Impression Creep Behavior of Sn-3.5Ag-0.7Cu/Cu Brazed

AbstractBrazing, as one of the major connection technology, has been widely used in different areas such as aviation, aerospace, electronics and chemical industries etc. Sometimes creep fracture can be found in the brazed joints when they are used at high temperature. The conventional characterized method for creep properties cannot be used to study the brazed joints due to their small size. The impression technology has the potential to be used to study the creep properties of brazed joints, since no special requirements are needed for the size and shape of to-be-measured materials. In this investigation, Sn-3.5Ag-0.7Cu/Cu brazed joint is created and its creep properties is measured by impression creep testing. The effect of punching stress and temperature is studied on the impressing depth, which change from 70 to 100MPa and 80-130 oC, respectively. The microstructure of Sn-3.5Ag-0.7Cu/Cu is examined by Optical Microscope (OM), Scanning Electron Microscope (SEM) and Energy Dispersive Spectra (EDS). The results show that the impressing creep depth increases with the rise of temperature and punching stress. Creep resistance of the diffusion region has obvious effect on the creep resistance of the weld. The experimental results can provide the basis for the structural integrity analysis of brazed joints

On quantization of weakly nonlinear lattices. Envelope solitons

A way of quantizing weakly nonlinear lattices is proposed. It is based on introducing "pseudo-field" operators. In the new formalism quantum envelope solitons together with phonons are regarded as elementary quasi-particles making up boson gas. In the classical limit the excitations corresponding to frequencies above linear cut-off frequency are reduced to conventional envelope solitons. The approach allows one to identify the quantum soliton which is localized in space and understand existence of a narrow soliton frequency band.Comment: 5 pages. Phys. Rev. E (to appear

Subplate in a rat model of preterm hypoxia-ischemia.

OBJECTIVE: Hypoxia-ischemia (HI) in preterm infants primarily leads to injuries in the cerebral white matter. However, there is growing evidence that perinatal injury in preterms can also involve other zones including the cortical gray matter. In a neonatal rat model of HI, selective vulnerability of subplate has been suggested using BrdU birth-dating methods. In this study, we aimed to investigate the neuropathological changes of the subplate and deep layers of the cortex following cerebral HI in neonatal rats with specific cell markers. METHODS: P2 rats underwent permanent occlusion of the right common carotid artery followed by a period of hypoxia. P8 rats were analyzed using immunohistochemistry; subplate and deep layers cells were quantified and compared with sham-operated case. RESULTS: A large variability in the extent of the cerebral injury was apparent. For the three analyzed subplate populations (Nurr1+, Cplx3+, and Ctgf+ cells), no significant cell reduction was observed in mild and moderate cases. Only in severe cases, subplate cells were strongly affected, but these injuries were always accompanied by the cell reductions in layers VI and V. INTERPRETATION: We could therefore not confirm a specific vulnerability of subplate cells compared to other deep layers or the white matter in our model

Structural Strength and Service Life of the Extrusion Forming Die for Agricultural Engine Piston Heads

Three-tier high-strength prestressed combination concave dies are designed to manifacture highpower corn combine harvester engine piston heads. This design integrates the advantages of traditional casting or hot die forging and warm extrusion. The following key parameters, viz radial dimensions of each mating layer, axial bonding and radial contact interaction, are obtained by theoretical calculation. Nonlinear analysis of the contact interaction was carried out, and the die contact condition was studied at no-load and full-load. Based on the Archard wear theory, thermomechanical bonding was studied in operation of the die. Through numerical simulation of the die wear in each operation cycle, the univariate linear regression equation of the die service life was derived, and the reliability of this equation was verified. The results show that the die contact is both stable and reliable if the radial contact interaction of the inner and outer layers is δ₂= 1.9716 mm and δ₃= 1.3870 mm, respectively. With the nitriding layer thickness of 0.24 mm, the extrusion die service life in the production of piston heads corresponds to 6357 pieces.Разработаны трехъярусные высокопрочные предварительно-напряженные многоместные вогнутые головки для изготовления днищ поршня двигателя мощного кукурузоуборочного комбайна. Конструкция соединяет в себе преимущества литья или горячей ковки и горячей экструзии. Радиальные размеры каждого соединяемого слоя, осевое сцепление и радиальное контактное взаимодействие рассчитаны теоретически. Выполнен нелинейный анализ контактного взаимодействия, изучены условия контактирования в головке при нулевой и полной нагрузке. На основании теории износа Арчарда выполнена оценка термомеханического сцепления в процессе эксплуатации головки. Путем численного моделирования износа головки в каждом рабочем цикле получено однопараметрическое уравнение линейной регрессии для срока ее службы; проверена достоверность данного уравнения. Показано, что контакт в головке устойчив и надежен, при радиальном контактном взаимодействии внутреннего и наружного слоев δ₂= 1.9716 мм и δ₃= 1.3870 мм соответственно. При толщине нитридного слоя 0,24 мм срок службы экструзионной головки в производстве днищ поршня соответствует 6357 изделиям

Quantum lattice dynamical effects on the single-particle excitations in 1D Mott and Peierls insulators

As a generic model describing quasi-one-dimensional Mott and Peierls insulators, we investigate the Holstein-Hubbard model for half-filled bands using numerical techniques. Combining Lanczos diagonalization with Chebyshev moment expansion we calculate exactly the photoemission and inverse photoemission spectra and use these to establish the phase diagram of the model. While polaronic features emerge only at strong electron-phonon couplings, pronounced phonon signatures, such as multi-quanta band states, can be found in the Mott insulating regime as well. In order to corroborate the Mott to Peierls transition scenario, we determine the spin and charge excitation gaps by a finite-size scaling analysis based on density-matrix renormalization group calculations.Comment: 5 pages, 5 figure

Tunneling of quantum rotobreathers

We analyze the quantum properties of a system consisting of two nonlinearly coupled pendula. This non-integrable system exhibits two different symmetries: a permutational symmetry (permutation of the pendula) and another one related to the reversal of the total momentum of the system. Each of these symmetries is responsible for the existence of two kinds of quasi-degenerated states. At sufficiently high energy, pairs of symmetry-related states glue together to form quadruplets. We show that, starting from the anti-continuous limit, particular quadruplets allow us to construct quantum states whose properties are very similar to those of classical rotobreathers. By diagonalizing numerically the quantum Hamiltonian, we investigate their properties and show that such states are able to store the main part of the total energy on one of the pendula. Contrary to the classical situation, the coupling between pendula necessarily introduces a periodic exchange of energy between them with a frequency which is proportional to the energy splitting between quasi-degenerated states related to the permutation symmetry. This splitting may remain very small as the coupling strength increases and is a decreasing function of the pair energy. The energy may be therefore stored in one pendulum during a time period very long as compared to the inverse of the internal rotobreather frequency.Comment: 20 pages, 11 figures, REVTeX4 styl

Surprises in the Orbital Magnetic Moment and g-Factor of the Dynamic Jahn-Teller Ion C_{60}^-

We calculate the magnetic susceptibility and g-factor of the isolated C_{60}^- ion at zero temperature, with a proper treatment of the dynamical Jahn-Teller effect, and of the associated orbital angular momentum, Ham-reduced gyromagnetic ratio, and molecular spin-orbit coupling. A number of surprises emerge. First, the predicted molecular spin-orbit splitting is two orders of magnitude smaller than in the bare carbon atom, due to the large radius of curvature of the molecule. Second, this reduced spin-orbit splitting is comparable to Zeeman energies, for instance, in X-band EPR at 3.39KGauss, and a field dependence of the g-factor is predicted. Third, the orbital gyromagnetic factor is strongly reduced by vibron coupling, and so therefore are the effective weak-field g-factors of all low-lying states. In particular, the ground-state doublet of C_{60}^- is predicted to show a negative g-factor of \sim -0.1.Comment: 19 pages RevTex, 2 postscript figures include

Controlling laser spectra in a phaseonium photonic crystal using maser

We study the control of quantum resonances in photonic crystals with electromagnetically induced transparency driven by microwave field. In addition to the control laser, the intensity and phase of the maser can alter the transmission and reflection spectra in interesting ways, producing hyperfine resonances through the combined effects of multiple scattering in the superstructure.Comment: 7 pages, 4 figure

Relaxation channels of two-vibron bound states in \alpha-helix proteins

Relaxation channels for two-vibron bound states in an anharmonic alpha-helix protein are studied. It is pointed out that the relaxation originates in the interaction between the dressed anharmonic vibrons and the remaining phonons. This interaction is responsible for the occurrence of transitions between two-vibron eigenstates mediated by both phonon absorption and phonon emission. At biological temperature, it is shown that the relaxation rate does not significantly depends on the nature of the two-vibron state involved in the process. Therefore, the lifetime for both bound and free states is of the same order of magnitude and ranges between 0.1 and 1.0 ps for realistic parameters. By contrast, the relaxation channels strongly depend on the nature of the two-vibron states which is a consequence of the breather-like behavior of the two-vibron bound states.Comment: octobre 2003 - soumis Phys. Rev.