The influence of oxidative-thermal degradation of polypropylene on measured interface strength of glass fibre-polypropylene

It was previously found that thermal-oxidative degradation of the polypropylene could significantly affect the measured interfacial strength of glass fibre reinforced polypropylene (GF-PP) micro-composite. In this work, different approaches have been employed to justify this influence. Hot-stage microscopy was used to establish a degradation profile of PP microdroplets that had different initial dimensions and results revealed that the reduction in droplet dimensions was affected by not only its initial droplet size and but also the presence of the fibre in the droplet. The Young's moduli of PP microdroplets with different heat treatments were examined by using nanoindentation technique and the results showed that there was significant stiffness deterioration in degraded samples and the severity is also related to the droplet size for a given heat treatment. Comparison of adhesion for GF-PP was also made between degraded and non-degraded samples. It shows that non-degraded samples give much higher values for interface strength of GF-PP than degraded ones

Sensitivity of deexcitation energies of superdeformed secondary minima to the density dependence of symmetry energy with the relativistic mean-field theory

The relationship between deexcitation energies of superdeformed secondary minima relative to ground states and the density dependence of the symmetry energy is investigated for heavy nuclei using the relativistic mean field (RMF) model. It is shown that the deexcitation energies of superdeformed secondary minima are sensitive to differences in the symmetry energy that are mimicked by the isoscalar-isovector coupling included in the model. With deliberate investigations on a few Hg isotopes that have data of deexcitation energies, we find that the description for the deexcitation energies can be improved due to the softening of the symmetry energy. Further, we have investigated deexcitation energies of odd-odd heavy nuclei that are nearly independent of pairing correlations, and have discussed the possible extraction of the constraint on the density dependence of the symmetry energy with the measurement of deexcitation energies of these nuclei.Comment: 14 pages, 3 figure

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

Time-Dependent Partition-Free Approach in Resonant Tunneling Systems

An extended Keldysh formalism, well suited to properly take into account the initial correlations, is used in order to deal with the time-dependent current response of a resonant tunneling system. We use a \textit{partition-free} approach by Cini in which the whole system is in equilibrium before an external bias is switched on. No fictitious partitions are used. Besides the steady-state responses one can also calculate physical dynamical responses. In the noninteracting case we clarify under what circumstances a steady-state current develops and compare our result with the one obtained in the partitioned scheme. We prove a Theorem of asymptotic Equivalence between the two schemes for arbitrary time-dependent disturbances. We also show that the steady-state current is independent of the history of the external perturbation (Memory Loss Theorem). In the so called wide-band limit an analytic result for the time-dependent current is obtained. In the interacting case we propose an exact non-equilibrium Green function approach based on Time Dependent Density Functional Theory. The equations are no more difficult than an ordinary Mean Field treatment. We show how the scattering-state scheme by Lang follows from our formulation. An exact formula for the steady-state current of an arbitrary interacting resonant tunneling system is obtained. As an example the time-dependent current response is calculated in the Random Phase Approximation.Comment: final version, 18 pages, 9 figure

Protons in near earth orbit

The proton spectrum in the kinetic energy range 0.1 to 200 GeV was measured by the Alpha Magnetic Spectrometer (AMS) during space shuttle flight STS-91 at an altitude of 380 km. Above the geomagnetic cutoff the observed spectrum is parameterized by a power law. Below the geomagnetic cutoff a substantial second spectrum was observed concentrated at equatorial latitudes with a flux ~ 70 m^-2 sec^-1 sr^-1. Most of these second spectrum protons follow a complicated trajectory and originate from a restricted geographic region.Comment: 19 pages, Latex, 7 .eps figure

Search for antihelium in cosmic rays

The Alpha Magnetic Spectrometer (AMS) was flown on the space shuttle Discovery during flight STS-91 in a 51.7 degree orbit at altitudes between 320 and 390 km. A total of 2.86 * 10^6 helium nuclei were observed in the rigidity range 1 to 140 GV. No antihelium nuclei were detected at any rigidity. An upper limit on the flux ratio of antihelium to helium of < 1.1 * 10^-6 is obtained.Comment: 18 pages, Latex, 9 .eps figure

A Study of Cosmic Ray Secondaries Induced by the Mir Space Station Using AMS-01

The Alpha Magnetic Spectrometer (AMS-02) is a high energy particle physics experiment that will study cosmic rays in the $\sim 100 \mathrm{MeV}$ to $1 \mathrm{TeV}$ range and will be installed on the International Space Station (ISS) for at least 3 years. A first version of AMS-02, AMS-01, flew aboard the space shuttle \emph{Discovery} from June 2 to June 12, 1998, and collected $10^8$ cosmic ray triggers. Part of the \emph{Mir} space station was within the AMS-01 field of view during the four day \emph{Mir} docking phase of this flight. We have reconstructed an image of this part of the \emph{Mir} space station using secondary $\pi^-$ and $\mu^-$ emissions from primary cosmic rays interacting with \emph{Mir}. This is the first time this reconstruction was performed in AMS-01, and it is important for understanding potential backgrounds during the 3 year AMS-02 mission.Comment: To be submitted to NIM B Added material requested by referee. Minor stylistic and grammer change

Cosmic-ray positron fraction measurement from 1 to 30 GeV with AMS-01

A measurement of the cosmic ray positron fraction e+/(e+ + e-) in the energy range of 1-30 GeV is presented. The measurement is based on data taken by the AMS-01 experiment during its 10 day Space Shuttle flight in June 1998. A proton background suppression on the order of 10^6 is reached by identifying converted bremsstrahlung photons emitted from positrons