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61.
Mechanical behaviour of the single B2 phase in the alloy Ti–25Al–25Zr has been studied under compression with different strain rates at elevated temperatures. The alloy Ti–25Al–25Zr exhibits yield strength anomaly similar to those of the typical B2 intermetallics such as FeAl. The stress–strain curves of the alloy tested at 400 °C show type C serrations which are considered to be due to dislocation unlocking. Intersecting and straight slip lines are observed in specimens tested at 400 °C and 600 °C, respectively. 相似文献
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63.
Natural menthol was coated on craft paper by impregnation and studied as volatile corrosion inhibitor for copper in hydrochloric
acid environment. The effect of menthol on copper corrosion was studied by gravimetric and electrochemical methods such as
potentiodynamic polarization and electrochemical impedance measurements. The results indicate that menthol adsorbs on the
metal surface, which protects copper against further corrosion. The adsorption behaviour of menthol on copper surface was
found to obey Temkin’s adsorption isotherm. 相似文献
64.
Deposition of metals and alloys was demonstrated using thermal chemical vapor deposition starting from commercially available precursors in the absence of molecular hydrogen. The adopted chemical strategy relies solely on the selective reactivity of alcohols with metal complexes at deposition temperature. In this report, particular interest was given to the growth of nickel and silver. This process allows the optimization of the growth of single hcp and fcc phases of nickel starting from Ni(acac)2, whereas several silver precursors allow the deposition of the fcc crystalline structure of silver. Steady growth kinetics, without incubation time, was noticed for all investigated precursors. The electrical conductivity of hcp-Ni, fcc-Ni and fcc-Ag shows the typical decay to the bulk value with increased film thickness, and the temperature resistivity coefficients are similar to the corresponding bulk material. 相似文献
65.
Enhancing Data Rates of TH-UWB Systems Using M-ary OPPM-BPSM Modulation Scheme: A System Perspective
Sudhan Majhi A. S. Madhukumar A. B. Premkumar W. Xiang P. Richardson 《Wireless Personal Communications》2011,56(3):583-597
This paper proposes and studies a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio system based on
orthogonal pulse position modulation (OPPM) and biorthogonal pulse shape modulation (BPSM). The proposed scheme offers a high
data rate with satisfactory system performance by using high-level multi-dimensional modulation schemes. It allows one to
increase the number of orthogonal pulses in each pulse position and, consequently, be able to adopt shorter pulse repetition
intervals than those used in conventional M-ary OPPM or M-ary biorthogonal PPM (BPPM) modulation schemes. The performance is analyzed by using characteristic function and Gaussian
approximation in additive white Gaussian and multipath scenarios, respectively. The proposed scheme reduces multiple access
interference considerably in multi-user environments. Finally, simulation results are provided to validate the theoretical
results. 相似文献
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68.
Boron carbide (B4C) added manganese dioxide (MnO2) used as a cathode material for a Zn-MnO2 battery using aqueous lithium hydroxide (LiOH) as the electrolyte is known to have higher discharge capacity but with a lower average discharge voltage than pure MnO2 (additive free). The performance is reversed when using potassium hydroxide (KOH) as the electrolyte. Herein, the MnO2 was mixed with 0, 5, 7 and 10 wt.% of boron carbide during the electrode preparation. The discharge performance of the Zn|LiOH|MnO2 battery was improved by the addition of 5-7 wt.% boron carbide in MnO2 cathode as compared with the pure MnO2. However, increasing the additive to 10 wt.% causes a decrease in the discharge capacity. The performance of the Zn|KOH|MnO2 battery was retarded by the boron carbide additive. Transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy analysis (EDS) results show evidence of crystalline MnO2 particles during discharging in LiOH electrolyte, whereas, manganese oxide particles with different oxygen and manganese counts leading to mixture of phases is observed for KOH electrolyte which is in agreement with X-ray diffraction (XRD) data. The enhanced discharge capacity indicates that boron atoms promote lithium intercalation during the electrochemical process and improved the performance of the Zn|LiOH|MnO2 battery. This observed improvement may be a consequence of B4C suppressing the formation of undesirable Mn(III) phases, which in turn leads to enhanced lithium intercalation. Too much boron carbide hinders the charge carrier which inhibits the discharge capacity. 相似文献
69.
Heat transfer associated with a vapor bubble sliding along a downward-facing inclined heater surface was studied experimentally using holographic interferometry. Volume growth rate of the bubbles as well as the rate of heat transfer along the bubble interface were measured to understand the mechanisms contributing to the enhancement of heat transfer during sliding motion. The heater surface was made of polished silicon wafer (length 185 mm and width 49.5 mm). Experiments were conducted with PF-5060 as test liquid, for liquid subcoolings ranging from 0.2 to 1.2 °C and wall superheats from 0.2 to 0.8 °C. The heater surface had an inclination of 75° to the vertical. Individual vapor bubbles were generated in an artificial cavity at the lower end of the heater surface. High-speed digital photography was used to measure the bubble growth rate. The temperature field around the sliding bubble was measured using holographic interferometry. Heat transfer at the bubble interface was calculated from the measured temperature field. Results show that for the range of parameters considered the bubbles continued to grow, with bubble growth rates decreasing with increasing liquid subcooling. Heat transfer measurements show that condensation occurs on most of the bubble interface away from the wall. For the parameters considered condensation accounted for less than 12% of the rate heat transfer from the bubble base. In this study the heater surface showed no drop in temperature as a result of heat transfer enhancement during bubbles sliding. 相似文献
70.
Kumar M Islam MN Terry FL Freeman MJ Chan A Neelakandan M Manzur T 《Applied optics》2012,51(15):2794-2807
We measure the diffuse reflection spectrum of solid samples such as explosives (TNT, RDX, PETN), fertilizers (ammonium nitrate, urea), and paints (automotive and military grade) at a stand-off distance of 5 m using a mid-infrared supercontinuum light source with 3.9 W average output power. The output spectrum extends from 750-4300 nm, and it is generated by nonlinear spectral broadening in a 9 m long fluoride fiber pumped by high peak power pulses from a dual-stage erbium-ytterbium fiber amplifier operating at 1543 nm. The samples are distinguished using unique spectral signatures that are attributed to the molecular vibrations of the constituents. Signal-to-noise ratio (SNR) calculations demonstrate the feasibility of increasing the stand-off distance from 5 to ~150 m, with a corresponding drop in SNR from 28 to 10 dB. 相似文献