Magnetooptical properties of a molecular D<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>-ion in a quantum wire

In the framework of a model of zero-range potential, the problem of bound states of an electron in the field of two D0 centers (a two-center problem) in a semiconductor quantum wire is considered in the presence of a longitudinal magnetic field. It is shown that the magnetic field produces a significant shift of g and u terms and stabilizes the D ₂ ^? states in quantum wires. It is found that, in the case of transverse polarization of light, the spectral dependence of the photoionization cross section of a D ₂ ^? center exhibits the quantum-confined Zeeman effect with strongly pronounced oscillations of interference nature.     

Fabrication of a nanoparticle TiO<Subscript>2</Subscript> photoelectrochemical cell utilizing a solid polymeric electrolyte of PAN–PC–LiClO<Subscript>4</Subscript>

A nanoparticle TiO₂ solid-state photoelectrochemical cell utilizing as a solid electrolyte of poly(acrylonitrile)–propylene–carbonate–lithium perchlorate (PAN–PC–LiClO₄) has been fabricated. The performance of the device has been tested in the dark and under illumination of 100-mW cm⁻² light. A nanoparticle TiO₂ film was deposited onto indium tin oxide-covered glass substrate by controlled hydrolysis technique assisted with spin-coating technique. The average grain size for the TiO₂ film is 76 nm. LiClO₄ salt was used as a redox couple. The room temperature conductivity of the electrolyte is 4.2 × 10⁻⁴ S cm⁻¹. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows the rectification property in the dark and shows the photovoltaic effect under illumination. The best J _sc and V _oc of the device were 2.82 μA cm⁻² and V _oc of 0.58 V, respectively, obtained at the conductivity of 4.2 × 10⁻⁴ S cm⁻¹ and intensity of 100 mW cm⁻². The J _sc was improved by about three times by introducing nanoparticle TiO₂ and by using a solid electrolyte of PAN–PC–LiClO₄ replacing PVC–PC–LiClO₄ in the device. The current transport mechanism of the cell is also presented in this paper.     

Can a future choice affect a past measurement’s outcome?

An EPR experiment is studied where each particle within the entangled pair undergoes a few weak measurements (WMs) along some pre-set spin orientations, with the outcomes individually recorded. Then the particle undergoes one strong measurement along an orientation chosen at the last moment. Bell-inequality violation is expected between the two final measurements within each EPR pair. At the same time, statistical agreement is expected between these strong measurements and the earlier weak ones performed on that pair. A contradiction seemingly ensues: (i) Bell’s theorem forbids spin values to exist prior to the choice of the orientation measured; (ii) A weak measurement is not supposed to determine the outcome of a successive strong one; and indeed (iii) Almost no disentanglement is inflicted by the WMs; and yet (iv) The outcomes of weak measurements statistically agree with those of the strong ones, suggesting the existence of pre-determined values, in contradiction with (i). Although the conflict can be solved by mere mitigation of the above restrictions, the most reasonable resolution seems to be that of the Two-State-Vector Formalism (TSVF), namely, that the choice of the experimenter has been encrypted within the weak measurement’s outcomes, even before the experimenters themselves know what their choice will be.     

Single longitudinal mode pulse from a TEA CO<Subscript>2</Subscript> laser by using a three-mirror resonator with a Fabry–Pérot etalon

We present a single longitudinal mode (SLM) TEA CO₂ laser oscillation by using a three-mirror resonator with a Fabry–Pérot etalon. The etalon was inserted in the optical path taken out from the main resonator of the CO₂ laser for protecting the etalon from damage on the surface. A modified numerical model of the three- mirror resonator was investigated for design the laser. SLM pulse from the TEA CO₂ laser was achieved, and the experimentally measure values were found to have good agreement with the numerical model. The maximum pulse energy of reliable SLM emission is obtained in excess of 200 mJ at 9.57 μm. The reliability of producing SLM pulses was higher than 90%, and there was no damage on the etalon PACS  42.55.Lt; 42.60.Fc     

Promising performances for a La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>0.8</Subscript>Fe<Subscript>0.2</Subscript>O<Subscript>3-δ</Subscript> cathode with a dense interfacial layer at the electrode-electrolyte interface

As for the commonly studied La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (6428), here, a very low area-specific resistance (ASR) was measured for La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δ (6482) cathode deposited on a Ce_0.9Gd_0.1O_2-δ (GDC) electrolyte with addition of a thin (1 μm) dense LSCF film deposited by spin coating at the interface between the GDC electrolyte and a 40-μm-thick screen-printed electrode. The ASR ranged from 1 Ω.cm² at 500 °C, 0.11 Ω.cm² at 625 °C and value as low as 0.03 Ω.cm² at 700 °C. Impedance spectra collected in between 500 and 700 °C were carefully studied. They could all be modelled with two R//CPE in series which are likely associated to the oxygen reduction reaction itself (dissociation/adsorption/ionization) at low frequency and to the oxide ion transfer at the electrode/electrolyte interface at high frequency.     

Multiphoton SRS-Lasing in a Monoclinic β-BaYb<Subscript>2</Subscript>F<Subscript>8</Subscript> Crystal

The discovery of stimulated Raman scattering (SRS) in monoclinic fluoride β-BaYb₂F₈ known as a host matrix for Ln³⁺ lasant ions was reported. All the recorded spectral components of Stokes and anti-Stokes χ⁽³⁾-nonlinear picosecond generation were assigned to the three SRS-active photon A_g- and B_g-modes of a crystal (ω_SRS1 ~ 362 cm^–1, ω_SRS2 ~ 295 cm^–1, and ω_SRS3 ~ 230 cm^–1).     

Triple correlations in a A<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>B<Subscript>1 − <Emphasis Type="Italic">y</Emphasis></Subscript> solid solution with a planar hexagonal lattice

It is shown that triple correlations in a A _y B_{1 ? y} solid solution with a planar hexagonal lattice are due to the presence of nearest-pair correlations. The admissible range of the triple correlation as a function of the composition of the A _y B_{1 ? y} solid solution and pair correlation value is determined. It is shown that periodically ordered planar hexagonal and square-island nanostructures can be considered as A_1/4□ _3/4 solid solutions with vacant sites □ and sites occupied by nanoparticles A. In this case, the ordered distribution of the nanoparticles over the sites of the planar lattice is caused by the nearest-air correlation that is negative in sign and maximal in absolute value.     

Cooling of a <Emphasis Type="Italic">Λ</Emphasis>-type three-level atom in a high-finesse optical cavity

A theoretical study is carried out for the cavity cooling of a Λ-type three-level atom in a high-finesse optical cavity driven by a weakly field. Analytical expressions for the friction, diffusion coefficients and the equilibrium temperature are obtained by using the Heisenberg equations, then they are calculated numerically and shown graphically as functions of the controlling parameters. For a suitable choice of these parameters, the dynamics of the cavity field interaction with the Λ-type three-level atom introduces a sisyphus cooling mechanism yielding lower temperature than the one of the two-level atom, avoiding the problems induced by spontaneous emission.     

Search for a Neutrino with a Mass of 0.01–1.0 MeV in Beta Decays of <Superscript>144</Superscript>Ce–<Superscript>144</Superscript>Pr Nuclei

Spectra of electrons from beta decays of ¹⁴⁴Ce–¹⁴⁴Pr nuclei have been measured and analyzed in order to find a contribution from a heavy neutrino. For the neutrino with the mass m_νH in the interval of 150–350 keV, a new upper bound |U_eH|² ≤ (2?5) × 10^?3 at 90% C.L. has been found for the mixing parameter.     

Concept of a demonstrational hybrid reactor—a tokamak with molten-salt blanket for <Superscript>233</Superscript>U fuel production: 1. Concept of a stationary Tokamak as a neutron source

On the basis of current understanding of physical processes in tokamaks and taking into account engineering constraints, it is shown that a low-cost facility of a moderate size can be designed within the adopted concept. This facility makes it possible to achieve the power density of neutron flux which is of interest, in particular, for solving the problem of ²³³U fuel production from thorium. By using a molten-salt blanket, the important task of ensuring the safe operation of such a reactor in the case of possible coolant loss is accomplished. Moreover, in a hybrid reactor with the blanket based on liquid salts, the problem of periodic refueling that is difficult to perform in solid blankets can be solved.     

Composition-induced transition of spin-modulated structure into a uniform antiferromagnetic state in a Bi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript>x</Subscript>FeO<Subscript>3</Subscript> system studied using <Superscript>57</Superscript>Fe NMR

By analyzing the NMR line shape, the transformation of a spatially spin-modulated magnetic structure in BiFeO₃ into an ordinary spatially uniform structure of the LaFeO₃ orthoferrite in Bi_1?xLa_xFeO₃ solid solutions is studied. The measurements are made using a spin-echo technique at temperatures of 77 and 4.2 K on ceramics with compositions x=0, 0.1, 0.2, 0.61, 0.9, and 1.0 enriched by the ⁵⁷Fe isotope. It is shown that the spin-modulated structure disappears near the concentration x=0.2, which corresponds, according to the published data, to the phase transition with a change in the unit-cell symmetry R3c → C222. A formula is obtained describing the NMR absorption line shape for the spin-modulated structure with account of local line-width. Theoretical spectra adequately describe the evolution of the experimental spectrum in the concentration range 0≤x≤0.2. Highly nonuniform local magnetic fields in the intermediate compositions make it impossible to detect NMR signals in a sample with x=0.61. A uniform magnetic structure characterized by a single narrow line arises in the range of existence of a phase with the symmetry Pnma typical of the pure orthoferrite LaFeO₃.     

Spectroscopy of the <Stack><Subscript>Λ</Subscript><Superscript>7</Superscript></Stack>He nucleus in a three-cluster model

The _Λ ⁷ He hypernucleus is considered within the _Λ ⁵ He + n + n cluster model. The hyperon—nucleon interaction is described by a one-boson-exchange potential that is constructed on the basis of the NSC97f model. Phenomenological potentials are used to describe the αΛ and αN interactions. For the _Λ ⁵ Hen interaction, use is made of the folding-model potential. The calculations of the hyperon binding energy in the ground state of the _Λ ⁷ He hypernucleus on the basis of Faddeev equations in configuration space yield a result (5.35 MeV) that agrees well with preliminary experimental data (5.4 MeV). The problem of calculating the hyperon binding energy within the three-body approach is discussed. In calculating the energy spectrum of _Λ ⁷ He, use is made of a version of the method of analytic continuation in the coupling constant. Low-lying excited states of this nucleus can be classified as an analog of the corresponding states of the ⁶He nucleus with allowance for the clustering of the _Λ ⁵ He+n+n system in the ⁶He(J ^π)+Λ(s) form.     

LiNbO<Subscript>3</Subscript>–Yb<Superscript>3+</Superscript> crystal as a material for optical temperature sensor

The method of optical determination of temperature based on cooperative luminescence in the LiNbO₃ crystals doped with rare earth ions is proposed. As a temperature-dependent measurable characteristic, the quantum yield of luminescence is considered taking into account the processes of nonradiative redistribution of the electron excitation energy in the impurity subsystem. It is shown that the LiNbO₃–Yb³⁺ crystals can be used as a material for optical temperature sensors in the temperature range of 200–500 K with the average sensitivity of 0.12%K^–1.     

Mössbauer study of mechanical alloying in a Mo<Subscript>80</Subscript>Fe<Subscript>20</Subscript> system

The sequence of solid state reactions upon the mechanical alloying of Mo and Fe powders with an 80: 20 atomic ratio was established by means of Mössbauer spectroscopy and X-ray diffraction. At the first stage, a nanostructure and Mo₆₃Fe₃₇ hexagonal close packed (HCP) phase are formed in Mo body-centered cubic lattice (BCC) particles. At the second stage, a body-centered cubic lattice of Mo-Fe solid solution is formed. The process is accompanied by the formation of a minor amount (about 20%) of X-ray amorphous phase.     

Current dependent fluctuations in a Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>CuO<Subscript>6+δ</Subscript> thin film

The current dependence of the excess conductivity is measured up to ≃3T_c for a Bi₂Sr₂CuO_6+δ thin film, as a function of doping. It is found to be anomalously sensitive to the transport current and to behave as a universal function of T/T_c in the whole doping range. We discuss these results in the perspective of a granular superconductor with a gapless-like behavior.     

Detection of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−x</Subscript> magnetization nonlinearity in a pseudogap region

The temperature dependences of magnetization higher harmonics were studied experimentally in single-domain YBa₂Cu₃O_7?x samples above T _c . YBa₂Cu₃O_7?x magnetization nonlinearity was found in different samples up to temperatures T = 103–112 K, which is much higher than the temperature of transition into the superconducting state of the given compound. The observed specific feature of YBa₂Cu₃O_7?x magnetization is associated with the occurrence of pseudogap state in this compound.     

Synthesis and Photoluminescence Behavior of the Eu<Superscript>3+</Superscript> Ions as a Nanocoating over a Silica Stöber Matrix

In this work, a SiO₂ spherical were prepared by the Stöber Method and then recovered with a single layer of Eu₂O₃ oxide (SiO₂@Eu₂O₃) obtained by the Polymeric Precursor Method. The SiO₂@Eu₂O₃ powder was heated treated at 100, 300, 400, 500 and 800 °C. The samples were characterized by the Scanning Electonic Microscopy (SEM), Thermal Analysis (TGA/DTA), and the luminescent properties of the SiO₂@Eu₂O₃ powders were studied by their emission and excitation spectra as well as by the lifetime measurements of the Eu^{3+ 5}D₀?→?⁷F₂ transition. The SEM analysis shows that the silica prepared by the Stöber Method is spherical with a particle size of 460 nm. The emission spectra of the SiO₂@Eu₂O₃ powders presented the Eu³⁺ characteristics bands related to the ⁵D₀?→?⁷F_J (J?=?0, 1, 2, 3, 4) transitions at 577, 591, 616, 649 and 695 nm, respectively. The band related to the ⁵D₀?→?⁷F₂ transition is the most intense in the spectra, and its intensity decreases with the temperature enhancement. The decay curves of the SiO₂@Eu₂O₃ samples presented monoexponential features, and the obtained lifetime values were higher than the Eu₂O₃ oxide. It was possible to conclude that the ⁵D₀?→?⁷F₂ hypersensitive transition is strongly dependent on the Eu³⁺ surrounding.     

Emission of Cu<Subscript>2</Subscript>O Paraexcitons Confined by a Strain Trap: Hints of a Bose–Einstein Condensate?

We monitor the phonon sideband emission from paraexcitons confined in a strain trap in cuprous oxide at T = 1.25 K. On the low energy ank of the optical phonon replicas, both of Γ ₅ ^? and Γ ₃ ^? symmetry (the latter activated by application of a magnetic field), we detect sharp peaks that might represent indications for a paraexciton Bose–Einstein condensate. In contrast, such peaks are absent in the phonon-mediated emission of the orthoexcitons, and they also disappear at elevated temperatures. The results challenge our understanding of the involved physics, e.g., of the Auger recombination of excitons, which has so far been believed to prevent crossing the border to a condensate.     

Steady state mode-locking of a 1.34 μm Nd:YVO<Subscript>4</Subscript> laser using a single-walled carbon nanotube saturable absorber

Steady state mode-locked operation of a neodymium laser operating on the ⁴F_3/2 → ⁴I_13/2 transition around 1.3 μm is achieved for the first time using transmitting single-walled carbon nanotube (SWCNT) saturable absorber. The Nd:YVO₄ laser cavity was optimized for large fundamental mode volume generating an average power of 0.8 W at a repetition rate of 127 MHz in a stable train of 16.5 ps long pulses.