The Approach of Complex Insert Packaging Fabrication in Stereolithography

The approach of complex insert packaging fabrication in stereolithography is studied in the paper. There are many difficulties being overcome, such as the dispensing shadowing problem caused by the geometric shape of insert, the polymer feeding problem caused by greater insert height than the layer thickness, and the positioning problem of insert that leads to instability of packaging. These drawbacks led to unsatisfactory results of the insert packaging in stereolithography. In order to solve the problems, a new method of complex inserts packaging fabrication in stereolithography is proposed in this paper. Based on the geometric information, function and assembly direction of the inserts, the packaging approach is developed. The approach proposed in this paper has been verified by experiments. It brings considerable contributions to the application of insert packaging in stereolithography. It is also favorable to the improvement of insert packaging efficiency and assembly fabricationMechanical Engineerin

A note on Neuberger's double pass algorithm

We analyze Neuberger's double pass algorithm for the matrix-vector multiplication R(H).Y (where R(H) is (n-1,n)-th degree rational polynomial of positive definite operator H), and show that the number of floating point operations is independent of the degree n, provided that the number of sites is much larger than the number of iterations in the conjugate gradient. This implies that the matrix-vector product $(H)^{-1/2} Y \simeq R^{(n-1,n)}(H) \cdot Y$ can be approximated to very high precision with sufficiently large n, without noticeably extra costs. Further, we show that there exists a threshold $n_T$ such that the double pass is faster than the single pass for $n > n_T$, where $n_T \simeq 12 - 25$ for most platforms.Comment: 18 pages, v3: CPU time formulas are obtained, to appear in Physical Review

The Characteristics and Applications of Ceramic Laser Fusion and Ceramic Laser Sintering

The aim of present study is to investigate the possible application of the ceramic parts which are fabricated with the process of Ceramic Laser Fusion or Ceramic Laser Sintering. The experimental results reveal: (1) CLF can lead to a reduction in the porosity of the ceramic part but also can induce micro-cracks. Therefore, this process cannot produce a part with the required strength by a post-process of infiltration; (2) CLS is capable of fabricating a ceramic part with high porosity. By adjusting the slurry formulation and varying the scanning energy, the open porosity can be over 90vol% of the total porosity. After a post-process of infiltration, the density can be increased to 95%; therefore, CLS can apply to produce a part with high strength. Because the high open porosity leads to a good permeability, the process of CLS is suitable for the fabrication of ceramic shell mold.Mechanical Engineerin

Semimetalic graphene in a modulated electric potential

The $\pi$-electronic structure of graphene in the presence of a modulated electric potential is investigated by the tight-binding model. The low-energy electronic properties are strongly affected by the period and field strength. Such a field could modify the energy dispersions, destroy state degeneracy, and induce band-edge states. It should be noted that a modulated electric potential could make semiconducting graphene semimetallic, and that the onset period of such a transition relies on the field strength. There exist infinite Fermi-momentum states in sharply contrast with two crossing points (Dirac points) for graphene without external fields. The finite density of states (DOS) at the Fermi level means that there are free carriers, and, at the same time, the low DOS spectrum exhibits many prominent peaks, mainly owing to the band-edge states.Comment: 12pages, 5 figure

TeV scale Dark Matter and electroweak radiative corrections

Recent anomalies in cosmic rays data, namely from the PAMELA collaboration, can be interpreted in terms of TeV scale decaying/annihilating Dark Matter. We analyze the impact of radiative corrections coming from the electroweak sector of the Standard Model on the spectrum of the final products at the interaction point. As an example, we consider virtual one loop corrections and real gauge bosons emission in the case of a very heavy vector boson annihilating into fermions. We show that the effect of electroweak corrections is relevant, but not as big as sometimes claimed in the literature. At such high scales, one loop electroweak effects are so big that eventually higher orders/resummations have to be considered: we advocate for the inclusion of these effects in parton shower Montecarlos aiming at the description of TeV scale physics.Comment: Comments added, published versio

On computations of the integrated space shuttle flowfield using overset grids

Numerical simulations using the thin-layer Navier-Stokes equations and chimera (overset) grid approach were carried out for flows around the integrated space shuttle vehicle over a range of Mach numbers. Body-conforming grids were used for all the component grids. Testcases include a three-component overset grid - the external tank (ET), the solid rocket booster (SRB) and the orbiter (ORB), and a five-component overset grid - the ET, SRB, ORB, forward and aft attach hardware, configurations. The results were compared with the wind tunnel and flight data. In addition, a Poisson solution procedure (a special case of the vorticity-velocity formulation) using primitive variables was developed to solve three-dimensional, irrotational, inviscid flows for single as well as overset grids. The solutions were validated by comparisons with other analytical or numerical solution, and/or experimental results for various geometries. The Poisson solution was also used as an initial guess for the thin-layer Navier-Stokes solution procedure to improve the efficiency of the numerical flow simulations. It was found that this approach resulted in roughly a 30 percent CPU time savings as compared with the procedure solving the thin-layer Navier-Stokes equations from a uniform free stream flowfield

CUSHIONING OF THE RUNNING SHOES AFTER LONG-TERM USE

The purpose of this study was to investigate the cushioning properties of the running shoes after long running distance. Each of five subjects wore a new Nike air-shox shoe at the beginning and then at least ran thirty minutes on the same treadmill once or twice a week. The results of material test showed that impact force peaks significantly increased as the running distance increased. However, in the subject test, the tibial peak accelerations decreased as the running distance increased. It seemed to indicate that the subjects accommodate themselves to the material characteristics of the testing shoe by reducing the impact energies as heel strike. Based on the results, the cushioning abilities of the running shoes were attenuated after 300 km running distance. In the future, the change of the cushioning abilities of the running shoes should be monitored after more running distances