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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - The Role of Trap Symmetry in an Atom-Chip Interferometer above the Bose-Einstein Condensation Threshold
摘要： Cold atom interferometers have demonstrated excellent performance and hold great prospects for time, gravity, acceleration and rotation measurements. Trapped interferometers, for example using atom chips, can potentially enable portable applications of theses sensors. Atom chip interferometers have been successfully demonstrated using Bose-Einstein condensates but are subject to the effect of atom-atom interactions which cause phase decoherence. In this study, we proposed an atom chip interferometer using a gas just above the condensation threshold to reduce the interaction effects. This proposal is similar to white light interferometry in the sense that the difference between the optical paths of the two arms must be close to zero to observe fringes. In a trapped interferometer this condition is analogous to maximizing the degree of symmetry between the two trapping potentials. We demonstrated that if the two trapping potentials are harmonic with slightly different curvatures inhomogeneous dephasing arises. This leads to a typical contrast decay time. Here we use 87Rb in the two states |a>=|F=1,mF=-1> and |b>=|F=2,mF=2>. Both states are trapped by the same magnetic field created by an atom chip. As described by the Breit-Rabi formula, the energies of the two levels |a> and |b> have a slightly different magnetic field dependence. We can use this difference to fine tune the curvature difference between the two trapping potentials. We perform Ramsey sequences and record the fringes as a function of the Ramsey time for several temperatures and values of curvature difference. We find a good agreement with the above formula. Coherence times of order 1s have been observed. We will describe the experiment, the model used to extract the contrast decay time and the limitations of this model due to atom interactions. The results open the way for experimental demonstration of atom chip accelerometers and gyroscopes.
关键词： trap symmetry,Ramsey sequences,atom-chip interferometer,Bose-Einstein condensation,coherence times
更新于2025-09-11 14:15:04
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Renewable and Sustainable Composites || Methodologies for Achieving 1D ZnO Nanostructures Potential for Solar Cells
摘要： One-dimensional (1D) nanostructures are generally used to describe large aspect ratio rods, wires, belts, and tubes. The 1D ZnO nanostructures have become the focus of research owing to its unique physical and technological significance in fabricating nanoscale devices. When the radial dimension of the 1D ZnO nanostructures decreases to some lengths (e.g., the light wavelength, the mean of the free path of the phonon, Bohr radius, etc.), the effect of the quantum mechanics is definitely crucial. With the large surface-to-volume ratio and the confinement of two dimensions, 1D ZnO nanostructures possess the captivating electronic, magnetic, and optical properties. Furthermore, 1D ZnO nanostructure’s large aspect ratio, an ideal candidate for the energy transport material, can conduct the quantum particles (photons, phonons, electrons) to improve the relevant technique applications. To date, many methods have been developed to synthesize 1D ZnO nanostructures. Therefore, methodologies for achieving 1D ZnO nanostructures are expressed, and the relevant potential application for solar cells are also present to highlight the attractive property of 1D ZnO nanostructures.
关键词： hydrothermal,nanostructures,one dimensional,ZnO,solar cell,chemical vapor transport and condensation (CVTC),vapor-liquid-solid (VLS),electrochemical,metal-organic chemical vapor deposition (MOCVD),chemical vapor deposition (CVD)
更新于2025-09-11 14:15:04
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Excitonic Tunneling in the AB-bilayer Graphene Josephson Junctions
摘要： We have considered the AB-stacked bilayer graphene tunnel junction construction. The bilayers are supposed to be in the charge equilibrium states and at the half-filling in each of the electronic layers of the construction and at each value of the external gate potential. By considering the interacting bilayers in both sides of the junction and by taking into account both intralayer and interlayer Coulomb interaction effects, we have calculated the normal and excitonic tunnel currents through the junction. The electronic band renormalizations have been taken into account, due to the excitonic pairing effects and condensation in the BLGs. The exact four-band energy dispersions, including the excitonic renormalizations, have been used for the bilayers without any low-energy approximation. The normal and excitonic tunneling currents have been calculated for different values of the gate potential and for different values of the interlayer interaction parameters in both sides of the tunnel junction. We demonstrate the existence of the excitonic Josephson current through the junction which persist even for the non-interacting bilayer graphene junction. For the non-interacting case, the mechanism of the excitonic condensates formation and tunneling between the condensates is attributed to the interlayer hopping between the layers. The role of the charge neutrality point has been discussed in details.
关键词： Exciton condensation,Excitonic pairing,Josephson junction,Bilayer graphene
更新于2025-09-10 09:29:36
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[Energy, Environment, and Sustainability] Advances in Solar Energy Research || Experimental Investigation into the Applicability of Nanoparticles in Purification of Sewage Water Through Usage of Solar Energy
摘要： In recent years, solar energy driven water desalination/puri?cation systems have been extensively researched with the objective of improving the distillate yield. In these conventional solar driven systems, solar energy heats the water indirectly i.e. in these systems the solar energy is transferred to the water through conduction, resulting in evaporation and hence puri?cation of the water. The present work explores the idea of adding nanoparticles into the wastewater so that solar energy is transferred to water volumetrically, which considerably improves the evaporation rate. Amorphous carbon nanoparticles have been used owing to their high solar weighted absorptivity values. Careful experiments have been carried out to quantify the effect of nanoparticles on the evaporation rate. It was found that optimum level of nanoparticles addition could actually enhance the evaporation rates of the sewage water by *15%. Furthermore, total dissolved solids (TDS) and pH measurements showed considerable improvements, the values being in the range to qualify for drinkable water.
关键词： Evaporation,Nanoparticles,Condensation,Solar energy,Sewage water
更新于2025-09-10 09:29:36
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Photoluminescence properties of the entire excitonic series in
摘要： We investigated the photoluminescence spectra of Cu2O under photoexcitation at 3.05 eV across the violet band gap. The following three features were found: photoluminescence from blue and violet excitons; photoluminescence from yellow excitons of s, d, and f states in addition to p states with a quantum number up to ten; and emissions associated with the inelastic collision of the 1s yellow excitons. The first process is relevant for the separation of radiative and nonradiative decay rates. The second process likely indicates radiative enhancement of high Rydberg yellow excitons. The last process verifies up-conversion of 1s yellow paraexcitons into higher Rydberg states, which is a critical factor impeding the realization of a high-density paraexciton gas towards transition to the Bose-Einstein condensation.
关键词： photoluminescence,Rydberg states,excitons,Bose-Einstein condensation,Cu2O
更新于2025-09-10 09:29:36
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Novel asymmetrical phenothiazine for fluorescent detection of cyanide anions
摘要： Novel asymmetrical phenothiazine (PTZ) bearing 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)-malononitrile (OIM) moiety as the cyanide receptor was synthesized. The sensor fluorophore displayed an intramolecular charge transfer (ICT) electronic absorption peak at 500 nm and fluorescence peak at 576 nm in CH3CN:H2O (90:10) solution. When running a titration of the prepared phenothiazine fluorophore with a range of concentrations of cyanide, the electronic absorption and fluorescence peaks diminish in a ratio-metric mode. This can be attributed to the nucleophilic Michael-attack of cyanide anion at the α-position of the oxoindenylidenemalononitrile vinyl moiety of the fluorophore. This results in switching such electron acceptor to anionic electron donor and thus breaking the conjugated molecular system, which eventually influence the ICT and the emission peak position of the fluorophore. It was found that the fluorescent sensor displayed high sensitivity with a rapid responding time as low as than 50 second. A high selectivity was also detected toward cyanide ion at a recognition limit as low as 3.2 × 10?9 mol L-1.
关键词： Cyanide,Fluorescence,Phenothiazine,Nucleophilic addition,Knoevenagel condensation
更新于2025-09-10 09:29:36
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Bose Condensation of Long-Living Direct Excitons in an Off-Resonant Cavity
摘要： We propose a way to increase the lifetime of two-dimensional direct excitons and show the possibility to observe their macroscopically coherent state at temperatures much higher than that of indirect exciton condensation. For a single GaAs quantum well embedded in photonic layered heterostructures with subwavelength period, we predict the exciton radiative decay to be strongly suppressed. Quantum hydrodynamics joined with the Bogoliubov approach are used to study the Berezinskii-Kosterlitz-Thouless crossover in a finite exciton system with intermediate densities. Below the estimated critical temperatures, drastic growth of the correlation length is shown to be accompanied by a manyfold increase of the photoluminescence intensity.
关键词： Bogoliubov approach,Berezinskii-Kosterlitz-Thouless crossover,Bose condensation,direct excitons,quantum hydrodynamics,off-resonant cavity
更新于2025-09-09 09:28:46
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Porous graphitic carbon nitride with controllable nitrogen vacancies: As promising catalyst for enhanced degradation of pollutant under visible light
摘要： Carbon nitride (CN) materials are considered as promising photocatalysts due to the advantages of easy availability and visible light absorption. However, wide band gap and high recombination rates of electron-hole pairs of conventional CN materials remain the “bottleneck” of the photocatalysts. Therefore, it is necessary to develop an efficient strategy to narrow band gap of CN and accelerate its charge transfer. In addition, the introduction of nitrogen (N) vacancies is an efficient strategy to narrow band gap and reduce recombination rates of electron-hole pairs. Herein, a novel triazole ring-based graphite carbon nitride (g-C3N5) is developed by one step pathway of NaOH-assisted condensation of triazole rings for the first time. It is found that NaOH can control N vacancies and band gap of g-C3Nx. Meanwhile, the N vacancies of g-C3Nx gradually increase with the increasing concentration of NaOH in the range of 0.005-0.1 g, suppressing the recombination of photogenerated electron-hole pairs. The proposed g-C3Nx exhibits outstanding photocatalytical and photoelectrochemical performance. Therefore, the study highlights the significance of N vacancies in enhancing the photocatalytical and photoelectrochemical performance of promising g-C3N5.
关键词： outstanding photocatalytical and photoelectrochemical performance,g-C3N5,NaOH-treated condensation of triazole rings,controllable N vacancies
更新于2025-09-09 09:28:46
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Regioisomeric synthesis of chlorin-e6 dimethyl esters and their optical properties
摘要： Chlorin-e6 dimethyl esters possessing a single carboxy group at the 13-, 151-, or 172-position were prepared by chemically modifying chlorophyll-a. These three synthetic regioisomers were fully characterized by their mass, NMR, and visible absorption spectra. Their molecular structures were unambiguously identified by the specific 1H–13C correlation at the 13-, 15-, and/or 17-substituents in their respective HMBC spectra. Methyl esterification of 13/151-COOH and hydrolysis of 13/151-COOMe affected small shifts of the Qy absorption and fluorescence emission maxima in a diluted CH2Cl2 solution, while no substitution effect of 172-COOH/Me was observed.
关键词： fluorescence emission,ester protection,Qy absorption,retro-Dieckmann condensation,chlorophyll-a derivative
更新于2025-09-09 09:28:46
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ALMA observations of TiO <sub/>2</sub> around VY CMa
摘要： Titanium dioxide, TiO2, is a refractory species that could play a crucial role in the dust-condensation sequence around oxygen-rich evolved stars. We present and discuss the detections of 15 emission lines of TiO2 with ALMA in the complex environment of the red supergiant VY CMa. The observations reveal a highly clumpy, anisotropic out?ow in which the TiO2 emission likely traces gas exposed to the stellar radiation ?eld. We ?nd evidence for a roughly east-west oriented, accelerating bipolar-like structure, of which the blue component runs into and breaks up around a solid continuum component. We see a distinct tail to the south-west for some transitions, consistent with features seen in the optical and near-infrared. We ?nd that a signi?cant fraction of TiO2 remains in the gas phase outside the dust-formation zone and suggest that this species might play only a minor role in the dust-condensation process around extreme oxygen-rich evolved stars like VY CMa.
关键词： oxygen-rich evolved stars,ALMA,dust-condensation,TiO2,VY CMa
更新于2025-09-09 09:28:46