Laser-induced quantum adsorption of neutral atoms in dielectric surfaces

We propose an optical technique to load neutral atoms in quantum adsorption states of a dielectric surface. Considering a realistic atom–surface potential well, we show that free cold lithium atoms approaching a LiF surface may be transferred to a surface bound state of the first excited atomic state. We also discuss schemes to populate adsorption energy levels of the atomic electronic ground state, and we find that spontaneous mechanisms transfer more than 90% of the excited adsorbed atoms into vibrational levels of the fundamental adsorption potential. The lifetime of the resulting two-dimensional waveguide is calculated, considering the adatoms’ interaction with the crystal phonons. PACS 34.50.Dy; 68.43.-h; 68.35.Ja; 32.80.Pj     

Electrostatic surface shape resonances of a finite number of ridges

The resonance properties of localized electrostatic surface modes associated with a finite number of ridges on an otherwise planar surface are investigated. Numerical solutions of the homogeneous integral equations that describe the electromagnetic fields in the vicinity of the ridges are used to obtain the dispersion relation of surface plasmons. The frequencies of the electrostatic surface shape resonances are calculated for ridges with Gaussian, Lorentzian, sinusoidal, exponential, and triangular profiles. We show the existence of splittings of the plasmon frequencies, which depends on the surface profile function and on the distance between the ridges. Considering the ridge with a sinusoidal profile, we obtain the limit on the number of ridges which generates a frequency splitting of the electrostatic surface shape resonances, whose frequency values converge to those of the dispersion relation of surface plasmons on one-dimensional sinusoidal grating. Received: 24 June 1997 / Received in final form: 5 September 1997 / Accepted: 15 September 1997     

Degenerate Landau levels for tripod-type cold atoms in U(2) Abelian gauge field

New data for positronium beam production efficiency are presented. As a converter of positrons to forward-going positronium, O₂ has been found to be as good as CO₂ from ～250 to 400 eV. Preliminary data is also presented for the production efficiency from Ar at 2.8 eV.     

Surface plasmons on a quasiperiodic grating

A method is presented for calculating the frequencies of non-retarded surface plasmons propagating on a semi-infinite medium with a surface profile described by a one-dimension quasiperiodic function. The profiles are generated, in analogy with previous work on quasiperiodic superlattices, by repeating unitary cells constructed according to an inflation rule. Dispersion relations are obtained for a semi-infinite free-electron metal as the active medium, with surface profiles obeying the Fibonacci and Thue-Morse sequences.Received: 24 June 2003, Published online: 19 November 2003PACS: 73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations) - 71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons     

Synthesis and evaluation of the potential deleterious effects of ZnO nanomaterials (nanoneedles and nanoflowers) on blood components,including albumin,erythrocytes and human isolated primary neutrophils

The application of zinc oxide (ZnO) nanoparticles in biomaterials has increased significantly in the recent years. Here, we aimed to study the potential deleterious effects of ZnO on blood components, including human serum albumin (HSA), erythrocytes and human isolated primary neutrophils. To test the influence of the morphology of the nanomaterials, ZnO nanoneedles (ZnO-nn) and nanoflowers (ZnO-nf) were synthesized. The zeta potential and mean size of ZnO-nf and ZnO-nn suspensions in phosphate-buffered saline were ?10.73 mV and 3.81 nm and ?5.27 mV and 18.26 nm, respectively. The incubation of ZnO with HSA did not cause its denaturation as verified by the absence of significant alterations in the intrinsic and extrinsic fluorescence and in the circular dichroism spectrum of the protein. The capacity of HSA as a drug carrier was not affected as verified by employing site I and II fluorescent markers. Neither type of ZnO was able to provoke the activation of neutrophils, as verified by lucigenin- and luminol-dependent chemiluminescence and by the extracellular release of hydrogen peroxide. ZnO-nf, but not ZnO-nn, induced the haemolysis of erythrocytes. In conclusion, our results reinforce the concept that ZnO nanomaterials are relatively safe for usage in biomaterials. A potential exception is the capacity of ZnO-nf to promote the lysis of erythrocytes, a discovery that shows the importance of the morphology in the toxicity of nanoparticles.     

Bidder's organ of Bufo ictericus: a light and electron microscopy analysis

Male toads of the Bufonidae Family have rudimentary ovaries designated Bidder's organs, and if the testes are removed this organ develops into a functional ovary, representing a morphological strategy for the reproduction of the species. The Bidder's organ of Bufo ictericus was examined using routine and histochemical techniques by light microscopy and transmission electron microscopy. Each Bidder's organ presented a typical ovarian morphology, being composed of a cortex and a medulla. Bidderian follicles in different stages of development were visualized in the cortex, where they are better developed. The germ cells exhibit a large oocyte with a round-shaped nucleus. The Bidderian follicles are supported by a loose net of reticular fibers. In the medullar region, collagen fibers were immersed in the matrix rich in blood vessels that also contained a small quantity of neutral glycoproteins rich in hexose and/or sialic acid and carboxylated polymers with a characteristic distribution of glycosaminoglycans. The oocyte and the follicular cells were separated by a narrow space containing microvilli. The oocyte exhibit a well developed smooth endoplasmic reticulum, a poorly developed Golgi apparatus, and occasional lysosomes. Concentric cisternal complexes are often visualized; however, their morphological significance remains unclear. The peroxisomes display a fine granular matrix without a crystalline core, with a weak 3,3′-diaminobenzidine-reaction. Intimate association between peroxisomes, peroxisomes and lipid inclusions was observed in the oocyte, suggesting its participation in yolk metabolism.     

Transport properties of a 2DEG in the presence of tilted magnetic field: the influence of a 1D modulation

The effect of 1D periodic modulation on the transport and thermodynamic properties of a non-interacting two-dimensional electron gas (2DEG) is investigated. The Hamiltonian used also includes a tilted magnetic field, Rashba, and Dresselhauss spin-orbit interactions. The 1D periodic modulation introduces non-quantized regions on Hall conductivity and a non-zero diffusive conductivity. A method to estimate the modulation periodicity is given using the periodicity of Weiss oscillations on the diffusive conductivity.     

The piecewise linear optimization polytope: new inequalities and intersection with semi-continuous constraints

We give new facets and valid inequalities for the separable piecewise linear optimization (SPLO) knapsack polytope. We also extend the inequalities to the case in which some of the variables are semi-continuous. Finally, we give computational results that demonstrate their efficiency in solving difficult instances of SPLO and SPLO with semi-continuous constraints.