Transparent colloid containing upconverting nanocrystals: An alternative medium for three-dimensional volumetric display

We report an alternative medium of transparent upconverting colloid containing lanthanide ion doped NaYF4 nanocrystals for three-dimensional (3D) volumetric display. The colloids exhibit tunable upconversion luminescence with a wide spectrum of colors by adjusting the doping concentrations of the nanocrystals and the compositions of the colloids. Our preliminary experimental result indicates that an upconverting colloid-based 3D volumetric display using a convergent, near infrared laser beam to induce a localized luminescent spot near the focus is technically feasible. Therefore arbitrary 3D objects can be created inside the upconverting colloid by use of computer controlled 3D scanning systems. (C) 2008 Optical Society of America

Three-dimensional micro- and nano-fabrication in transparent materials by femtosecond laser

Femtosecond pulsed lasers have been widely used for materials microprocessing. Due to their ultrashort pulse width and ultrahigh light intensity, the process is generally characterized by the nonthermal diffusion process. We observed various induced microstructures such as refractive-index-changed structures, color center defects, microvoids and microcracks in transparent materials (e.g., glasses after the femtosecond laser irradiation), and discussed the possible applications of the microstructures in the fabrication of various micro optical devices [e.g., optical waveguides, microgratings, microlenses, fiber attenuators, and three-dimensional (3D) optical memory]. In this paper, we review our recent research developments on single femtosecond-laser-induced nanostructures. We introduce the space-selective valence state manipulation of active ions, precipitation and control of metal nanoparticles and light polarization-dependent permanent nanostructures, and discuss the mechanisms and possible applications of the observed phenomena.

Protein three-dimensional structural databases: Domains, structurally aligned homologues and superfamilies

This paper reports the availability of a database of protein structural domains (DDBASE), an alignment database of homologous proteins (HOMSTRAD) and a database of structurally aligned superfamilies (CAMPASS) on the World Wide Web (WWW). DDBASE contains information on the organization of structural domains and their boundaries; it includes only one representative domain from each of the homologous families. This database has been derived by identifying the presence of structural domains in proteins on the basis of inter-secondary structural distances using the program DIAL [Sowdhamini & Blundell (1995), Protein Sci. 4, 506-520]. The alignment of proteins in superfamilies has been performed on the basis of the structural features and relationships of individual residues using the program COMPARER [Sali & Blundell (1990), J. Mol. Biol. 212, 403-428]. The alignment databases contain information on the conserved structural features in homologous proteins and those belonging to superfamilies. Available data include the sequence alignments in structure-annotated formats and the provision for viewing superposed structures of proteins using a graphical interface. Such information, which is freely accessible on the WWW, should be of value to crystallographers in the comparison of newly determined protein structures with previously identified protein domains or existing families.

The three dimensional structure and biological domains of the p53 C-terminus.

It was expected that there are a coil (289 similar to 325) and two a helix (alpha(1)368 similar to 373, alpha(2)381 similar to 388) structures in p53 protein C-terminal region based on its mRNA secondary structure template and Chou-Fasman's protein secondary structure principle of prediction. The result was conformed by the other four methods of protein secondary structure prediction that are based on the multiple sequence alignment (accuracy = 73.20%). Combine with the 31 amino acids crystal structure of the oligomerization, the three dimensional conformation of p53 C-terminal 108 residues was built using the SGI INDIGO(2) computer. This structure further expounds the relationship among those biological function domains of p53 C- terminus at three-dimensional level.

Is there a genetic relationship between mRNA and the encoded protein at three-dimensional level?

A comparative study on the structures of some mRNAs and their encoded proteins shows an intriguing correlation between the two foldings. Non-random distribution of codons in the secondary structures of mRNAs is also shown, which appears to be in accordance with the conformational properties of amino acids in protein structures to some extent. These results seem to suggest that there may be a kind of genetic relationship between mRNA and protein at three-dimensional level.

Rashba electron transport in one-dimensional quantum waveguides

The properties of Rashba wave function in the planar one-dimensional waveguide are studied, and the following results are obtained. Due to the Rashba effect, the plane waves of electron with the energy E divide into two kinds of waves with the wave vectors k(1)=k(0)+k(delta) and k(2)=k(0)-k(delta), where k(delta) is proportional to the Rashba coefficient, and their spin orientations are +pi/2 (spin up) and -pi/2 (spin down) with respect to the circuit, respectively. If there is gate or ferromagnetic contact in the circuit, the Rashba wave function becomes standing wave form exp(+/- ik(delta)l)sin[k(0)(l-L)], where L is the position coordinate of the gate or contact. Unlike the electron without considering the spin, the phase of the Rashba plane or standing wave function depends on the direction angle theta of the circuit. The travel velocity of the Rashba waves with the wave vector k(1) or k(2) are the same hk(0)/m*. The boundary conditions of the Rashba wave functions at the intersection of circuits are given from the continuity of wave functions and the conservation of current density. Using the boundary conditions of Rashba wave functions we study the transmission and reflection probabilities of Rashba electron moving in several structures, and find the interference effects of the two Rashba waves with different wave vectors caused by ferromagnetic contact or the gate. Lastly we derive the general theory of multiple branches structure. The theory can be used to design various spin polarized devices.

STUDY ON MICROWAVE CYCLOTRON RESONANCE OF HIGH-MOBILITY GaAs/Al-0.35 Ga-0.65 As TWO-DIMENSIONAL ELECTRON GAS

The properties of electron states in the presence of microwave irradiation play a key role in understanding the oscillations of longitudinal resistance and the zero-resistance states in a high-mobility two-dimensional electron gas(2DEG) in low magnetic field. The properties of electron states in a high-mobility and low-density GaAs/Al0.35Ga0.65As 2DEG in the presence of Ka-band microwave irradiation were studied by reflectance-based optically detected cyclotron resonance(RODCR). The influences of the direction of microwave alternating electronic field, wavelength of the laser, and temperature on RODCR results were discussed. The results show that RODCR measurements provide a convenient and powerful method for studying electron states in 2DEG.

Design of novel polarization beam splitter in two-dimensional photonic crystal

We present the design and the simulation of an ultracompact high efficiency polarization beam splitter (PBS) based on the properties of the light waves propagating in straight waveguide and composite structure photonic crystal. The splitting properties of the PBS are numerically simulated and analyzed by using the plane wave expansion (PWE) method and finite difference time domain (FDTD) method. The PBS consists of three parts, namely, input waveguide, beam structure and output waveguide. It is shown that a high efficiency and a large separating angle for TE mode and TM mode can be achieved. Owing to these excellent features, including small size and high rate, the PBS makes a promising candidate in the future photonic integrated circuits.

Quantum efficiency of GaAs/AlGaAs thin films with two-dimensional photonic crystals

The optical properties of GaAs/AlGaAs thin films with photonic crystals were investigated by measuring their photoluminescence spectra. The spectral intensities, lifetimes, and quantum efficiencies decreased greatly compared with those in blank material without photonic crystals. The quantum efficiencies in the material were also calculated from spectral intensities and lifetimes and the quantum efficiencies calculated from those two methods agreed with each other to some extent.

Anomalous photogalvanic effect of circularly polarized light incident on the two-dimensional electron gas in AlxGa1-xN/GaN heterostructures at room temperature

Under normal incidence of circularly polarized light at room temperature, a charge current with swirly distribution has been observed in the two-dimensional electron gas in Al0.25Ga0.75N/GaN heterostructures. We believe that this anomalous charge current is produced by a radial spin current via the reciprocal spin Hall effect. It suggests a new way to research the reciprocal spin Hall effect and spin current on the macroscopic scale and at room temperature.

The impact of imperfect symmetry on band edge modes of a two-dimensional photonic crystal with square lattice

A theoretical analysis has been performed by means of the plane-wave expansion method to examine the dispersion properties of photons at high symmetry points of an InP based two-dimensional photonic crystal with square lattice. The Q factors are compared qualitatively. The mechanism of surface-emitting is due to the photon manipulation by periodic dielectric materials in terms of Bragg diffraction. A surface-emitting photonic crystal resonator is designed based on the phenomenon of slow light. Photonic crystal slabs with different unit cells are utilized in the simulation. The results indicate that the change of the air holes can affect the polarization property of the modes. So we can find a way to improve the polarization by reducing the symmetry of the structure.