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This paper reviews recent progress in perfect absorbers of electromagnetic waves that utilize metamaterials (MMs). Various numerical techniques that are inevitable for the research on MMs, along with their pros and cons, are commented on and discussed. Abandoning the conventional periodic-boundary conditions is crucial for understanding the discrepancy between simulation and experiments for certain MMs. Broadband perfect absorption can be realized by using multiple resonances and/or multiple units with different sizes in a unit cell, or by utilizing bad Q-factors by incorporating the electrically resistive components, in addition to the ordinary metallic elements. The classical analogue of electromagnetically-induced transparency can be utilized to realize perfect absorption, by employing either structural asymmetry, or near-field interactions. Perspectives and suggestions for further study are discussed. [ABSTRACT FROM AUTHOR]

An optical loss of GaN-based blue-violet laser diodes (BV-LDs) was measured by taking the intensity decay of edge emitting luminescence with respect to the distance from cleaved edge of a wafer to the position where an excitation laser was focused. Amplified spontaneous emission (ASE) was also investigated by tuning the power of an excitation laser on BV-LD wafers. Measurements were performed on wafers with different thicknesses of InGaN optical confinement layers (OCLs). The threshold power of ASE intensity was minimized at an optimum thickness of InGaN OCL. We also found that optical loss of wafers was determined by absorption of an InGaN layer in thicker OCL structure. From experimental data and fittings, we obtained 40 cm-1 for InGaN absorption at 405 nm. The optical field confined in OCL region was reasonably high enough to affect the overall modal loss in devices. Therefore, the optical losses still remained even though the Mg-doped GaN regions are far enough from the active layers. The crystal quality of an InGaN layer should be an important aspect to improve the performance of BV-LDs. [ABSTRACT FROM AUTHOR]

Comparative analysis of optical characteristics of In0.08Ga0.92N/In0.03Ga0.97N multiquantum well (MQW) laser diode structures grown on freestanding GaN and on sapphire substrates is reported. Higher quantum efficiency, higher thermal activation energy, smaller Stokes-like shift, and shorter radiative lifetime are observed for InGaN MQWs on GaN substrate than those of the same MQWs on sapphire substrate. From time-resolved optical analysis, we find that not only an increase in nonradiative lifetime due to reduced dislocation density but also a decrease in radiative lifetime caused by suppressed piezoelectric field play an important role in enhancing optical properties of InGaN MQWs on GaN substrates. [ABSTRACT FROM AUTHOR]

Photoreflectance (PR) spectra at various temperatures and photoluminescence (PL) spectra and high-resolution x-ray rocking curve (XRC) measurements are used to investigate the band alignment, epitaxial-strain, and atomic-ordering effects in In0.54Ga0.46P1-yNy/GaAs (y=0%–2.0%) heterostructures. The existence of additional peaks in PR spectra at higher levels of nitrogen (N) incorporation implies that the band alignment switches from type I to type II, due to the lowering of the conduction band. The electric field at the interface is determined and is discussed with the N content. Redshifts of the PR and PL peaks indicate that the band gap of InGaPN is dramatically reduced as N is incorporated. The valence-band splitting (VBS) and the spin-orbit splitting of InGaPN are obtained from PR spectra. High-resolution XRC measurements indicate that as the N content increases, the lattice mismatch and the compressive strain between the epilayer and GaAs substrate decrease while the VBS increases, which implies an increase in the degree of ordering in InGaPN caused by the transition from a cubic zinc blende structure to a [111] CuPt structure. The order parameter η of InGaPN deduced from the VBS ranges from 0.256 to 0.498, indicating that the InGaPN epilayer becomes more ordered with increasing N incorporation. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of nanoelectromagnets and the magnetic capture of a single magnetic nanoparticle. The magnetic nanoparticles are extracted from magnetotactic bacteria and their diameter is approximately 50 nm. We show that a single nanoparticle is captured at each corner of the serpentine-shaped nanoelectromagnet, and the maximum magnetic field of 35 mT (and the maximum magnetic-field gradient of 4×105 T/m) is shown to be created at the capture spots of the nanoelectromagnet. It is also shown that there is a crossover between the magnetic force and the diffusion force at several hundred nm away from the magnet. This distance is comparable to the average interparticle distance. [ABSTRACT FROM AUTHOR]

Photoreflectance (PR) and Raman spectra were employed to investigate the interfacial characteristics of a series of oxide films on GaAs. The barrier heights across the interfaces and the densities of interracial states are determined from the PR intensity as a function of the pump power density. The oxide-GaAs structures fabricated by in situ molecular beam epitaxy exhibit low interfacial state densities in the low 10[sup 11] cm[sup -2] range. The density of the interface states of the Ga[sub 2]O[sub 3](Gd[sub 2]O[sub 3])-GaAs structure is as low as (1.24±0.14)×10[sup 10] cm[sup -2]. The Ga[sub 2]O[sub 3](Gd[sub 2]O[sub 3]) dielectric film has effectively passivated the GaAs surface. Additionally, Raman spectra were used to characterize the structural properties of the oxide films. [ABSTRACT FROM AUTHOR]

The surface barrier height and surface Fermi level of InA1As were investigated via photoreflectance spectra. Surface state density was then determined from the surface barrier height as a function of temperature, illumination power intensity, and intrinsic layer thickness. Results obtained from these three independent approaches all give the same conclusion, that the surface states are distributed over two separate regions within the energy band gap. Closely examining the photovoltage induced by various incident beam intensities revealed that the photovoltage effect is negligible when the illumination power intensity is below 1.0 µW/cm². [ABSTRACT FROM AUTHOR]

Photoreflectance is used to investigate the band gap, built-in electric field, and surface Fermi level of a series of lattice-matched In[sub 0.52]Al[sub 0.48]As surface-intrinsic n[sup +] structures having different undoped layer thicknesses. Experimental results indicate that, although the built-in electric field depends on the undoped layer thickness, there is a range of thickness within which the surface Fermi level is weakly pinned. From the dependence of electric field and surface Fermi level on the undoped layer thickness, we can determine that the surface states distribute over two separate regions within the energy band gap. The densities of the surface states are evaluated as well. Moreover, the dependence of the built-in electric field on undoped layer thickness is converted into the dependence of surface state density on the surface Fermi level in order to theoretically and exactly calculate the energy spectrum of the surface state density using a Guassian distribution function. The center and width of the distribution near the conduction band are obtained from the fitting parameters. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper presents a Petri-net (PN)-based hierarchical structure for AS/RS operation modelling. The complete AS/RS operation is modelled by four different layer modules, including the command typing layer (CTL), the command profile layer (CPL), the command compilation layer (CCL) and the command execution layer (CEL). To simplify the structure, macro-places are created to represent complicated activities associated with some specific groups of functions. The complete modelling system is implemented in a compact 'Visual C'-based object-oriented computer program. The 'click' function is introduced to allow macro-places to be zoomed in for detailed internal activity visualization. In a typical AS/RS, operation commands are generated and issued by the management system. Each command is first typed and queued in the CTL module and then delivered one by one to the CPL module for work-domain (i.e. the starting and ending locations of the crane) evaluation. After the work-domain is decided, the information is delivered to the CCL module for command sequence compilation. The compiled command sequence is then executed in the CEL module by the crane device. By employing the proposed four-layer modelling procedure, basic AS/RS operation modules of any size can be developed and then assembled to construct a complete AS/RS-PN model. By carefully analysing the properties of the complete AS/RS-PN model, the robustness of the AS/RS structure is verified. [ABSTRACT FROM AUTHOR]

BBTMPO was synthesized by a condensation of 4-n butyl benzaldehyde and 4-amino 2,2,6,6-tetramethyl piperidine N-oxide (4-tempamine). The shape of the resulting spin probe, estimated using the Dreiding models, is a spherocone of length 10.7 Å capped by hemispheres of radii 6.6 and 4.0 Å, respectively. The magnetic parameters of BBTMPO in toluene at 77 K were determined. Variable temperature ESR line shape studies in the temperature range of 142–211 K revealed that BBTMPO exhibited anisotropic rotational diffusion in toluene along the long axis of the spherocone and in the direction parallel to the N–O bond. Rotational diffusion along the long axis was found to be 3±0.5 and 7±0.5 times faster for frozen and liquid toluene, respectively, than the other two axes. The line shapes have been simulated by using the stochastic Liouville theory of slow-motional effects on ESR spectrum. The slow tumbling spectrum (158 K) in the model-sensitive region showed good agreement for a Brownian model. The plot of τR vs 1/T over the whole temperature range yield a good linear fit with two slopes, with the activation energy for reorientation process of 4.9 kcal/mol in the liquid state, and 9.9 kcal/mol in the solid state. The higher activation energy of rotational reorientation coupled with a lower anisotropy of molecular reorientation (N) in the solid state, indicates that the rotational degrees of freedom is more restricted in the frozen state than in the liquid state. Molecular reorientation for BBTMPO in toluene was analyzed in terms of the hydrodynamic free space model for molecular relaxation in liquids. The stickiness factor S was found to be 0.6 while the anisotropic interaction parameter κ which measures the coupling of rotation to translation was found to be 0.7. For perdeuterated 2,2,6,6-tetramethyl-4-piperidine N-oxide (PD-Tempone) in toluene the stickiness factor was calculated to be 0.3, and κ was 0.4. The doubling in... [ABSTRACT FROM AUTHOR]

Presents a study that investigated the variations of Raman spectra for silicon-implanted gallium antimonide (GaSb) with various doses and energies. Advantages of ion-implantation technology over diffusion; Analysis of the Raman spectrum of the unimplanted GaSb wafer; Reasons for the broadening and weakening of the transverse and longitudinal optical phonon modes.

Temperature-dependent photoreflectance (PR) measurements are employed to characterize the conduction band structure of In0.54Ga0.46P1-yNy (y=0 and 0.02) grown on GaAs substrates. The band gap and the upper subband E+ transition are observed in InGaPN as predicted by the band anticrossing (BAC) model. To investigate the energetic positions of the features in the PR spectra, a Kramers–Kronig analysis is proposed. Based on the PR data and the BAC model, we find that the energy EN of isolated nitrogen states shifts significantly to higher energies with decreasing temperature. Simultaneously, the interaction potential V between the nitrogen states and the unperturbed conduction band also rises to higher values. At 293 K, EN=2.054 eV and V=1.513 eV are determined. The thermal shifts of EN and V are dEN/dT≈-0.43 meV/K and dV/dT≈-0.67 meV/K, respectively. The temperature-dependent EN level and interaction potential V are attributed to the lattice distortions, which can be affected by temperature-induced changes in deformation potential. This information is important for overall validity of the BAC model to dilute nitride InGaPN alloys. [ABSTRACT FROM AUTHOR]

Coordination polymers exhibiting magnetic properties can be considered as promising materials for magnetic applications. We obtained such materials by means pf mechanochemical incorporation of binuclear metal complexes Mn–O–Mn into polystyrene. Incorporation of binuclear manganese complexes was achieved by using substituted benzoquinones (organic acceptors) as intermediate ligands that react with manganese acetylacetonate and provide new coordination and stabilization of manganese in different valence states. Magnetic transitions in this system are due to reversible disproportionation process Mn3+–O–Mn3+⇔Mn2+–O–Mn4+ in the binuclear complex. The structure of the binuclear complex was obtained using ab initio calculations. [ABSTRACT FROM AUTHOR]

We report on mechanochemical synthesis and magnetic and electric properties of organic polymeric semiconductor that contains paramagnetic and ferromagnetic particles. As starting materials we used polyaniline (emeraldine base), polystyrene, FeCl3, and elemental sulfur. These components were chosen for the purpose of obtaining semiconductor polymer composite containing magnetic iron nanoparticles and having flexible thermomechanical properties. The presence of nanoparticles was evidenced by scanning electron microscopy. The value of conductivity of the Fe-doped polymer composite was increased by several orders of magnitude compared to the initial undoped polyaniline. Temperature dependence of the conductivity shows semiconductor character of the composite material. [ABSTRACT FROM AUTHOR]

Abstract: The brackish cyclopoid copepod Apocyclops royi is used in Taiwanese aquaculture industry as a prey for fish larvae. This study investigated the effects of seven microalgal diets, namely single‐species diets of Isochrysis galbana (ISO), Nannochloropsis oculata (NAN), and Tetraselmis chui (TET), two‐species diets (ISO+NAN, ISO+TET and TET+NAN), and a three‐species diet (ISO+NAN+TET), on the population growth, female fecundity and fatty acid composition of A. royi. For reproductive traits, the combination ISO+NAN was found to be the most supportive diet for both population growth and female fecundity. For nutritional value, copepods fed ISO and ISO+NAN were detected to have the highest content of docosahexaenoic acid (DHA) (18.99% and 10.73% total fatty acid, respectively) and, more importantly, a high DHA/EPA ratio (6.09 and 4.09, respectively). Additionally, a comparison of fatty acid composition between copepods and microalgae gives a tentative indication that A. royi may have the ability to synthesize long‐chain polyunsaturated fatty acids (PUFA) from short‐chain PUFA. Our findings illustrate that ISO+NAN is the most suitable microalgal diet for mass culturing A. royi because it increases productivity and enhances the nutritional value of the copepods for use as fish larvae prey. [ABSTRACT FROM AUTHOR]

By means of mechanochemical synthesis we obtained a coordination polymer containing binuclear manganese complexes with organic catechol/ortho-quinone ligands. The reaction system contained polystyrene, manganese acetylacetonate, and donor-acceptor mixture catechol/ortho-quinone. Electron paramagnetic resonance (EPR) and infrared spectroscopic data show that the binuclear manganese complex is covalently linked to the chain of polystyrene. Theoretical EPR spectrum analysis revealed a triplet state of the complex with two nonequivalent manganese ions coupled to each other by spin exchange. The type of magnetic coupling between manganese ions in this system is similar to the one in manganese based inorganic magnetic materials. [ABSTRACT FROM AUTHOR]