Combined effects of electric field and hydrostatic pressure on electron states in asymmetric GaAs/(Ga,Al) triple quantum dots

The combined effects of an in-growth direction applied electric field and hydrostatic pressure on the exciton binding energy and photoluminescence energy transitions are reported in this work for triple vertically coupled quantum dots. The calculations have been carried out within the effective mass approximation, and using a variational procedure. The results show that the exciton binding energy and the photoluminescence energy transitions are functions of external probes like the hydrostatic pressure and the applied electric field.     

Characterization of UO 2 2+ exchanged Y zeolite

The present study discusses the incorporation of uranyl ion into Y-zeolite framework. The UO ₂ ²⁺ sorption was measured by neutron activation analyses. The Y-zeolite framework distorts in response to the cations present in the structure. Hence, depending on the amount and the location of the exchanged cations, the features of the X-ray diffraction pattern may vary. From the Rietveld analysis of these patterns, the positions occupied by the UO ₂ ²⁺ cations in the zeolite network were determined.     

Water-dispersible sugar-coated iron oxide nanoparticles. An evaluation of their relaxometric and magnetic hyperthermia properties

Synthesis of functionalized magnetic nanoparticles (NPs) for biomedical applications represents a current challenge. In this paper we present the synthesis and characterization of water-dispersible sugar-coated iron oxide NPs specifically designed as magnetic fluid hyperthermia heat mediators and negative contrast agents for magnetic resonance imaging. In particular, the influence of the inorganic core size was investigated. To this end, iron oxide NPs with average size in the range of 4-35 nm were prepared by thermal decomposition of molecular precursors and then coated with organic ligands bearing a phosphonate group on one side and rhamnose, mannose, or ribose moieties on the other side. In this way a strong anchorage of the organic ligand on the inorganic surface was simply realized by ligand exchange, due to covalent bonding between the Fe(3+) atom and the phosphonate group. These synthesized nanoobjects can be fully dispersed in water forming colloids that are stable over very long periods. Mannose, ribose, and rhamnose were chosen to test the versatility of the method and also because these carbohydrates, in particular rhamnose, which is a substrate of skin lectin, confer targeting properties to the nanosystems. The magnetic, hyperthermal, and relaxometric properties of all the synthesized samples were investigated. Iron oxide NPs of ca. 16-18 nm were found to represent an efficient bifunctional targeting system for theranostic applications, as they have very good transverse relaxivity (three times larger than the best currently available commercial products) and large heat release upon application of radio frequency (RF) electromagnetic radiation with amplitude and frequency close to the human tolerance limit. The results have been rationalized on the basis of the magnetic properties of the investigated samples.     

Γ-X mixing in GaAs-Ga<Subscript>1-x</Subscript>Al<Subscript>x</Subscript>As quantum wells under hydrostatic pressure

The mixing between the Γ and X conduction-band valleys in GaAs-Ga_1-xAl_xAs quantum wells is investigated by using a phenomenological model which takes into account the effects of applied hydrostatic pressure. The dependencies of the variationally calculated photoluminescence peak-energy transitions on the applied hydrostatic pressure and quantum-well width are presented. A systematic study of the Γ-X mixing parameter is also reported. In particular, it is shown that the inclusion of the Γ-X mixing explains the non-linear behavior in the photoluminescence peak of confined exciton states that has been experimentally observed for pressures above 15 kbar in GaAs-Ga_1-xAl_xAs quantum wells.     

Structural and magnetic properties of nanocrystalline particles in an amorphous Fe73.5Nb3CuSi13.5B9 matrix

We report structural and magnetic properties of fine particles embedded in an amorphous magnetic matrix. As-quenched amorphous Fe_73.5Nb₃CuSi_13.5B₉ ribbons (FINEMET) were submitted to the thermal treatments of several times (1 ? t ? 240 min) at 570 °C using a conventional furnace. The analyses of the X-ray diffraction patterns at room temperature reveal that our samples consist of single phase Fe₃Si nanocrystals embedded in a residual amorphous phase. Magnetic measurements show that the saturation moment at T = 450 °C increases as a function of annealing time. This behavior is attributed to an increase of the fraction of nanocrystallites in the residual amorphous phase.     

Non-crossing monotone paths and binary trees in edge-ordered complete geometric graphs

Acta Mathematica Hungarica - This paper is devoted to the studying of the weak Orlicz–Lorentz space $$\Lambda_X^{\varphi, \infty}(w)$$ , which can be regarded as an extension of weak Orlicz...     

C-24 stereochemistry of marine sterols: (22E)-24-(isopropenyl)-22-dehydrocholesterol and 24-isopropenylcholesterol

The C-24 configuration of (22E,24xi)-24-isopropenyl-22-dehydrocholesterol (1), which was recently isolated from the Colombian Caribbean sponge, Topsentia ophiraphidites, was investigated. Synthesis of the stereodefined (24R)- and (24S)-(22E)-24-isopropenyl-22-dehydrocholesterols (1a, 1b) followed by (1)H- and (13)C-NMR data comparison of these sterols established the (24R)-configuration of 1. In addition, (24R)- and (24S)-24-isopropenylcholesterols (2a and 2b) were also synthesized and their NMR data are provided. The C-24 configurations of the samples of 24-isopropenylcholesterol reported previously are discussed.     

Optical Absorption in Periodic Graphene Superlattices: Perpendicular Applied Magnetic Field and Temperature Effects

A detailed study of the magneto‐optical absorption is presented for graphene superlattices (SLs) subjected to a perpendicular magnetic field. For a given temperature, this quantity exhibits a resonant peak structure whose characteristics depend on the magnetic field regime, circular polarization of light and SL barrier height. For the intermediate field regime, we demonstrated that the resonant peak structure of is directly correlated to the partial joint density of states. Specifically, the latter exhibits van Hove‐like singularities and peaks at energies where takes its maximum values. We also investigated the magnetoabsorption in the weak field regime for SLs exhibiting one and extra Dirac points in the absence of the field. It was found that for SLs with only one Dirac point, the absorption spectra consist of resonant peaks satisfying the same circular polarization dependent selection rule as that for pristine graphene, except for one of them. For SLs with extra Dirac points, the resonant peaks arise from transitions between singlet subbands or between doublet subbands and satisfy a circular polarization and peak intensity dependent selection rule. It was also found that the resonant structure of can be observed experimentally at room temperature in clean SLs.     

Quantum interference between the third and fourth exciton states in semiconducting carbon nanotubes using resonance Raman spectroscopy

We exploit an energy level crossover effect [Haroz et al., Phys. Rev. B 77, 125405 (2008)] to probe quantum interference in the resonance Raman response from carbon nanotube samples highly enriched in the single semiconducting chiralities of (8,6), (9,4), and (10,5). UV Raman excitation profiles of G-band spectra reveal unambiguous signatures of interference between the third and fourth excitonic states (E(33) and E(44)). Both constructive and destructive responses are observed and lead to anomalous intensity ratios in the LO and TO modes. Especially large anomalies for the (10,5) structure result from nearly identical energies found for the two E(ii) transitions. The interference patterns demonstrate that the sign of the exciton-phonon coupling matrix elements changes for the LO mode between the two electronic states, and remains the same for the TO mode. Significant non-Condon contributions to the Raman response are also found.