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[en] Heat leakage is an important parameter to reflect heat insulated performance of cryogenic vessel. According to the current standard requirements, it needs to measure the daily evaporation rate to indicate heat leakage. The test needs-over 24h after cryogenic vessel in heat equilibrium as standard required, therefore test efficiency is poor and new efficient method is required to cut test time. First of all, the volume of instantaneous evaporated gas and heat leakage are calculated by the current standard corresponding to the maximum allowable daily evaporation rate of cryogenic vessel. Depending on the relationship between real daily evaporation rate and maximum allowable daily evaporation rate of cryogenic vessel, we designed a new test method based on the pressure changes over time in cryogenic vessel to determine whether its heat insulated performance meets requirements or not. Secondly, the heat transfer process was analyzed in measurement of cryogenic vessel, and the heat transfer equations of whole system were established. Finally, the test was completed in four hours; meanwhile the heat leakage and daily evaporation rate of cryogenic vessel are calculated basing on test data
[en] The neutron halo nucleus has been vigorously studied as a unique entity that appears near the neutron drip line. Taking advantage of the difference in sensitivity between Coulomb breakup reaction and nuclear force breakup reaction, the authors performed nuclear spectroscopic studies on 37Mg and 29Ne nuclei near the neutron drip line, and identified that these ground states have p-wave halo structure. Furthermore, for 37Mg, they determined the spin parity and neutron separation energy of the ground state for the first time, and for 29Ne, determined the spin parity of the ground state. (A.O.)
[en] Biexcitons localized at ZnCdS quantum dots (x = 0.37 or 0.45) with a diameter of ~ 45 Å synthesized by two different methods were studied by femtosecond laser spectroscopy. The spectral features of ultrafast transient absorption spectra at the short-time delay of 70 fs are associated with the three lowest energy transitions of quantum dots. The shapes of the transient absorption bands were modeled by fitting to linear absorption. The spectral positions of the absorption components of the excited state in the transient spectra take into account the energy of the biexciton coupling. By fitting the experimental transient absorption spectra of ZnCdS QDs, the binding energies of biexcitons were determined. The biexciton binding energies vary from 16.6 to 37 meV depending on the biexciton transition excited at the ZnCdS quantum dot.
[en] In this paper, we have investigated the thermally activated carriers transfer mechanism in closely stacked InAs/GaAs quantum dots (QDs) by means of steady-state photoluminescence (PL) and time-resolved photoluminescence measurements. The 10 K PL spectrum exhibits double-emission peaks where the excitation power dependence reveals that these emission peaks are attributed to large and small QD groups. With increasing the sample temperature, an abnormal line-width shrinkage of large QDs (LQDs) is observed. The increase in PL decay lifetime of LQDs versus temperature is nicely explained as the electron and hole wave function overlap between dot layers induced by vertical electronic coupling effect. Using a thermal escape model, the activation energies for PL thermal quenching at high temperatures (above 80K) were derived from fitting the temperature-dependent PL decay lifetime data of LQDs and SQDs. The determined activation energies show that the escape of electron-hole pairs from QDs occurs via transfer channel located below the wetting layer. These results are well reproduced by a rate equation-based model treating the QDs as a localized-state ensemble. Our results emphasize the important role of the vertically stacked InAs/GaAs QDs structures with thin GaAs spacer layer to slow down the carrier PL decay lifetime of the thermal transfer process between QDs. This finding is important for the use of such structures as intermediate band in solar cells.
[en] In our previous papers (Can. J. Phys. 91 (2013) 715; 92 (2014) 1405), we studied Rydberg states of systems consisting of a nucleus of charge Z, a muon, and an electron, both the muon and electron being in circular states. The studies of such quasimolecules μZe were motivated by numerous applications of muonic atoms and molecules, where one of the electrons is substituted by the heavier lepton μ-. We demonstrated that the muonic motion can represent a rapid subsystem, while the electronic motion can represent a slow subsystem. We showed that the spectral lines emitted by the muon in such systems experience a red shift compared to the corresponding spectral lines that would have been emitted by the muon in a muonic hydrogenic atom/ion. In the present paper, we also consider Rydberg states of quasimolecules μZe with Z > 1 (i.e., Rydberg states of muonic-electronic helium and helium-like ions). However, our current approach has important distinctions from our previous papers. The systems considered here are truly stable and the electron orbit is generally elliptical (although the relatively small influence of the electron on the muon is neglected). In our previous papers, the influence of the electron on the muon was taken into account; however, in the rotating frame used in our previous papers, the motion of the muon was only metastable (not truly stable), and furthermore, only circular orbits of the electron were considered in our previous paper. In the present paper, we show that the effective potential energy of the Rydberg electron is mathematically equivalent to the potential energy of a satellite moving around an oblate planet. Based on this, we demonstrate that the unperturbed orbital plane of the Rydberg electron undergoes simultaneously two different precessions: precession within the orbital plane and precession of the orbital plane around the axis of the muonic circular orbit. We provide analytical expressions for the frequencies of both precessions. The shape of the elliptical orbit of the Rydberg electron is not affected by the perturbation, which is the manifestation of the (approximate) conservation of the square of the angular momentum of the Rydberg electron. This means that the above physical systems have a higher than geometrical symmetry (also known as a hidden symmetry) which is a counterintuitive result of general physical interest. We note that the above problem of the motion of the Rydberg electron in muonic-electronic helium atoms or helium-like ions is mathematically equivalent to another problem from atomic physics: a hydrogen Rydberg atom in a linearly-polarized electric field of a high-frequency laser radiation. (author)
[en] Silver nanoparticles (AgNPs) are one of the new cancer treatment tools due to their unique properties that enhance potential therapeutic efficacy. In this study, we describe the extracellular biosynthesis and anticancer activity of AgNPs using the Anabaena flos-aquae biomass extract as reducing agent. The formation of dark-brown AgNO3 /extract solution confirmed the reduction of silver ions into AgNPs. In addition, the ultraviolet–visible spectroscopy showed the surface plasmon peak at 425 nm as characteristic peak for AgNPs. Transmission electron microscopy and scanning electron microscopy showed highly stable and mostly spherical AgNPs with average size of 5–25 nm. Fourier transform infrared spectral analysis confirmed the presence of biomolecules in the extract involved in the reduction and stabilization of AgNPs. In vitro , study of anticancer and cytotoxic effect of AgNPs and extract against T47D cell lines by MTT assay and flow cytometry confirmed the anti-proliferation potential of AgNPs against breast cancer cells. In conclusion, our results revealed that Anabaena can be used as a good organism for biologically synthesis of AgNPs and confirmed the potent therapeutic value of these nanoparticles as anticancer drugs. (author)
[en] A simple theoretical model is developed to calculate the size and shape dependent melting temperature and catalytic activation energy of freestanding and embedded nanoparticles (NPs) using the cohesive energy expressions. In case of freestanding NPs melting temperature is found to decrease with reducing size, while in case of embedded nanoparticles the bonding between the embedded nanoparticles and the matrix affects the melting of Ag/Ni, In/Al and Pb/Al nanoparticles. As a result selected NPs shows superheating in embedded form. In terms of ratio of sequence of Catalytic activation energy for freestanding NPs follows as Ean/E-ab(tetrahedron)> Ean/Eab (octahedron)> Ean/Eab (nanosphere)> Ean/Eab (icosahedron) for constant size. Catalytic activation energy of free and embedded Pt nanoparticles for various shapes and size have been calculated and compared with the experimental data. The model is found consistent with available experimental data in terms of melting and catalytic activation energy of free and embedded nanoparticles
[en] Motivated by recent developments in the experimental study of Bose–Fermi mixtures, we investigate ground-state phase diagrams and excitation spectra for Bose–Fermi mixtures in a three-dimensional (3D) optical lattice. The Gutzwiller approximation is used to identify a new phase in which both superfluid bosons and metal fermions coexist. As a useful probe to identify the quantum phases, we also calculate the excitation spectra. In Mott insulator phase, two excitation features appear in the spectra that correspond to particle and hole excitations. In superfluid phase, there are Bogoliubov modes and amplitude modes. In coexisting phase, two gapless dispersive modes are identified, which shift due to interaction between bosons and fermions. (author)
[en] Li2AMo3O8 (A=In or Sc) is a molecular based spin-1/2 triangular lattice system where spin-1/2 Mo3O13 clusters in place of Mo ions form the uniform triangular lattice. Their ground states are different according to the A site. Li2InMo3O8 undergoes conventional 120deg long-range magnetic order below TN = 12 K whereas isomorphic Li2ScMo3O8 exhibits no long-range magnetic order down to 0.5 K. Here, we report exotic magnetisms in Li2InMo3O8 and Li2ScMo3O8 investigated by inelastic neutron scattering (INS) using polycrystalline samples. Li2InMo3O8 and Li2ScMo3O8 show completely different INS spectra, representing their different ground states. Li2InMo3O8 exhibits spin wave excitation which is quantitatively described by the nearest neighbor anisotropic Heisenberg model based on the 120deg spin structure. In contrast, Li2ScMo3O8 undergoes short-range magnetic order below 4 K with quantum-spin-liquid-like magnetic fluctuations down to the base temperature. Origin of the different ground states is discussed in terms of anisotropies of crystal structures and magnetic interactions. (author)
[en] The explicit expression of the vibrational partition function for the modified Pöschl–Teller plus Woods–Saxon potential has been presented in a closed-form. The analytical expression for the vibrational mean energy have also been calculated were other thermodynamic functions like the vibrational specific heat, free energy, and the entropy for the gallium nitride wurtzite crystal structure have been determined in details. The dependence of these functions on the potential parameters has also been discussed in detail. By using the ground state energy and the probability density, the behaviours of some theoretic quantities (Shannon entropy and Fisher information entropy) have also been calculated and analyzed graphically as a function of the potential parameters. (author)