Axial Anomaly and the Nucleon Spin

In this letter, we have taken a particular Lagrangian, which was introduced to resolve U(1) problem, as an effective QCD Lagrangian, and have derived a formula of the quark content of the nucleon spin. The difference between quark content of the proton (\Delta\Sigma_p) and that of the neutron (\Delta\Sigma_n) is evaluated by this formula. Neglecting the higher-order isospin corrections, this formula can reduce to Efremov's results in the large N_c limit.Comment: (1) A few changes and corrections made following Referee. (2) The difference between quark content of the proton (\Delta\Sigma_p) and that of the neutron (\Delta\Sigma_n) is evaluated. Neglecting the higher-order isospin corrections, this formula can reduce to Efremov's results in the large N_c limi

Prospect of Making Ceramic Shell Mold by Ceramic Laser Fusion

Manufacturing prototypical castings by conventional investment casting not only takes several weeks, but also is prohibitively expensive. Z Corporation in USA, EOS GmbH and IPT in Germany employ the techniques of 3DP and SLS respectively to make directly ceramic shell molds for metal castings. Although those techniques dramatically reduce time expenditure and production cost, each layer cannot be thinner than 50 µm because of using powder to pave layers. The dimensional accuracy and roughness of the castings still cannot meet the specification of precision casting. Therefore, in this paper the ceramic laser fusion (CLF) was used to pave layers. Each layer can be thinner than 25 µm, so that the step effect can be diminished and the workpiece surface can be smoother; drying time will be shortened dramatically. Moreover, the inherent solid-state support formed by green portion has the capability of preventing upward and downward deformation of the scanned cross sections. In order to make shell mold which meets the roughness requirement (Rq=3.048µm) of the precision casting, following issues have to be further studied: (1) design a proper ceramic shell mold structure, (2) design a paving chamber for paving a complete green layer which can be easily collapsed, (3) cut down drying time, (4) optimize laser scanning process parameters with the smallest distortion, (5) eliminate sunken area, (6) reduce layer thickness to less than13µm, (7) control power to guarantee the energy uniformly absorbed by workpiece, and (8) develop a method which can directly clean green portion in cavity from gate.Mechanical Engineerin

Wakes from arrays of buildings

Experiments were carried out in a small wind tunnel in which atmospheric flow around buildings was simulated. Arrays of one, two, three, and four model buildings were tested, and wake profiles of velocity and turbulence were measured. The data indicate the effect of the buildings on the wind environment encountered by aircraft during landing or takeoff operations. It was possible to use the results to locate the boundaries of the air regions affected by the obstacles and to recommend preferred arrangements of buildings to maximize light safety

Multiband effects on the conductivity for a multiband Hubbard model

The newly discovered iron-based superconductors have attracted lots of interests, and the corresponding theoretical studies suggest that the system should have six bands. In this paper, we study the multiband effects on the conductivity based on the exact solutions of one-dimensional two-band Hubbard model. We find that the orbital degree of freedom might enhance the critical value $U_c$ of on-site interaction of the transition from a metal to an insulator. This observation is helpful to understand why undoped High-$T_c$ superconductors are usually insulators, while recently discovered iron-based superconductors are metal. Our results imply that the orbital degree of freedom in the latter cases might play an essential role.Comment: 4 pages, 5 figure

Production and Decay of the Ge73-m Metastable State in a Low-Background Germanium Detector

The $\ge73m$ metastable states decay with a very characteristic signature which allow them to be tagged event-by-event. Studies were performed using data taken with a high-purity germanium detector in a low-background laboratory near a nuclear power reactor core where \nuebar-flux was $\rm{6.4 \times 10^{12} ~ cm^{-2} s^{-1}}$. The measured average and equilibrium production rates of $\ge73m$ were $\rm{(8.7 \pm 0.4)}$ and $\rm{(6.7 \pm 0.3) ~ kg^{-1} day^{-1}}$, respectively. The production channels were studied and identified. By studying the difference in the production of $\ge73m$ between the reactor ON and OFF spectra, the limiting sensitivities at the range of $\rm{\sim 10^{-42} - 10^{-43} ~ cm^2}$ for the cross-sections of neutrino-induced nuclear transitions were derived. The dominant background are due to $\beta$-decays of cosmic-ray induced $^{73}$Ga. The prospects of enhancing the sensitivities at underground locations are discussed.Comment: 16 pages, 10 figure