-W., (2004) Nature (London), 429, p. 392Alonso, J.A., Casais, M.T., Martínez-Lope, M.J., Martínez, J.L., Fernández-Díaz, M.T., (1997) J. Phys.: Condens. Matter, 9, p. 8515Kagomiya, I., Kohn, K., Uchiyama, T., (2002) Ferroelectrics, 280, p. 297Hur, N., Park, S., Sharma, P.A., Guha, S., Cheong, S.-W., (2004) Phys. Rev. Lett., 93, p. 107207Muoz, A., Alonso, J.A., Casais, M.T., Martínez-Lope, M.J., Martínez, J.L., Fernández-Díaz, M.T., (2002) Phys. Rev. B, 65, p. 144423Golovenchits, E.I., Sanina, V.A., Babinskii, A.V., (1997) JETP, 85, p. 156Chapon, L.C., Blake, G.R., Gutmann, M.J., Park, S., Hur, N., Radaelli, P.G., Cheong, S.-W., (2004) Phys. Rev. Lett., 93, p. 177402Blake, G.P., Chapon, L.C., Radaelli, P.G., Park, S., Hur, N., Cheong, S.-W., Rodríguez-Carvajal, J., (2005) Phys. Rev. B, 71, p. 214402Polyakov, V., Plakhty, V., Bonnet, M., Burlet, P., Regnault, L.-P., Gavrilov, S., Zobkalo, I., Smirnov, O., (2001) Physica B, 297, p. 208Higashiyama, D., Miyasaka, S., Kida, N., Arima, T., Tokura, Y., (2004) Phys. Rev. B, 70, p. 174405Ramirez, A.P., (2001) Handbook of Magnetic Materials, 13, pp. 423-520. , Elsevier, New YorkGarcía-Flores, A.F., (2006) Phys. Rev. B, 73, p. 104411Baltensperger, W., Helman, J.S., (1968) Helv. Phys. Acta, 41, p. 668Granado, E., (2001) Phys. Rev. Lett., 86, p. 5385Sushkov, A.B., Tchernyshyov, O., Ratcliff, I.I.W., Cheong, S.-W., Drew, H.D., (2004) Phys. Rev. Lett., 94, p. 13720
BCS theory for s+g-wave superconductivity borocarbides Y(Lu)NiBC
The s+g mixed gap function \Delta_k=\Delta {[(1-x)-x\sin^4\theta\cos4\phi]}
(x: weight of g-wave component) has been studied within BCS theory. By suitable
consideration of the pairing interaction, we have confirmed that the
coexistence of s- and g-wave, as well as the state with equal s and g
amplitudes (i.e., x=1/2) may be stable. This provides the semi-phenomenological
theory for the s+g-wave superconductivity with point nodes which has been
observed experimentally in borocarbides YNi_2B_2C and possibly in LuNi_2B_2C.Comment: 5 pages, 3 figure
Electronic Structure and Optical Properties of the Co-doped Anatase TiO Studied from First Principles
The Co-doped anatase TiO, a recently discovered room-temperature
ferromagnetic insulator, has been studied by the first-principles calculations
in the pseudo-potential plane-wave formalism within the local-spin-density
approximation (LSDA), supplemented by the full-potential linear augmented plane
wave (FP-LAPW) method. Emphasis is placed on the dependence of its electronic
structures and linear optical properties on the Co-doping concentration and
oxygen vacancy in the system in order to pursue the origin of its
ferromagnetism. In the case of substitutional doping of Co for Ti, our
calculated results are well consistent with the experimental data, showing that
Co is in its low spin state. Also, it is shown that the oxygen vacancy enhances
the ferromagnetism and has larger effect on both the electronic structure and
optical properties than the Co-doping concentration only.Comment: 12 pages, 4 figure
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