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Projector-based renormalization approach to electron-hole-photon systems in their nonequilibrium steady state
摘要： We present an extended version of the projector-based renormalization method that can be used to address not only equilibrium but also nonequilibrium situations in coupled fermion-boson systems. The theory is applied to interacting electrons, holes, and photons in a semiconductor microcavity, where the loss of cavity photons into vacuum is of particular importance. The method incorporates correlation and fluctuation processes beyond mean-field theory in a wide parameter range of detuning, Coulomb interaction, light-matter coupling, and damping, even in the case when the number of quasiparticle excitations is large. This enables the description of exciton and polariton formation and their possible condensation through spontaneous phase symmetry breaking by analyzing the ground-state, steady-state, and spectral properties of a rather generic electron-hole-photon Hamiltonian, which also includes the coupling to two fermionic baths and a free-space photon reservoir. Thereby, the steady-state behavior of the system is obtained by evaluating expectation values in the long-time limit by means of the Mori-Zwanzig projection technique. Tracking and tracing different order parameters, the fully renormalized single-particle spectra and the steady-state luminescence, we demonstrate the Bose-Einstein condensation of excitons and polaritons and its smooth transition when the excitation density is increased.
关键词： exciton condensation,nonequilibrium steady state,semiconductor microcavity,projector-based renormalization method,electron-hole-photon systems,Bose-Einstein condensation,polariton condensation
更新于2025-09-23 15:23:52
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Survey of Object-Based Data Reduction Techniques in Observational Astronomy
摘要： Dealing with astronomical observations represents one of the most challenging areas of big data analytics. Besides huge variety of data types, dynamics related to continuous data flow from multiple sources, handling enormous volumes of data is essential. This paper provides an overview of methods aimed at reducing both the number of features/attributes as well as data instances. It concentrates on data mining approaches not related to instruments and observation tools instead working on processed object-based data. The main goal of this article is to describe existing datasets on which algorithms are frequently tested, to characterize and classify available data reduction algorithms and identify promising solutions capable of addressing present and future challenges in astronomy.
关键词： feature extraction,astronomy,dimensionality reduction,big data,data condensation
更新于2025-09-23 15:23:52
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Resonance Tunneling Phenomena in Two-Dimensional Multilayer van der Waals Crystalline Systems
摘要： Works, mostly experimental, concerning the most interesting features of application of the resonant tunneling spectroscopy to a new type of heterosystems, van der Waals heterostructures, have been briefly reviewed. These heterostructures appeared after the recent discovery of two-dimensional crystals, which are a new class of materials beginning with graphene. The role of the angular matching of crystal lattices of conducting graphene electrodes of van der Waals systems in carrier tunneling between them has been analyzed together with the closely related problems of satisfaction of conservation laws in tunneling transitions. Manifestations of multiparticle correlation interactions between carriers in van der Waals systems such as Wigner crystallization of electrons in a two-dimensional electron gas in a magnetic field and Bose condensation of excitons in parallel two-dimensional electron gases have been briefly discussed.
关键词： angular matching,momentum conservation,resonant tunneling spectroscopy,graphene,two-dimensional crystals,Wigner crystallization,van der Waals heterostructures,Bose condensation
更新于2025-09-23 15:23:52
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Accurate Number Densities of Ideal Photons in a One-Dimensional Barrel Cavity
摘要： Our experimental scheme is based on a barrel optical microcavity filled with a dye solution. It is found that the number of non-condensed photons is characterized by an analytical function, which involves a q-digamma function in mathematics. We employ the q-digamma function to calculate the spatial and momentum distributions of ideal photons in a one-dimensional barrel cavity. The first main finding in this paper is that the spatial and momentum distributions possess a similar profile. The second main finding is that when photons are in the normal state, the density profile exhibits Friedel oscillations. The third main finding is that when photons are in the BEC state, the density profile exhibits a sharp peak with extremely narrow width. The fourth main finding is that the central peak of the density distribution is a monotonically increasing function of the photon number N but is a monotonically decreasing function of the temperature T.
关键词： Bose-Einstein condensation,One-dimensional photons,Number densities of photons,Optical microcavity
更新于2025-09-23 15:23:52
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Optical responses of BSA protein under re-entrant condensation in presence of trivalent ions
摘要： Fluorescence behavior of globular protein like BSA is studied under the re-entrant condensation in the presence of trivalent salts like YCl3 and LaCl3. BSA shows a re-entrant behaviour in solution where a specific turbid phase is formed between the two critical concentrations of the trivalent salts. Optical behaviours of proteins are explored by UV-Vis, photoluminescence and time resolved photoluminescence (TRPL) spectroscopy, whereas hydrodynamic size is obtained from the dynamic light scattering (DLS) technique. BSA shows maximum emission intensity at ≈ 338 nm for an excitation at 278 nm, however, the value of the peak intensity of emission gradually increases with the increase in salt concentration and becomes maximum at the turbid phase but for higher salt concentration as the re-dissolution takes place the emission intensity again decreases. TRPL study suggests that the decay time of BSA under re-entrant condensation is correlated with the salt concentration, whereas DLS study shows that the hydrodynamic size gradually increases up to a certain salt concentration where turbid phase is formed and then again decreases for higher salt concentrations. The variation of emission intensity of BSA nearly follows the modification of diffusion coefficient or hydrodynamic size and the phase transition behaviours.
关键词： UV-Vis spectroscopy,Bovine serum albumin,Tri-valent ions,Re-entrant condensation,Fluorescence spectroscopy
更新于2025-09-23 15:23:52
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On-line measurement of fluorescent aerosols near an industrial zone in the Yangtze River Delta region using a wideband integrated bioaerosol spectrometer
摘要： In this work, we present on-line fluorescent aerosol measurements by the wideband integrated bioaerosol spectrometer (WIBS-4A) near an industrial zone in Nanjing, a megacity in the Yangtze-River-Delta (YRD) region. The fieldwork was conducted from April 1 to May 8, 2014. A TSI. 3321 aerosol-particle-sizer (APS) was simultaneously deployed to measure the total number size distribution of aerosol with diameter from 0.8–20 μm. Both WIBS-4A and APS reported similar number concentration and temporal profiles (R2 = 0.72). However, the daily average number of potential bioaerosols was only 0.5 ± 0.2% of the total particles detected by the WIBS-4A and displayed a completely different diurnal profile from that of APS. In addition, WIBS-4A can only provide integrated fluorescent signals, which strongly limited the potential to specifically identify the bioaerosols. Accordingly, hierarchical-agglomerative-cluster-analysis (HACA) was utilized to identify and speciate the potential bioaerosols from the WIBS-4A dataset. By maximizing the total distances among all potential cluster centers, a 12-cluster solution was accepted as the optimum result. These clusters were further identified according to their fluorescent signatures, size, and morphology, i.e., non-bioaerosols, bacteria, and fungal spores and/or pollen fragments. Bacteria were the dominant bioaerosol species detected in this work. The diurnal profiles of bioaerosols correlated very well with relatively humidity (RH), reaching daily maxima around 3 AM~6 AM, indicating the presence of humidity controlled bioaerosol emission mechanism, i.e., bacteria may flourish under moderate ambient temperature, RH, and the absence of UV radiation. The size- and AF-distributions of bioaerosols indicated that bioaerosols normally varied substantially in size and assumed a rather irregular shape. Although the number concentration of bioaerosols was relatively small, most bioaerosols can efficiently serve as ice nuclei by providing rough and irregular surfaces, verified by the observation results. Therefore, WIBS-4A measurements can still be informative for investigations of bioaerosols in the atmosphere, especially when HACA method was incorporated into the data processing.
关键词： Hierarchical agglomerative cluster analysis,WIBS-4A,Ice nuclei,Cloud condensation nuclei,Primary biological aerosol
更新于2025-09-23 15:23:52
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Thermal Fluctuations in the Phase Structure of the Excitonic Insulator Charge Density Wave State in the Extended Falicov–Kimball Model
摘要： Excitonic insulator (EI) instability accompanied by a charge density wave (CDW) state in the two-dimensional extended Falicov–Kimball model including electron–phonon interaction is investigated by applying the unrestricted Hartree–Fock approximation. Treating both the Coulomb attraction and the electron–phonon coupling on an equal footing, we have derived a set of self-consistent equations, which allows us to determine both the excitonic insulator order parameter and the lattice displacement. The phase structures show us that both the Coulomb interaction and the electron–phonon coupling act together in establishing the EI-CDW state, which typifies either a phononic-CDW or an excitonic-CDW state depending on the competition of the interactions. At a given low temperature, the EI-CDW state is found between two critical values of the Coulomb interaction. The window of the condensation state grows when increasing the electron–phonon coupling. Depending on the temperature and the Coulomb interaction the Bardeen–Cooper–Schrieffer–Bose–Einstein condensation (BCS–BEC) crossover of the EI-CDW state in the systems has been established. Under the effects of phonons, the BCS–BEC crossover deviates to a larger Coulomb interaction while the semimetal–semiconductor transition in the normal state remains.
关键词： semimetal–semiconductor transition,charge density wave,unrestricted Hartree–Fock approximation,Excitonic condensation
更新于2025-09-23 15:23:52
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Novel π-conjugated systems based on pyrimidine N-Oxide
摘要： Pyrimidine N-oxide moiety for the first time was used as a heterocyclic core for the construction of π-conjugated molecules with fluorescent properties. For the synthesis of the title compounds a simple two-step protocol starting from readily available 4-fluoro-2-methylpyrimidine N-oxides was elaborated. A series of 17 novel pyrimidine N-oxide derivatives containing various functional substituents and π-conjugated systems of different length were obtained. The title compounds revealed fluorescent properties in visible region, possessing emission maximum up to 575 nm. Deoxygenation of the N-oxide group led to the loss of visible fluorescence. The chemosensor properties towards TFA and a number of metal cations were demonstrated for 3a, the first representative of the title series. Cytotoxic activity against breast adenocarcinoma cell line was found for three pyrimidine N-oxide derivatives 3b,i,n. Pyrimidine N-oxide 3a was shown to possess excellent biocompatibility and capability to enter cells, that makes it a promising structure for development of bioimaging fluorescent probes.
关键词： Anticancer activity,Pyrimidines,π-Conjugated systems,Fluorescence,Knoevenagel condensation,Metal cations
更新于2025-09-23 15:23:52
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Preparation of Functionalized SiO2 Microspheres by One Step Method
摘要： Functional silica microparticle is a kind of important inorganic non-metallic oxide with a wide range of applications in many fields due to its excellent chemical and thermal stabilities. Post modification is the most common functional method, but, low efficiency. In this paper, a new acid hydrolysis and subsequent alkaline condensation method was developed to prepare SiO2 microspheres with functional groups on surface by condensing or co-condensing functional organosilane precursors (γ-Aminopropyltriethoxysilane (APTES), γ-Mercaptopropyltriethoxysilane (MPTES) and γ-Mercaptopropyltrimethoxysilane (MPTMS) etc) with phenyltrimethoxysilane (PTMS). Series of characterization methods, such as IR, XPS and Raman, demonstrated that the surface of the as-prepared SiO2 microspheres was successfully functionalized with amine or sulfydryl groups. This method may provide a reference for one-step preparation of functional SiO2 microspheres.
关键词： Functionalized SiO2 microspheres,Condensation,One-step method
更新于2025-09-23 15:22:29
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Electrical Transport Properties of Thin Film Composed of a-ZnO Nanorods
摘要： Background: Due to its wide band gap, high exciton binding energy and high breakdown strength, the nanostructures of ZnO may find applications for electronic, photonic devices, and high-frequency applications. Objective: The aim of the present work is to study electrical transport of thin film composed of a-ZnO nanorods. Method: Physical vapour condensation method was employed to fabricate the nanorods of ZnO. The morphology of these nanorods was investigated with the help of scanning electron microscope. X-ray diffraction pattern of as-prepared thin film was recorded using X-ray diffractometer. For dc conductivity measurements, four-probe method was used. Result: The as-prepared ZnO nanorods have diameter ranging from 10-20 nm and the length is of order of few hundred nanometers. XRD pattern of film composed of ZnO nanorods suggests the amorphous nature. Temperature dependence of dc conductivity has been studied over the temperature range of (297- 4.2K). For the temperature range of 297-120K, Mott’s three dimensional variable range hopping (VRH) is applied to explain the electrical conduction. For lower temperature range (120 - 4.2K), 2D-variable-range hopping in localized states near the Fermi level may be responsible for the transport of carriers. Conclusion: Variable range hopping mechanism (VRH) has been suggested for the entire temperature range (298-4.2K) on the basis of temperature dependence of dc conductivity data, which changes from 3D to 2D on moving to lower temperatures side (below 125K).
关键词： physical vapour condensation technique,variable range hopping,XRD,ZnO nanorods,SEM,Mott’s parameters,electrical conduction mechanism
更新于2025-09-23 15:22:29