New transformation of Wigner operator in phase space quantum mechanics for the two-mode entangled case

As a natural extension of Fan's paper (arXiv: 0903.1769vl [quant-ph]) by employing the formula of operators' Weyl ordering expansion and the bipartite entangled state representation we find new two-fold complex integration transformation about the Wigner operator (in its entangled form) in phase space quantum mechanics and its inverse transformation. In this way, some operator ordering problems can be solved and the contents of phase space quantum mechanics can be enriched.Comment: 8 pages, 0 figure

Negative refraction in nonlinear wave systems

People have been familiar with the phenomenon of wave refraction for several centuries. Recently, a novel type of refraction, i.e., negative refraction, where both incident and refractory lines locate on the same side of the normal line, has been predicted and realized in the context of linear optics in the presence of both right- and left-handed materials. In this work, we reveal, by theoretical prediction and numerical verification, negative refraction in nonlinear oscillatory systems. We demonstrate that unlike what happens in linear optics, negative refraction of nonlinear waves does not depend on the presence of the special left-handed material, but depends on suitable physical condition. Namely, this phenomenon can be observed in wide range of oscillatory media under the Hopf bifurcation condition. The complex Ginzburg-Landau equation and a chemical reaction-diffusion model are used to demonstrate the feasibility of this nonlinear negative refraction behavior in practice

Crumpling wires in two dimensions

An energy-minimal simulation is proposed to study the patterns and mechanical properties of elastically crumpled wires in two dimensions. We varied the bending rigidity and stretching modulus to measure the energy allocation, size-mass exponent, and the stiffness exponent. The mass exponent is shown to be universal at value $D_{M}=1.33$. We also found that the stiffness exponent $\alpha =-0.25$ is universal, but varies with the plasticity parameters $s$ and $\theta_{p}$. These numerical findings agree excellently with the experimental results

Creating stable molecular condensate using a generalized Raman adiabatic passage scheme

We study the Feshbach resonance assisted stimulated adiabatic passage of an effective coupling field for creating stable molecules from atomic Bose condensate. By exploring the properties of the coherent population trapping state, we show that, contrary to the previous belief, mean-field shifts need not to limit the conversion efficiency as long as one chooses an adiabatic passage route that compensates the collision mean-field phase shifts and avoids the dynamical unstable regime.Comment: 4+\epsilon pages, 3 figure

Effects of direct injection timing of ethanol fuel on engine knock and lean burn in a port injection gasoline engine

Ethanol is a promising alternative fuel for internal combustion engines due to its renewable feature. To make the use of ethanol fuel more effective and efficient, ethanol direct injection plus gasoline port injection (EDI + GPI) has been investigated in recent years. By directly injecting ethanol into the engine, the advantages of ethanol fuel such as high latent heat of vaporization, fast laminar flame speed, wide flammability and better low temperature combustion stability can be well utilized to enhance engine anti-knock ability and improve lean burn performance. For an engine equipped with direct injection (DI) system, start of injection (SOI) timing is an important control parameter which directly affects the engine performance. This paper reports the investigation to the effect of ethanol fuel SOI timing on knock mitigation and lean burn. Experiments were conducted on a 250 cc single cylinder spark ignition (SI) engine equipped with EDI + GPI system. Ethanol fuel SOI timing before and after the inlet valve closing, defined as early and late injection timings (EEDI and LEDI) were investigated in engine conditions at knock limited spark advance (KLSA) and lean burn limit. The experimental results showed that LEDI was effective on suppressing engine knock and permitting more advanced spark timing. EEDI was less effective than LEDI on mitigating knock due to the increased heat transfer from cylinder wall to gases. The mixture quality may be deteriorated in LEDI conditions which resulted in low engine efficiency and high emissions. Volumetric efficiency was increased and combustion duration was reduced in EEDI conditions. The combined effects of improved volumetric efficiency, reduced combustion duration and moderately advanced spark timing resulted in increased engine thermal efficiency in EEDI conditions. In lean burn, EEDI was more effective on extending lean burn limit. The maximum lambda achieved in EEDI condition was 1.29 when ethanol energy ratio (EER) was 24% and SOI timing was 290 CAD BTDC. LEDI only slightly increased lean burn limit which was just over stoichiometric air-fuel ratio (AFR). In EEDI conditions, IMEP was greater and combustion stability (COV) was better than that in LEDI conditions. The emissions in EEDI conditions were also lower than that in LEDI conditions. © 2014 Elsevier Ltd. All rights reserved

An Investigation of the Performance of a Gasoline Spark Ignition Engine Fuelled with Hot Ethanol Direct Injection

Ethanol direct injection (EDI) is a promising technology to address the issue of knock in downsized spark ignition (SI) engines due to the strong cooling effect of EDI and ethanol’s large octane number. However, the evaporation rate of ethanol is lower than that of gasoline fuel because of its low volatility (saturation vapour pressure) in low temperature conditions and large enthalpy of vaporization. This might have caused the increased HC and CO emissions in an ethanol direct injection plus gasoline port injection (EDI+GPI) engine when EDI was applied. To address this issue, the combustion and emission performance of an EDI+GPI engine fuelled with hot ethanol fuel was experimentally investigated in the present study. The experiments were conducted on a 249 cc single cylinder SI engine at medium load (IMEP 6.0-6.3 bar) and stoichiometric fuel/air ratio condition. The injected ethanol fuel temperature ranged from 45 ℃ (no fuel heating) to 105 ℃ (flash-boiling spray) with an increment of 15 ℃. Experimental results showed that the IMEP decreased slightly with the increase of ethanol fuel temperature. However, the ISCO and ISHC emissions decreased significantly and ISNO increased moderately with the increase ethanol fuel temperature

Investigation of the effect of heated ethanol fuel on combustion and emissions of an ethanol direct injection plus gasoline port injection (EDI + GPI) engine

© 2016 Elsevier Ltd Ethanol direct injection plus gasoline port injection (EDI + GPI) is a new technology to utilise ethanol fuel more efficiently and flexibly in spark ignition engines. One issue needs to be addressed in the development of EDI + GPI is the ethanol fuel's low vapour pressure and large latent heat which slow down the ethanol's evaporation and result in the mixture unready for combustion by the time of spark ignition and the consequent increase of CO and HC emissions. Heating the ethanol fuel to be directly injected (EDI heating) has been proposed to address this issue. This paper reports the investigation of the effect of EDI heating on the combustion and emissions of a research engine equipped with EDI + GPI. The results showed that EDI heating effectively reduced the CO and HC emissions of the engine due to the increase of evaporation rate and reduced fuel impingement and local over-cooling. The reduction of CO and HC became more significant with the increase of ethanol ratio. When the temperature of the ethanol fuel was increased by 40 °C, the CO and HC were reduced by as much as 43% and 51% respectively in EDI only condition at the original spark timing of 15 CAD BTDC, and 15% and 47% respectively at the minimum spark advance for best torque (MBT) timing of 19 CAD BTDC. On the other hand, the NO emission was slightly increased, but still much smaller than that in GPI only condition due to the strong cooling effect and low combustion temperature of EDI. The IMEP and combustion speed were slightly reduced by EDI heating due to the decrease of injector fuel flow rate and spray collapse of flash-boiling. The largest decrease of IMEP was 5% at the original spark timing and 3% at the MBT timing. Moreover, at the MBT timing, the IMEP increased continuously with the increase of ethanol ratio in the entire range from 0% to 100%. This indicated that the decrease of IMEP in high ethanol ratio conditions at the original spark timing could be avoided by adjusting the spark timing. Therefore EDI heating is effective to address the issues of ethanol's low evaporation rate in low temperature engine environment and over-cooling effect at high ethanol ratio condition in the development of EDI + GPI engine

Achieving ground-state polar molecular condensates by chainwise atom-molecule adiabatic passage

We generalize the idea of chainwise stimulated Raman adiabatic passage (STIRAP) [Kuznetsova \textit{et al.} Phys. Rev. A \textbf{78}, 021402(R) (2008)] to a photoassociation-based chainwise atom-molecule system, with the goal of directly converting two-species atomic Bose-Einstein condensates (BEC) into a ground polar molecular BEC. We pay particular attention to the intermediate Raman laser fields, a control knob inaccessible to the usual three-level model. We find that an appropriate exploration of both the intermediate laser fields and the stability property of the atom-molecule STIRAP can greatly reduce the power demand on the photoassociation laser, a key concern for STIRAPs starting from free atoms due to the small Franck-Condon factor in the free-bound transition.Comment: 8 pages, 2 figures, to appear in Phy. Rev.