4,221 research outputs found
Application of Cryogenic Treatment to Extend the Life of the TiAlN-Coated Tungsten Carbide Milling Cutter
Cutting tools are important to the manufacturing industry since they will affect production efficiency and product quality. Cryogenic treatment can improve the material properties by decreasing residual stress, stabilizing dimensional accuracy, and increasing wear resistance. The purpose of this study is to investigate the feasibility and effect of cryogenic treatment on the performance of TiAlN-coated tungsten carbide milling cutters for machining the Inconel alloy 625 in terms of different testing methods (e.g., hardness, wear resistance, residual stress, microstructure, and tool life test). Experimental results indicate that after cryogenic treatment there is less wear, the microstructure is denser, residual stress is decreased, the adhesion of coating and tungsten carbide is improved, and the tool life is effectively improved
Stability of nonuniform rotor blades in hover using a mixed formulation
A mixed formulation for calculating static equilibrium and stability eigenvalues of nonuniform rotor blades in hover is presented. The static equilibrium equations are nonlinear and are solved by an accurate and efficient collocation method. The linearized perturbation equations are solved by a one step, second order integration scheme. The numerical results correlate very well with published results from a nearly identical stability analysis based on a displacement formulation. Slight differences in the results are traced to terms in the equations that relate moments to derivatives of rotations. With the present ordering scheme, in which terms of the order of squares of rotations are neglected with respect to unity, it is not possible to achieve completely equivalent models based on mixed and displacement formulations. The one step methods reveal that a second order Taylor expansion is necessary to achieve good convergence for nonuniform rotating blades. Numerical results for a hypothetical nonuniform blade, including the nonlinear static equilibrium solution, were obtained with no more effort or computer time than that required for a uniform blade
Self-limited oxide formation in Ni(111) oxidation
The oxidation of the Ni(111) surface is studied experimentally with low
energy electron microscopy and theoretically by calculating the electron
reflectivity for realistic models of the NiO/Ni(111) surface with an ab-initio
scattering theory. Oxygen exposure at 300 K under ultrahigh-vacuum conditions
leads to the formation of a continuous NiO(111)-like film consisting of
nanosized domains. At 750 K, we observe the formation of a nano-heterogeneous
film composed primarily of NiO(111)-like surface oxide nuclei, which exhibit
virtually the same energy-dependent reflectivity as in the case of 300 K and
which are separated by oxygen-free Ni(111) terraces. The scattering theory
explains the observed normal incidence reflectivity R(E) of both the clean and
the oxidized Ni(111) surface. At low energies R(E) of the oxidized surface is
determined by a forbidden gap in the k_parallel=0 projected energy spectrum of
the bulk NiO crystal. However, for both low and high temperature oxidation a
rapid decrease of the reflectivity in approaching zero kinetic energy is
experimentally observed. This feature is shown to characterize the thickness of
the oxide layer, suggesting an average oxide thickness of two NiO layers.Comment: 10 pages (in journal format), 9 figure
Sixty GHz IMPATT diode development
The objective of this program is to develop 60 GHz GaAs IMPATT Diodes suitable for communications applications. The performance goal of the 60 GHz IMPATT is 1W CW output power with a conversion efficiency of 15 percent and 10 year life time. During the course of the program, double drift (DD) GaAs IMPATT Diodes have been developed resulting in the state of the art performance at V band frequencies. A CW output power of 1.12 W was demonstrated at 51.9 GHz with 9.7 percent efficiency. The best conversion efficiency achieved was 15.3 percent. V band DD GaAs IMPATTs were developed using both small signal and large signal analyses. GaAs wafers of DD flat, DD hybrid, and DD Read profiles using molecular beam epitaxy (MBE) were developed with excellent doping profile control. Wafer evaluation was routinely made by the capacitance versus voltage (C-V) measurement. Ion mass spectrometry (SIMS) analysis was also used for more detailed profile evaluation
Activated O2 dissociation and formation of oxide islands on the Be(0001) surface: Another atomistic model for metal oxidation
By simulating the dissociation of O2 molecules on the Be(0001) surface using
the first-principles molecular dynamics approach, we propose a new atomistic
model for the surface oxidation of sp metals. In our model, only the
dissociation of the first oxygen molecule needs to overcome an energy barrier,
while the subsequent oxygen molecules dissociate barrierlessly around the
adsorption area. Consequently, oxide islands form on the metal surface, and
grow up in a lateral way. We also discover that the firstly dissociated oxygen
atoms are not so mobile on the Be(0001) surface, as on the Al(111) surface. Our
atomistic model enlarges the knowledge on metal surface oxidations by perfectly
explaining the initial stage during the surface oxidation of Be, and might be
applicable to some other sp metal surfaces.Comment: 5 pages, 4 figure
Wren’s Walk-Off Bests No. 23 Clemson to Even the Series
Wren’s Walk-Off Bests No. 23 Clemson to Even the Series Junior right fielder hits a bases loaded single with two outs in the nint
Identification of tumor-associated proteins in oral tongue squamous cell carcinoma by proteomics
Oral tongue carcinoma is an aggressive tumor that particularly affects chronic smokers, drinkers and betel squid chewers. Patients often present symptoms at a late stage, and there is a high recurrence rate after treatment. In this article, we report the first proteomic analysis of oral tongue carcinoma to globally search for tumor related proteins. Apart from helping us to understand the molecular pathogenesis of the carcinoma, these proteins may also have potential clinical applications as biomarkers, enabling the tumor to be identified at an early stage in high risk individuals, treatment response to be predicted, and residual or recurrent carcinoma to be detected sooner after treatment. The protein expression profiles of ten oral tongue squamous cell carcinomas and their matched normal mucosal resection margins were examined by two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization-time of flight mass spectroscopy. A number of tumor-associated proteins including heat shock protein (HSP)60, HSP27, alpha B-crystalline, ATP synthase beta, calgranulin B, myosin, tropomyosin and galectin 1 were consistently found to be significantly altered in their expression levels in tongue carcinoma tissues, compared with their paired normal mucosae. The expression profile portrays a global protein alteration that appears specific to oral tongue cancer. The potential of utilizing these tumor related proteins for screening cancer and monitoring recurrence warrants further investigation.postprin
Gravity as Backreaction
Quadratic theory of gravity is a complicated constraint system. We
investigate some consequences of treating quadratic terms perturbatively
(higher derivative version of backreaction effects). This approach is shown to
overcome some well known problems associated with higher derivative theories,
i.e., the physical gravitational degree of freedom remains unchanged from those
of Einstein gravity.
Using such an interpretation of gravity, we investigate a
classical and Wheeler DeWitt evolution of gravity for a
particular sign of , corresponding to non- tachyon case. Matter is
described by a phenomenological . It is concluded that
both the Friedmann potential () and the
Wheeler DeWitt potential () develop repulsive barriers near for
(i.e., ). The interpretations is clear. Repulsive
barrier in implies that a contracting FRW universe ()
will bounce to an expansion phase without a total gravitational collapse.
Repulsive barrier in means that is a classically forbidden
region. Therefore, probability of finding a universe with the big bang
singularity ( ) is exponentially suppressed.Comment: Accepted for publication in Phy. Rev. D.,18 pages, 6 figures, Latex
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Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation
The generation of tunable visible, infrared, and ultraviolet light is examined, along with the control of this light by means of novel mode-locking and modulation techniques. Transient mode-locking of the Nd:YAG laser and generation of short tunable pulses in the visible and the alkali metal inert gas excimer laser systems were investigated. Techniques for frequency conversion of high power and high energy laser radiation are discussed, along with high average power blue and UV laser light sources
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