Thermodynamic properties of non-Hermitian Nambu--Jona-Lasinio models

We investigate the impact of non-Hermiticity on the thermodynamic properties of interacting fermions by examining bilinear extensions to the $3+1$ dimensional $SU(2)$-symmetric Nambu--Jona-Lasinio (NJL) model of quantum chromodynamics at finite temperature and chemical potential. The system is modified through the anti-$PT$-symmetric pseudoscalar bilinear $\bar{\psi}\gamma_5 \psi$ and the $PT$-symmetric pseudovector bilinear $iB_\nu \,\bar{\psi}\gamma_5\gamma^\nu \psi$, introduced with a coupling $g$. Beyond the possibility of dynamical fermion mass generation at finite temperature and chemical potential, our findings establish model-dependent changes in the position of the chiral phase transition and the critical end-point. These are tunable with respect to $g$ in the former case, and both $g$ and $|B|/B_0$ in the latter case, for both lightlike and spacelike fields. Moreover, the behavior of the quark number, entropy, pressure and energy densities signal a potential fermion or antifermion excess compared to the standard NJL model, due to the pseudoscalar and pseudovector extension respectively. In both cases regions with negative interaction measure $I = \epsilon-3p$ are found. Future indications of such behaviors in strongly interacting fermion systems, for example in the context of neutron star physics, may point toward the presence of non-Hermitian contributions. These trends provide a first indication of curious potential mechanisms for producing non-Hermitian baryon asymmetry. In addition, the formalism described in this study is expected to apply more generally to other Hamiltonians with four-fermion interactions and thus the effects of the non-Hermitian bilinears are likely to be generic.Comment: 39 pages, 15 figure

Vibration analysis of a small diesel engine using diesel-biodiesel fuel blends

Biodiesel as an environmentally friendly fuel has the potential to provide comparable engine performance results.  Biodiesel is a renewable fuel produced from vegetable and seed oils, animal fats or waste edible oils.  Sound and vibration caused by the combustion process in the engine might have direct effects on users.   One of the important characteristics of diesel fuels is high noise and vibration.  The present study was carried out to examine the vibration of different diesel-biodiesel fuel blends in power tiller engine.  The main goal was to present fuels with the minimum vibration.  So, the time domain signals were analyzed in five levels of engine speed, three axes and six fuel blends on the engine.  The signal processing and statistical approach were applied for data analysis.  The results showed that in all engine speeds, the dominant frequency is matched to the piston stroke frequency of the engine, as well as the frequency of vibration with the increase of engine speed.  The experiments indicated that the magnitude of vibration in the power tiller engine depends on the axis of measurement, engine speed and the fuel blends.  Vibration acceleration is significantly affected by engine speed and the increase in forward speed due to the increase in vibration acceleration rms.  The results of the experiments revealed that vibration acceleration is significantly affected by the axis of measurement.  The magnitude of vibration acceleration in vertical axis was more than that in the other two axes and magnitude of vibration acceleration in the longitudinal axis was more than that in the lateral axis.  Fuel blends had significant effect on the vibration.  It demonstrated that B100, B5 and B20 have the lowest vibration.  On the contrary, B15 and B10 have the highest vibration.   Keywords: vibration analysis, power tiller, time domain, frequency domain, diesel-biodiesel fuel blend

Coordination mechanism of cyanine dyes on the surface of core@active shell β-NaGdF4:Yb3+,Er3+ nanocrystals and its role in enhancing upconversion luminescence

The sensitization of lanthanide-doped upconversion nanocrystals (UCNCs) using organic dyes with a broad and intense optical absorption is an interesting approach for efficient excitation-energy harvesting and enhancing the upconversion luminescence of such UCNCs. In this work, an ultrasmall (similar to 6.5 nm in diameter) beta-NaGdF4:Yb3+,Er3+ core and related core@shell UCNCs were sensitized using six NIR-excitable cyanine dyes with a wide range of functional groups and optical properties. The greatest UC enhancement of 680-times was observed for the conjugate between the Cy 754 dye and NaGdF4:Yb3+,Er3+@NaGdF4:10%Yb3+,30%Nd3+ core@shell UCNCs excited using a 754 nm laser. The enhancement was estimated relative to NaGdF4:Yb3+,Er3+@NaGdF4:10%Yb3+,30%Nd3+ core@shell UCNCs capped with oleic acid and excited using a similar intensity (75 W cm(-2)) of a 980 nm laser. UC intensity measurements for identical dye-sensitized UCNCs carried out in methanol and in deuterated methanol under argon, as well as in air, allowed us to reveal the connection of the dye triplet states with UCNC sensitization as well as of the hydroxyl groups with quenching of the excited states of lanthanide ions. For UCNCs dispersed in methanol, the strong quenching UC luminescence was always observed, including core@shell UCNCs (with a shell of similar to 2 nm). A strong influence of the triplet states of the dyes was observed for the two dyes Cy 754 and Cy 792 that bind firmly to UCNCs and allow the distances between the dye and the UCNC to be reduced, whereas the contribution of this sensitization pathway is very insignificant for Cy 740 and Cy 784 dyes that bind weakly to UCNCs

Coordination mechanism of cyanine dyes on the surface of core@active shell β-NaGdF4_{4}:Yb3+^{3+},Er3+^{3+} nanocrystals and its role in enhancing upconversion luminescence

The sensitization of lanthanide-doped upconversion nanocrystals (UCNCs) using organic dyes with a broad and intense optical absorption is an interesting approach for efficient excitation-energy harvesting and enhancing the upconversion luminescence of such UCNCs. In this work, an ultrasmall (∼6.5 nm in diameter) β-NaGdF$_{4}$:Yb$^{3+}$,Er$^{3+}$ core and related core@shell UCNCs were sensitized using six NIR-excitable cyanine dyes with a wide range of functional groups and optical properties. The greatest UC enhancement of 680-times was observed for the conjugate between the Cy 754 dye and β-NaGdF$_{4}$:Yb$^{3+}$,Er$^{3+}$@NaGdF$_{4}$:10%Yb$^{3+},30$^{3+} core@shell UCNCs excited using a 754 nm laser. The enhancement was estimated relative to NaGdF$_{4}$:Yb$^{3+}$,Er$^{3+}$@NaGdF$_{4}$:10%Yb$^{3+},30$^{3+} core@shell UCNCs capped with oleic acid and excited using a similar intensity (75 W cm$^{-2}$) of a 980 nm laser. UC intensity measurements for identical dye-sensitized UCNCs carried out in methanol and in deuterated methanol under argon, as well as in air, allowed us to reveal the connection of the dye triplet states with UCNC sensitization as well as of the hydroxyl groups with quenching of the excited states of lanthanide ions. For UCNCs dispersed in methanol, the strong quenching UC luminescence was always observed, including core@shell UCNCs (with a shell of ∼2 nm). A strong influence of the triplet states of the dyes was observed for the two dyes Cy 754 and Cy 792 that bind firmly to UCNCs and allow the distances between the dye and the UCNC to be reduced, whereas the contribution of this sensitization pathway is very insignificant for Cy 740 and Cy 784 dyes that bind weakly to UCNCs